U.S. patent number RE39,065 [Application Number 08/794,374] was granted by the patent office on 2006-04-18 for switching voltage regulator circuit.
This patent grant is currently assigned to Linear Technology Corporation. Invention is credited to Carl T. Nelson.
United States Patent |
RE39,065 |
Nelson |
April 18, 2006 |
Switching voltage regulator circuit
Abstract
An integrated circuit for use in implementing a switching
voltage regulator, the integrated circuit including a power
switching transistor, driver circuitry and control circuitry, which
is operable in a normal feedback mode or an isolated flyback mode.
The integrated circuit includes shutdown circuitry for placing the
regulator in a micro-power sleep mode, and can be packaged in a
five-pin conventional power transistor package. The terminals of
the integrated circuit regulator perform multiple functions. A
compensation terminal is used for frequency compensation, current
limiting, soft-start operation and shutdown. A feedback terminal is
used as a feedback input when the integrated circuit is in feedback
mode, and as a logic pin to program the regulator for isolated
flyback operation. The feedback terminal is also used to trim the
flyback reference voltage.
Inventors: |
Nelson; Carl T. (San Jose,
CA) |
Assignee: |
Linear Technology Corporation
(Milpitas, CA)
|
Family
ID: |
26768067 |
Appl.
No.: |
08/794,374 |
Filed: |
December 10, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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08558204 |
Nov 16, 1995 |
|
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|
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07683549 |
Apr 10, 1991 |
|
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06932158 |
Nov 18, 1986 |
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Reissue of: |
07082989 |
Aug 3, 1987 |
04823070 |
Apr 18, 1989 |
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Current U.S.
Class: |
323/284 |
Current CPC
Class: |
H02M
3/33507 (20130101); H02M 1/36 (20130101); H02M
3/33523 (20130101); Y02B 70/10 (20130101); H02M
1/0032 (20210501) |
Current International
Class: |
G05F
1/40 (20060101) |
Field of
Search: |
;323/284,282,287,285,267,299 ;363/20,97,13,21,131 |
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|
Primary Examiner: Riley; Shawn
Attorney, Agent or Firm: Fish & Neave IP Group Ropes
& Gray LLP Rowland; Mark D. Chang; Chi-Hsin
Parent Case Text
.Iadd.This is a continuation of application Ser. No. 08/558,204,
filed Nov. 16, 1995, which is a continuation of application Ser.
No. 07/683,549, filed Apr. 10, 1991, entitled Switching Voltage
Regulator Circuit. .Iaddend.
This is a continuation of application Ser. No. 932,158, filed Nov.
18, 1986, entitled "SWITCHING VOLTAGE REGULATOR CIRCUIT", now
abandoned.
Claims
What is claimed is:
1. An integrated circuit for use in a switching voltage regulator
circuit, the switching voltage regulator circuit providing a
regulated voltage output at an output terminal, the integrated
circuit including internal drive circuitry, a power switching
transistor and control circuitry for varying the switching duty
cycle of the switching transistor, the integrated circuit having at
most five terminals including an input terminal, an output terminal
a ground terminal and first and second function terminals for
connection to discrete external components to implement the
switching voltage regulator circuit, the integrated circuit
comprising: first means connected to one of the function terminals
for accepting a feedback signal from the output of the switching
voltage regulator circuit and for enabling the integrated circuit
to operate in a first mode to regulate the output of the switching
voltage regulator by varying the duty cycle of the switching
transistor as a function of the magnitude of the feedback signal;
second means connected to the input and output terminals for
enabling the integrated circuit to operate in an isolated flyback
mode to regulate the output of the switching voltage regulator
circuit as a function of a feedback voltage developed across a
primary winding of a discrete external transformer; and mode select
means connected to one of the function terminals and to said first
and second means to disable the first means and to enable the
second means in response to a disable signal applied to that
function terminal by the discrete components.
2. An integrated circuit for use in a switching voltage regulator
circuit providing a regulated output voltage, the integrated
circuit having internal drive circuitry, a power switching
transistor and control circuitry for varying the on and off
switching duty cycle of the switching transistor, and further
having an input terminal, an output terminal, a ground terminal and
first and second function terminals for connection to external
components, the integrated circuit comprising: first means
connected to the first function terminal and to the control
circuitry for accepting a first feedback signal indicative of the
regulated output voltage, and for enabling the integrated circuit
to operate in a normal feedback mode to regulate the regulated
output voltage by varying the duty cycle of the switching
transistor as a function of the magnitude of the first feedback
signal; second means connected to the input and output terminals
and to the control circuitry for accepting a second feedback signal
between the input and output terminals indicative of a voltage
developed across a winding of an external transformer, and for
enabling the integrated circuit to operate in a fully isolated
flyback mode to regulate the regulated output voltage as a function
of the magnitude of the second feedback signal; and third means
connected to one of the function terminals and to said first and
second means to disable one of the first and second means and to
enable the other in response to a control signal applied to that
function terminal by external components.
3. The integrated circuit of claim 2, wherein said first means
includes: means for producing a first reference signal; and means
for detecting a difference between the first feedback signal and
the first reference signal, and for generating an error signal
indicative of that difference; and wherein the control circuitry
includes: means for comparing the error signal to a signal
indicative of the magnitude of current conducted by the switching
transistor; and means responsive to said comparing means for
turning off the switching transistor when the current magnitude
signal exceeds the error signal.
4. The integrated circuit of claim 2, wherein said second means
includes: means responsive to the second feedback signal for
generating an error signal indicative of a difference between the
second feedback signal and a predetermined threshold signal level;
and wherein the control circuitry includes: means for comparing the
error signal to a signal indicative of the magnitude of current
conducted by the switching transistor, and means responsive to said
comparing means for turning off the switching transistor when the
current magnitude signal exceeds the error signal.
5. The integrated circuit of claim 2, wherein said first means
includes: means for producing a first reference signal; and means
for detecting a difference between the first feedback signal and
the first reference signal, and for generating a first error signal
indicative of that difference; wherein said second means includes:
means responsive to the second feedback signal for generating a
second error signal indicative of a difference between the second
feedback signal and a predetermined threshold signal level; and
wherein the control circuitry includes: means for receiving the
first and second error signals, for comparing at any given time one
of the first and second error signals to a signal indicative of the
magnitude of current conducted by the switching transistor; and
means responsive to said comparing means for turning off the
switching transistor when the current magnitude signal exceeds the
compared one of the first and second error signals.
6. The integrated circuit of claim 3, wherein said means for
generating an error signal includes a differential amplifier having
a first input for receiving the feedback signal and a second input
for receiving the first reference signal.
7. The integrated circuit of claim 4, wherein said means for
generating the second feedback error signal includes: an amplifier
having a first input connected to one of the input and output
terminals; and means connected to a second input of said amplifier
and to the other of the input and output terminals for establishing
a threshold voltage, whereby a voltage differential is established
across the inputs of the amplifier when a voltage difference
between the input and output terminals exceeds the threshold
voltage.
8. The integrated circuit of claim 7, wherein said means for
establishing a threshold voltage includes a zener diode.
9. The integrated circuit of claim 8, wherein said zener diode has
a zener breakdown voltage, and wherein said means for establishing
a threshold voltage further includes: means for establishing a
trimming voltage in series with the zener breakdown voltage such
that at least a part of the threshold voltage is comprised of the
sum of the trimming and zener breakdown voltages; and means
connected to said means for establishing a trimming voltage, and to
one of the function terminals, for varying the trimming voltage in
response to a signal at that function terminal, thereby varying the
threshold voltage.
10. The integrated circuit of claim 9, wherein said means for
varying the trimming voltage is connected to the first function
terminal.
11. The integrated circuit of claim 10, wherein: said means for
establishing a trimming voltage comprises a resistor; and wherein
said means for varying the trimming voltage varies a current
conducted by said trimming voltage resistor as a function of a
current conducted by the first function terminal.
12. The integrated circuit of claim 11, wherein the current
conducted by the first function terminal is established at least in
part by external components connected to the first function
terminal.
13. The integrated circuit of claim 12, wherein the external
components connected to the first function terminal includes a
resistor connected to ground.
14. The integrated circuit of claim 2, wherein said third means is
connected to the first function terminal.
15. The integrated circuit of claim 14, wherein the control signal
is a current, and wherein said third means includes: means for
sensing the current conducted by the first function terminal; and
means responsive to said sensing means for disabling said first
means and enabling said second means when the current sensed by
said sensing means exceeds a predetermined threshold current.
16. The integrated circuit of claim 2, wherein said third means is
connected to the first function terminal, and wherein the
integrated circuit further comprises: fourth means connected to the
control circuitry and to the second function terminal for
performing at least two of: (a) frequency compensating the
integrated circuit, (b) limiting the peak current conducted by the
switching transistor, (c) variably limiting the current conducted
by the switching transistor as a function of time, and (d) shutting
down the integrated circuit, whereby the current drawn by the
integrated circuit is reduced.
17. The integrated circuit of claim 16, wherein said fourth means
includes: means for generating a signal indicative of the magnitude
of current conducted by the switching transistor; means connected
to at least one terminal of the integrated circuit for sensing a
feedback signal from the discrete components indicative of the
magnitude of at least one of the regulated output voltage and the
voltage developed across the winding of the external transformer,
and for generating an error signal indicative of the difference
between the feedback signal and a reference signal; means for
comparing the error signal to the current magnitude signal, and for
turning off the switching transistor when the current magnitude
signal exceeds the error signal; and means for applying the error
signal to the second function terminal, whereby the magnitude of
the error signal may be controlled by a network of one or more
external components connected to the second function terminal.
18. The integrated circuit of claim 17, wherein the network of
external components connected to the second function terminal
includes a frequency compensating capacitor.
19. The integrated circuit of claim 17, wherein the network of
external components connected to the second function terminal
includes a frequency compensation capacitor in series with a
resistor.
20. The integrated circuit of claim 17, wherein the network of
external components connected to the second function terminal
prevents the error signal at the second function terminal from
exceeding a predetermined maximum level, thereby limiting to a
maximum peak value the magnitude of current conducted by the
switching transistor.
21. The integrated circuit of claim 20, wherein the network of
external components establishes a predetermined maximum voltage at
the second function terminal.
22. The integrated circuit of claim 17, wherein the network of
external components connected to the second function terminal
variably controls the voltage at the second function terminal as a
function of time, thereby variably limiting as a function of time
the current conducted by the switching transistor.
23. The integrated circuit of claim 22, wherein the network of
external components for variably controlling the voltage at the
second function terminal includes: a resistor connected between a
first node and a second node; a capacitor connected between the
second node and the ground terminal; and means connected between
the second node and the second function terminal for applying at
least a portion of a voltage at the second node to the second
function terminal, such that the voltage at the second function
terminal upon application of a voltage at the first node gradually
increases with time to gradually increase the current conducted by
the switching transistor.
24. The integrated circuit of claim 17, the integrated circuit
further having voltage regulator circuitry for providing a
regulated voltage to at least portions of the internal drive
circuitry, and wherein said fourth means further includes: means
for producing second reference signal; means for comparing the
second reference signal to a shutdown control signal applied to the
second function terminal by the external components, and for
generating a shutdown signal when the second reference signal and
the shutdown control signal differ by a predetermined amount; and
means responsive to the shutdown signal for disabling at least the
voltage regulator circuitry, thereby shutting down and reducing the
current drawn by the integrated circuit.
25. The integrated circuit of claim 24, wherein the shutdown
control signal is a voltage, and wherein: said means for producing
a second reference signal includes a diode having a first forward
voltage drop; and wherein said means for comparing the second
reference signal to the shutdown control signal includes a
transistor having a base-emitter circuit connected between said
diode and the second function terminal, the base-emitter circuit
having a second forward voltage drop which differs from the first
forward voltage drop, and said transistor being adapted to disable
the voltage regulator circuitry when the shutdown control signal
voltage at the second function terminal is less than the difference
between the first and second forward voltage drops.
26. An integrated circuit for use in implementing a switching
voltage regulator providing a regulated output voltage, the
integrated circuit having a power switching transistor, circuitry
for driving the switching transistor and control circuitry for
varying the on and off switching duty cycle of the switching
transistor, and further having for connection to external
components an input terminal, an output terminal, a ground terminal
and a function terminal, the integrated circuit comprising: first
means connected to the function terminal and to the control
circuitry for accepting a first feedback signal indicative of the
regulated output voltage, and for enabling the integrated circuit
to operate in a normal feedback mode to regulate the regulated
output voltage by varying the duty cycle of the switching
transistor as a function of the magnitude of the first feedback
signal; second means connected to at least one of the terminals and
to the control circuitry for accepting a second feedback signal
indicative of a voltage developed across a winding of an external
transformer, and for enabling the integrated circuit to operate in
a fully isolated flyback mode to regulate the output voltage as a
function of the magnitude of the second feedback signal; and mode
select means connected to the function terminal and to said first
and second means to disable one of the first and second means and
to enable the other in response to a mode select control signal
applied to the function terminal by external components.
27. The integrated circuit of claim 26, wherein said first means
includes: means for producing a first reference signal; and means
for detecting a difference between the first feedback signal and
the first reference signal, and for generating an error signal
indicative of that difference; and wherein the control circuitry
includes: means for comparing the error signal to a signal
indicative of the magnitude of current conducted by the switching
transistor; and means responsive to said comparing means for
turning off the switching transistor when the current magnitude
signal exceeds the error signal.
28. The integrated circuit of claim 26, wherein said second means
includes: means responsive to the second feedback signal for
generating an error signal indicative of a difference between the
second feedback signal and a predetermined threshold signal level;
and wherein the control circuitry includes: means for comparing the
error signal to a signal indicative of the magnitude of current
conducted by the switching transistor; and means responsive to said
comparing means for turning off the switching transistor when the
current magnitude signal exceeds the error signal.
29. The integrated circuit of claim 26, wherein said first means
includes: means for producing a first reference signal; and means
for detecting a difference between the first feedback signal and
the first reference signal, and for generating a first error signal
indicative of that difference; wherein said second means includes:
means responsive to the second feedback signal for generating a
second error signal indicative of a difference between the second
feedback signal and a predetermined threshold signal level; and
wherein the control circuitry includes: means for receiving the
first and second error signals, and for comparing at any given time
one of the first and second error signals to a signal indicative of
the magnitude of current conducted by the switching transistor; and
means responsive to said comparing means for turning off the
switching transistor when the current magnitude signal exceeds the
compared one of the first and second error signals.
30. The integrated circuit of claim 27, wherein said means for
generating an error signal includes a differential amplifier having
a first input for receiving the first feedback signal and a second
input for receiving the first reference signal.
31. The circuit of claim 28, wherein said means for generating the
second feedback error signal includes: an amplifier having a first
input connected to one of the input and output terminals; and means
connected to a second input of said amplifier and to the other of
the input and output terminals for establishing a threshold
voltage, whereby a voltage differential is established across the
inputs of the amplifier when a voltage difference between the input
and output terminals exceeds the threshold voltage.
32. The circuit of claim 31, wherein said means for establishing a
threshold voltage includes a zener diode.
33. The circuit of claim 32, wherein said zener diode has a zener
breakdown voltage, and wherein said means of establishing a
threshold voltage further includes: means for establishing a
trimming voltage in series with the zener breakdown voltage such
that at least a part of the threshold voltage is comprised of the
sum of the trimming and zener breakdown voltages; and means
connected to said means for establishing a trimming voltage, and to
the function terminal, for varying the trimming voltage in response
to a signal at the function terminal, thereby varying the threshold
voltage.
34. The circuit of claim 33 wherein: said means for establishing a
trimming voltage comprises a resistor; and wherein said means for
varying the trimming voltage varies a current conducted by said
trimming voltage resistor as a function of a current conducted by
the function terminal.
35. The circuit of claim 34, wherein the current conducted by the
function terminal is established at least in part by external
components connected to the function terminal.
36. The circuit of claim 35, wherein the external components
connected to the function terminal include a resistor connected to
ground.
37. The circuit of claim 26, wherein said mode select means is
connected to the function terminal.
38. The circuit of claim 37, wherein said mode select means
includes: means for sensing current conducted by the function
terminal; and means responsive to said sensing means for disabling
said first means and enabling said second means when the current
sensed by said sensing means exceeds a predetermined threshold
current.
39. The circuit of claim 38, wherein the function terminal is
connected to external components adapted to conduct a current which
exceeds the threshold current.
40. An integrated circuit for use in implementing a switching
voltage regulator providing a regulated output voltage, the
integrated circuit having a power switching transistor, circuitry
for driving the switching transistor and control circuitry for
varying the on and off switching duty cycle of the switching
transistor, and further having at most five terminals for
connection to external components consisting of an input terminal,
an output terminal, a ground terminal and first and second function
terminal, the integrated circuit comprising: first means connected
to the first function terminal and to the control circuitry for
accepting a first feedback signal indicative of the regulated
output voltage, and for enabling the integrated circuit to operate
in a normal feedback mode to regulate the regulated output voltage
by varying the duty cycle of the switching transistor as a function
of the magnitude of the first feedback signal; second means
connected to at least one of the input and output terminals and to
the control circuitry for accepting a second feedback signal
indicative of a voltage developed across a winding of an external
transformer, and for enabling the integrated circuit to operate in
a fully isolated flyback mode to regulate the regulated output
voltage as a function of the magnitude of the second feedback
signal; mode select means connected to the first function terminal
and to said first and second means to disable one of the first and
second means and to enable the other in response to a mode select
control signal applied to the first function terminal by external
components; and means connected to the control circuitry and to the
second function terminal for enabling the switching voltage
regulator circuit in response to signals applied to the second
function terminal by a network of external components to be
frequency compensated.
41. The integrated circuit of claim 40, wherein said first means
includes: means for producing a first reference signal; and means
for detecting a difference between the first feedback signal and
the first reference signal, and for generating an error signal
indicative of that difference; and wherein the control circuitry
includes: means for comparing the error signal to a signal
indicative of the magnitude of current conducted by the switching
transistor; and means responsive to said comparing means for
turning off the switching transistor when the current magnitude
signal exceeds the error signal.
42. The integrated circuit of claim 40, wherein said second means
includes: means responsive to the second feedback signal for
generating an error signal indicative of a difference between the
second feedback signal and a predetermined threshold signal level;
and wherein the control circuitry includes: means for comparing the
error signal to a signal indicative of the magnitude of current
conducted by the switching transistor; and means responsive to said
comparing means for turning off the switching transistor when the
current magnitude signal exceeds the error signal.
43. The integrated circuit of claim 40, wherein said first means
includes: means for producing a first reference signal; and means
for detecting a difference between the first feedback signal and
the first reference signal, and for generating a first error signal
indicative of that difference; wherein said second means includes:
means responsive to the second feedback signal for generating a
second error signal indicative of a difference between the second
feedback signal and a predetermined threshold signal level; and
wherein the control circuitry includes: means for receiving the
first and second error signals, for comparing at any given time one
of the first and second error signals to a signal indicative of the
magnitude of current conducted by the switching transistor; and
means responsive to said comparing means for turning off the
switching transistor when the current magnitude signal exceeds the
compared one of the first and second error signals.
44. The integrated circuit of claim 40, wherein said means for
generating an error signal includes a differential amplifier having
a first input for receiving the first feedback signal and a second
input for receiving the first reference signal.
45. The circuit of claim 42, wherein said means for generating the
second feedback error signal includes: an amplifier having a first
input connected to one of the input and output terminals; and means
connected to a second input of said amplifier and to the other of
the input and output terminals for establishing a threshold
voltage, whereby a voltage differential is established across the
inputs of the amplifier when a voltage difference between the input
and output terminals exceeds the threshold voltage.
46. The circuit of claim 45, wherein said means for establishing a
threshold voltage includes a zener diode.
47. The circuit of claim 46, wherein said zener diode has a zener
breakdown voltage, and wherein said means for establishing a
threshold voltage further includes: means for establishing a
trimming voltage in series with the zener breakdown voltage such
that at least a part of the threshold voltage is comprised of the
sum of the trimming and zener breakdown voltages; and means
connected to said means for establishing a trimming voltage, and to
one of the function terminals, for varying the trimming voltage in
response to a signal at that function terminal, thereby varying the
threshold voltage.
48. The circuit of claim 47, wherein said means for varying the
trimming voltage is connected to the first function terminal.
49. The circuit of claim 48, wherein: said means of establishing a
trimming voltage comprises a resistor; and wherein said means for
varying the trimming voltage varies a current conducted by said
trimming voltage resistor as a function of a current conducted by
the first function terminal.
50. The circuit of claim 49, wherein the current conducted by the
first function terminal is established at least in part by external
components connected to the first function terminal.
51. The circuit of claim 50, wherein the external components
connected to the first function terminal include a resistor
connected to ground.
52. The circuit of claim 40, wherein said mode select means is
connected to the first function terminal.
53. The circuit of claim 40, wherein said mode select means
includes: means for sensing current conducted by the first function
terminal; and means responsive to said sensing means for disabling
said first means and enabling said second means when the current
sensed by said sensing means exceeds a predetermined threshold
current.
54. The integrated circuit of claim 39, wherein the network of
external components connected to the second function terminal
includes a frequency compensating capacitor.
55. The integrated circuit of claim 40, wherein the network of
external components connected to the second function terminal
includes a frequency compensation capacitor in series with a
resistor.
56. An integrated circuit for use in implementing a switching
voltage regulator providing a regulated output voltage, the
integrated circuit having internal drive circuitry, a power
switching transistor and control circuitry for controlling the on
and off duty cycle of the switching transistor to produce a pulsed
output, and further having input and ground terminals for
connection to a source of input power, an output terminal for
connection to external components adapted to convert the pulsed
output of the switching transistor into the regulated output
voltage, and first and second multi-function terminals for
connection to external components adapted to apply control signals
to the multi-function terminals, the integrated circuit comprising:
first means responsive to control signals applied to the first
multi-function terminal, said first means including at least two
of: (a) means for controlling the duty cycle of the switching
transistor when the integrated circuit is operating in a normal
feedback mode, (b) means for programming the integrated circuit to
operate in one of a normal feedback mode and a fully-isolated
flyback mode, and (c) means for trimming a flyback voltage
developed across a winding of an external transformer when the
integrated circuit operates in a fully-isolated flyback mode; and
second means responsive to control signals applied to the second
multi-function terminal for performing at least two of: (a)
frequency compensating the integrated circuit, (b) limiting peak
current conducted by the switching transistor, (c) variably
limiting current conducted by the switching transistor as a
function of time, and (d) shutting down the integrated circuit,
whereby current drawn by the integrated circuit is reduced.
57. The integrated circuit of claim 56, wherein said normal
feedback mode controlling means includes: means for producing a
first reference signal; means for generating a feedback mode error
signal indicative of a difference between the first reference
signal and a feedback signal applied to the first multi-function
terminal indicative of the magnitude of the regulated output
voltage; means for comparing the feedback mode error signal to a
signal indicative of the magnitude of current conducted by the
switching transistor; and means responsive to said comparing means
for turning off the switching transistor when the current magnitude
signal exceeds the error signal, whereby the duty cycle of the
switching transistor is controlled as a function of the feedback
signal.
58. The integrated circuit of claim 56, wherein said programming
means includes: means for controlling the duty cycle of the
switching transistor when the integrated circuit operates in a
fully-isolated flyback mode; and means connected to the first
multi-function terminal for sensing a mode-select signal at the
first multi-function terminal and for responsively disabling said
normal feedback mode controlling means and enabling said flyback
mode controlling means.
59. The integrated circuit of claim 58, wherein said flyback mode
controlling means includes: means connected to the input and output
terminals for receiving a flyback signal indicative of a voltage
developed across the winding of the external transformer, and for
generating a flyback mode error signal indicative of a difference
between the flyback signal and a threshold signal level; means for
comparing the flyback mode error signal to a signal indicative of
the magnitude of current conducted by the switching transistor; and
means responsive to the output of said comparing means for turning
off the switching transistor when the current magnitude signal
exceeds the error signal, whereby the duty cycle of the switching
transistor is controlled as a function of the flyback signal.
60. The integrated circuit of claim 59, wherein said trimming means
includes: means connected to the first multi-function terminal for
sensing a trimming control signal; and means connected to said
trimming control signal sensing means and to said flyback mode
error signal generating means for trimming the magnitude of the
threshold signal in response to the trimming control signal,
thereby trimming the flyback voltage.
61. The integrated circuit of claim 56, wherein said second means
includes: means for generating a signal indicative of the magnitude
of current conducted by the switching transistor; means connected
to at least one terminal of the integrated circuit for sensing a
feedback signal indicative of the magnitude of at least one of the
regulated output voltage and the voltage developed across the
winding of the external transformer, and for generating an error
signal indicative of the difference between the feedback signal and
a reference signal; means for comparing the error signal to the
current magnitude signal, and for turning off the switching
transistor when the current magnitude signal exceeds the error
signal; and means for applying the error signal to the second
multi-function terminal, whereby the magnitude of the error signal
may be controlled by a network of one or more external components
connected to the second multi-function terminal.
62. The integrated circuit of claim 61, wherein the network of
external components connected to the second multi-function terminal
includes a frequency compensating capacitor.
63. The integrated circuit of claim 61, wherein the network of
external components connected to the second multi-function terminal
includes a frequency compensation capacitor in series with a
resistor.
64. The integrated circuit of claim 61, wherein the network of
external components connected to the second multi-function terminal
prevents the error signal at the second multi-function terminal
from exceeding a predetermined maximum level, thereby limiting to a
maximum peak value the magnitude of current conducted by the
switching transistor.
65. The integrated circuit of claim 62, wherein the network of
external components establishes a predetermined maximum voltage at
the second multi-function terminal.
66. The integrated circuit of claim 61, wherein the network of
external components connected to the second multi-function terminal
variably controls the voltage at the second multi-function terminal
as a function of time, thereby variably limiting as a function of
time the current conducted by the switching transistor.
67. The integrated circuit of claim 66, wherein the network of
external components for variably controlling the voltage at the
second multi-function terminal includes: a resistor connected
between a first node and a second node; a capacitor connected
between the second node and the ground terminal; and means
connected between the second node and the second multi-function
terminal for applying at least a portion of a voltage at the second
node to the second multi-function terminal, such that the voltage
at the second multi-function terminal upon application of a voltage
at the first node gradually increases with time to gradually
increase the current conducted by the switching transistor.
68. The integrated circuit of claim 56, the integrated circuit
further having voltage regulator circuitry for providing a
regulated voltage to at least portions of the internal Circuitry,
wherein said second means further includes: means for producing a
second reference signal; means for comparing the second reference
signal to a shutdown control signal applied to the second
multi-function terminal by the external components, and for
generating a shutdown signal when the second reference signal and
the shutdown control signal differ by a predetermined amount; and
means responsive to the shutdown signal for disabling at least the
voltage regulator circuitry, thereby shutting down and reducing the
current drawn by the integrated circuit.
69. The integrated circuit of claim 68, wherein the shutdown
control signal is a voltage, and wherein: said means for producing
a second reference signal includes a diode having a first forward
voltage drop; and wherein said comparing means includes a
transistor having a base-emitter circuit connected between said
diode and the second multi-function terminal, the base-emitter
circuit having a second forward voltage drop which differs from the
first forward voltage drop, and said transistor being adapted to
disable the voltage regulator circuitry when the shutdown control
signal voltage at the second multi-function terminal is less than
the difference between the first and second forward voltage
drops.
70. An integrated circuit for use in implementing a switching
voltage regulator providing a regulated output voltage, the
integrated circuit having internal drive circuitry, a power
switching transistor and control circuitry for controlling the on
and off duty cycle of the switching transistor to produce a pulsed
output, and further having input and ground terminals for
connection to a source of input voltage and current, an output
terminal for connection to external components adapted to convert
the pulsed output of the switching transistor into the regulated
output voltage, and first and second multi-function terminals for
connection to external components adapted to apply control signals
to the multi-function terminals, the integrated circuit comprising:
first means responsive to control signals applied to the first
multi-function terminal, said first means including: (a) means for
controlling the duty cycle of the switching transistor when the
integrated circuit operates in a normal feedback mode, (b) means
for programming the integrated circuit to operate in one of a
normal feedback mode and a fully-isolated flyback mode, and (c)
means for trimming a flyback voltage developed across a winding of
an external transformer when the integrated circuit operates in a
fully-isolated flyback mode; and second means responsive to control
signals applied to the second multi-function terminal for: (a)
frequency compensating the integrated circuit, (b) limiting peak
current conducted by the switching transistor, (c) variably
limiting current conducted by the switching transistor as a
function of time, and (d) shutting down the integrated circuit,
whereby current drawn by the integrated circuit is reduced.
71. An integrated circuit for use in implementing a switching
voltage regulator providing a regulated output voltage, the
integrated circuit having internal drive circuitry, a power
switching transistor and control circuitry for controlling the on
and off duty cycle of the switching transistor to produce a pulsed
output, and further having input and ground terminals for
connection to a source of input voltage and current, an output
terminal for connection to external components adapted to convert
the pulsed output of the switching transistor into the regulated
output voltage, and first and second multi-function terminals for
connection to external components adapted to apply control signals
to the multi-function terminals, the integrated circuit comprising:
first means responsive to control signals applied to the first
multi-function terminal, said first means including: (a) means for
controlling the duty cycle of the switching transistor when the
integrated circuit operates in a normal feedback mode, (b) means
for programming the integrated circuit to operate in one of a
normal feedback mode and a fully-isolated flyback mode, and (c)
means for trimming a flyback voltage developed across a winding of
an external transformer when the integrated circuit operates in a
fully-isolated flyback mode; and second means responsive to control
signals applied to the second multi-function terminal for: (a)
frequency compensating the integrated circuit, (b) limiting peak
current conducted by the switching transistor, and (c) variably
limiting current conducted by the switching transistor as a
function of time.
72. An integrated circuit for use in implementing a switching
voltage regulator providing a regulated output voltage, the
integrated circuit having internal drive circuitry, a power
switching transistor and control circuitry for controlling the on
and off duty cycle of the switching transistor to produce a pulsed
output, and further having input and ground terminals for
connection to a source of input voltage and current, an output
terminal for connection to external components adapted to convert
the pulsed output of the switching transistor into the regulated
output voltage, and first and second multi-function terminals for
connection to external components adapted to apply control signals
to the multi-function terminals, the integrated circuit comprising:
first means responsive to control signals applied to the first
multi-function terminal, said first means including: (a) means for
controlling the duty cycle of the switching transistor when the
integrated circuit operates in a normal feedback mode, and (b)
means for programming the integrated circuit to operate in one of a
normal feedback mode and a fully-isolated flyback mode; and second
means responsive to control signals applied to the second
multi-function terminal for: (a) frequency compensating the
integrated circuit, (b) limiting peak current conducted by the
switching transistor, (c) variably limiting current conducted by
the switching transistor as a function of time, and (d) shutting
down the integrated circuit, whereby current drawn by the
integrated circuit is reduced.
73. An integrated circuit for use in implementing a switching
voltage regulator providing a regulated output voltage, the
integrated circuit having internal drive circuitry, a power
switching transistor and control circuitry for controlling the on
and off duty cycle of the switching transistor to produce a pulsed
output, and further having input and ground terminals for
connection to a source of input voltage and current, an output
terminal for connection to external components adapted to convert
the pulsed output of the switching transistor into the regulated
output voltage, and first and second function terminals for
connection to external components adapted to apply control signals
to the function terminals, the integrated circuit comprising: first
means responsive to a control signal applied to the first function
terminal for controlling the duty cycle of the switching transistor
as a function of the magnitude of the regulated output voltage; and
second means responsive to control signals applied to the second
function terminal for: (a) frequency compensating the integrated
circuit, (b) limiting .Iadd.peak .Iaddend.current conducted by the
switching transistor, (c) variably limiting current conducted by
the switching transistor as a function of time, and (d) shutting
down the integrated circuit, whereby current drawn by the
integrated circuit is reduced.
74. An integrated circuit for use in implementing a switching
voltage regulator providing a regulated output voltage, the
integrated circuit having internal drive circuitry power switching
transistor and control circuitry for controlling the on and off
duty cycle of the switching transistor to produce a pulsed output,
and further having input and ground terminals for connection to a
source of input voltage and current, an output terminal for
connection to external components adapted to convert the pulsed
output of the switching transistor into the regulated output
voltage, and first and second multi-function terminals for
connection to external components adapted to apply control signals
to the multi-function terminals, the integrated circuit comprising:
first means responsive to control signals applied to the first
multi-function terminal, said first means including: (a) means for
controlling the duty cycle of the switching transistor when the
integrated circuit operates in a normal feedback mode, and (b)
means for programming the integrated circuit to operate in one of a
normal feedback mode and a fully-isolated flyback mode; second
means responsive to control signals applied to the second
multi-function terminal for: (a) frequency compensating the
integrated circuit, (b) limiting peak current conducted by the
switching transistor, and (c) variably limiting current conducted
by the switching transistor as a function of time.
75. An integrated circuit for use in implementing a switching
voltage regulator providing a regulated output voltage, the
integrated circuit having internal drive circuitry, a power
switching transistor and control circuitry for controlling the on
and off duty cycle of the switching transistor to produce a pulsed
output, the integrated circuit comprising: at most five terminals
for connection to external components, including input and ground
terminals for connection to a source of input power, and output
terminal for connection to external components adapted to convert
the pulsed output of the switching transistor into the regulated
output voltage, and first and second multi-function terminals for
connection to external components adapted to apply control signals
to the multi-function terminals; first means responsive to control
signals applied to the first multi-function terminal, said first
means including at least two of: (a) means for controlling the duty
cycle of the switching transistor when the integrated circuit is
operating in a normal feedback mode, (b) means for programming the
integrated circuit to operate in one of a normal feedback mode and
a fully-isolated flyback mode, and (c) means for trimming a flyback
voltage developed across a winding of an external transformer when
the integrated circuit operates in a fully-isolated flyback mode;
and second means responsive to control signals applied to the
second multi-function terminal for performing at least two of: (a)
frequency compensating the integrated circuit, (b) limiting peak
current conducted by the switching transistor, (c) variably
limiting current conducted by the switching transistor as a
function of time, and (d) shutting down the integrated circuit,
whereby current drawn by the integrated circuit is reduced.
76. An integrated circuit for use in implementing a switching
voltage regulator providing a regulated output voltage, the
integrated circuit having internal drive circuitry, a power
switching transistor and control circuitry for controlling the on
and off duty cycle of the switching transistor to produce a pulsed
output, the integrated circuit comprising: at most five terminals
for connection to external components, including input and ground
terminals for connection to a source of input power, an output
terminal for connection to external components adapted to convert
the pulsed output of the switching transistor into the regulated
output voltage, and first and second multi-function terminals for
connection to external components adapted to apply control signals
to the multi-function terminals; first means responsive to control
signals applied to the first multi-function terminal, said first
means including: (a) means for controlling the duty cycle of the
switching transistor when the integrated circuit is operating in a
normal feedback mode, (b) means for programming the integrated
circuit to operate in one of a normal feedback mode and a
fully-isolated flyback mode, and (c) means for trimming a flyback
voltage developed across a winding of an external transformer when
the integrated circuit operates in a fully-isolated flyback mode,
and second means responsive to control signals applied to the
second multi-function terminal for: (a) frequency compensating the
integrated circuit, (b) limiting peak current conducted by the
switching transistor, (c) variably limiting current conducted by
the switching transistor as a function of time, and (d) shutting
down the integrated circuit, whereby current drawn by the
integrated circuit is reduced.
77. An integrated circuit for use in implementing a switching
voltage regulator providing a regulated output voltage, the
integrated circuit having internal drive circuitry, a power
switching transistor and control circuitry for controlling the on
and off duty cycle of the switching transistor to produce a pulsed
output, the integrated circuit comprising: at most five terminals
for connection to external components, including input and ground
terminals for connection to a source of input power, an output
terminal for connection to external components adapted to convert
the pulsed output of the switching transistor into the regulated
output voltage, and first and second multi-function terminals for
connection to external components adapted to apply control signals
to the multi-function terminals; first means responsive to control
signals applied to the first multi-function terminal, said first
means including: (a) means for controlling the duty cycle of the
switching transistor when the integrated circuit is operating in a
normal feedback mode, (b) means for programming the integrated
circuit to operate in one of a normal feedback mode and a
fully-isolated flyback mode, and (c) means for trimming a flyback
voltage developed across a winding of an external transformer when
the integrated circuit operates in a fully-isolated flyback mode;
and second means responsive to control signals applied to the
second multi-function terminal for performing at least two of: (a)
frequency compensating the integrated circuit, (b) limiting peak
current conducted by the switching transistor, and (c) variably
limiting current conducted by the switching transistor as a
function of time.
78. An integrated circuit for use in implementing a switching
voltage regulator providing a regulated output voltage, the
integrated circuit having internal drive circuitry, a power
switching transistor and control circuitry for controlling the on
and off duty cycle of the switching transistor to produce a pulsed
output, the integrated circuit comprising: at most five terminals
for connection to external components, including input and ground
terminals for connection to a source of input power, an output
terminal for connection to external components adapted to convert
the pulsed output of the switching transistor into the regulated
output voltage, and first and second multi-function terminals for
connection to external components adapted to apply control signals
to the multi-function terminals; first means responsive to control
signals applied to the first multi-function terminal, said first
means including at least two of: (a) means for controlling the duty
cycle of the switching transistor when the integrated circuit is
operating in a normal feedback mode, and (b) means for programming
the integrated circuit to operate in one of a normal feedback mode
and a fully-isolated flyback mode; and second means responsive to
control signals applied to the second multi-function terminal for
performing at least two of: (a) frequency compensating the
integrated circuit, (b) limiting peak current conducted by the
switching transistor, (c) variably limiting current conducted by
the switching transistor as a function of time, and (d) shutting
down the integrated circuit, whereby current drawn by the
integrated circuit is reduced.
79. An integrated circuit for use in implementing a switching
voltage regulator providing a regulated output voltage, the
integrated circuit having internal drive circuitry, a power
switching transistor and control circuitry for controlling the on
and off duty cycle of the switching transistor to produce a pulsed
output, the integrated circuit comprising: at most five terminals
for connection to external components, including input and ground
terminals for connection to a source of input power, an output
terminal for connection to external components adapted to convert
the pulsed output of the switching transistor into the regulated
output voltage, and first and second function terminals for
connection to external components adapted to apply control signals
to the function terminals; first means responsive to control
signals applied to the first function terminal for controlling the
duty cycle of the switching transistor as a function of the
magnitude of the regulated output voltage; and second means
responsive to control signals applied to the second function
terminal for: (a) frequency compensating the integrated circuit,
(b) limiting peak current conducted by the switching transistor,
(c) variably limiting current conducted by the switching transistor
as a function of time, and (d) shutting down the integrated
circuit, where.Iadd.by .Iaddend.current drawn by the integrated
circuit is reduced.
80. An integrated circuit for use in implementing a switching
voltage regulator providing a regulated output voltage, the
integrated circuit having internal drive circuitry, a power
switching transistor and control circuitry for controlling the on
and off duty cycle of the switching transistor to produce a pulsed
output, the integrated circuit comprising: at most five terminals
for connection to external components, including input and ground
terminals for connection to a source of input power, an output
terminal for connection to external components adapted to convert
the pulsed output of the switching transistor into the regulated
output voltage, and first and second multi-function terminals for
connection to external components adapted to apply control signals
to the multi-function terminals; first means responsive to control
signals applied to the first multi-function terminal, said first
means including: (a) means for controlling the duty cycle of the
switching transistor when the integrated circuit is operating in a
normal feedback mode, and (b) means for programming the integrated
circuit to operate in one of a normal feedback mode and a
fully-isolated flyback mode; and second means responsive to control
signals applied to the second multi-function terminal for
performing at least two of: (a) frequency compensating the
integrated circuit, (b) limiting peak current conducted by the
switching transistor, and (c) variably limiting current conducted
by the switching transistor as a function of time.
81. An integrated circuit capable of implementing a current-mode
normal feedback switching voltage regulator and a current-mode
fully isolated flyback switching voltage regulator, the integrated
circuit having a switching transistor, circuitry for driving the
switching transistor, and control circuitry for controlling the on
and off duty cycle of the switching transistor to produce a pulsed
output, the integrated circuit comprising: at most five terminals
for connection to external components, including: (a) input and
ground terminals, connected to the integrated circuitry, for
connection to a source of input voltage and current; (b) an output
terminal, connected to the switching transistor, for connection to
external components adapted to convert the pulsed output of the
switching transistor into the regulated output voltage; (c) a first
multi-function terminal responsive to control signals applied by
external components connected to the first multi-function terminal
for performing at least two functions selected from the group of:
(1) controlling the duty cycle of the switching transistor when the
integrated circuit is operating in a normal feedback mode, (2)
programming the integrated circuit to operate in one of a normal
feedback mode and fully-isolated flyback mode, and (3) trimming a
flyback voltage developed across a winding of an external
transformer when the integrated circuit operates in a
fully-isolated flyback mode; and (d) a second multi-function
terminal, responsive to control signals applied by external
components connected to the second multi-function terminal, for
performing at least two functions selected from the group of: (1)
frequency compensating the integrated circuit, (2) limiting peak
current conducted by the switching transistor, (3) variably
limiting current conducted by the switching transistor as a
function of time, and (4) shutting down the integrated circuit,
whereby current drawn by the integrated circuit is reduced.
.Iadd.82. An integrated circuit for implementing a current-mode
switching voltage regulator circuit by connecting the integrated
circuit to external components, the integrated circuit comprising:
at most five terminals, the terminals comprising input and ground
terminals for connecting the integrated circuit to a source of
input voltage and current, an output terminal for connecting the
integrated circuit to an external inductive or transformer load, a
feedback terminal for receiving an external feedback signal
proportional to the regulated output voltage of the switching
regulator, and a compensation terminal for connection to an
external frequency compensation network; a power switching
transistor having its collector-emitter circuit coupled to conduct
a current between the output terminal and the ground terminal;
means coupled to the switching transistor for varying the on and
off duty cycle of the switching transistor in response to a control
signal; means including a resistive element coupled in series with
the collector-emitter circuit of the switching transistor, and an
amplifier coupled to the resistive element for generating a current
sense signal indicative of the current conducted by the switching
transistor; means for generating an error signal indicative of a
difference between the feedback signal and a reference signal;
means for coupling the error signal to the compensation terminal;
and means for comparing the current sense signal to the error
signal and for generating the control signal to turn off the
switching transistor when the current sense signal compares in a
predetermined manner to the error signal to vary the duty cycle of
the switching transistor to produce the regulated output voltage.
.Iaddend.
.Iadd.83. The integrated circuit of claim 82 further comprising:
means responsive to control signals applied to the compensation
terminal for performing at least one of: (a) limiting peak current
conducted by the switching transistor, (b) variably limiting
current conducted by the switching transistor as a function of
time, and (c) shutting down the integrated circuit, whereby current
drawn by the integrated circuit is reduced. .Iaddend.
.Iadd.84. The integrated circuit of claim 82, wherein the control
signal is generated when the current sense signal exceeds the error
signal. .Iaddend.
.Iadd.85. An integrated circuit for implementing a current-mode
switching voltage regulator circuit by connecting the integrated
circuit to external components, the integrated circuit comprising:
at least an input terminal and a ground terminal for connecting the
integrated circuit to a source of input voltage and current, an
output terminal for connecting the integrated circuit to an
external inductive or transformer load, a feedback terminal for
receiving an external feedback signal proportional to the regulated
output voltage of the switching regulator, and a compensation
terminal for connection to an external frequency compensation
network; a power switching transistor structure coupled to conduct
current between the output terminal and the ground terminal; a
driver circuit coupled to provide a base drive current to the
switching transistor; a circuit coupled to the driver circuit for
varying the on and off duty cycle of the switching transistor in
response to a control signal; a circuit including a resistive
element coupled in series with the current path in the switching
transistor between the output terminal and the ground terminal and
an amplifier coupled to the resistive element for generating a
current sense signal indicative of the current conducted by the
switching transistor; a circuit for generating an error signal
indicative of a difference between the feedback signal and a
reference signal, and for coupling the error signal to the
compensation terminal and to the driver circuit; a reference
circuit coupled to provide the reference signal to the circuit for
generating an error signal; a circuit for comparing the current
sense signal to the error signal and for generating the control
signal to turn off the switching transistor when the current sense
signal compares in a predetermined way to the error signal to vary
the duty cycle of the switching transistor to produce the regulated
voltage, the comparing circuit further being responsive to control
signals externally applied to the compensation terminal for
performing at least one of (a) limiting peak current conducted by
the switching transistor, and (b) variably limiting current
conducted by the switching transistor as a function of time; and a
circuit for placing the integrated circuit into a shutdown state
where the current drawn by the integrated circuit is reduced,
including by deactivating the reference circuit; wherein: the
driver circuit is responsive at least in part to the error signal
for causing the base drive current provided to the switching
transistor to vary so as to increase the efficiency of operation of
the switching transistor. .Iaddend.
.Iadd.86. The integrated circuit of claim 85, wherein the circuit
for placing the integrated circuit into a shutdown state is
responsive to a signal externally applied to the compensation
terminal. .Iaddend.
.Iadd.87. The integrated circuit of claim 86, wherein the switching
transistor structure is a bipolar transistor. .Iaddend.
.Iadd.88. An integrated circuit for implementing a current-mode
switching regulator circuit by connecting the integrated circuit to
external components, the integrated circuit comprising: at least an
input terminal and a ground terminal for connecting the integrated
circuit to a source of input voltage and current, an output
terminal for connecting the integrated circuit to an external
inductive or transformer load, a feedback terminal for receiving an
external feedback signal proportional to the regulated output
voltage of the switching regulator, and a compensation terminal for
connection to an external frequency compensation network; a power
switching transistor structure coupled to conduct current between
the output terminal and the ground terminal; a circuit coupled to
the switching transistor structure for varying the on and off duty
cycle of the switching transistor in response to a control signal;
a circuit, including a resistive element coupled in series with a
current path in the switching transistor structure between the
output terminal and the ground terminal and an amplifier coupled to
the resistive element, for generating a curernt sense sigal
indicative of the current conducted by the switching transistor; a
circuit for generating an error signal indicative of a difference
between the feedback signal and a reference signal, and for
coupling the error signal to the compensation terminal; and a
circuit for comparing the current sense signal to the error signal
and for generating the control signal to turn off the switching
transistor when the current sense signal compares in a
predetermined way to the error signal to vary the duty cycle of the
switching transistor to produce the regulated voltage, said
comparing circuit further being responsive to control signals
externally applied to the compensation terminal for (a) limiting
peak current conducted by the switching transistor and (b) variably
limiting current conducted by the switching transistor as a
function of time, wherein the integrated circuit terminals require
connection to no more than five different nodes among the external
components to implement a current-mode switching regulator circuit.
.Iaddend.
.Iadd.89. The integrated circuit of claim 88, further comprising a
circuit for reducing the current drawn by the integrated circuit to
place the integrated circuit into a shutdown state. .Iaddend.
.Iadd.90. The integrated circuit of claim 89, wherein the circuit
for reducing the current drawn by the integrated circuit is
responsive to a signal externally applied to the compensation
terminal. .Iaddend.
.Iadd.91. The integrated circuit of claim 89, wherein the switching
transistor structure is a bipolar transistor. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an integrated circuit switching
voltage regulator circuit having multi-function terminals. More
particularly, the present invention relates to an integrated
circuit for use in implementing a switching voltage regulator
circuit, the integrated circuit requiring only five terminals,
operable in both feedback and isolated flyback mode, and including
a power switching element, a driver network, and control circuitry
which sets the duty cycle of the switching element.
The function of a voltage regulator is to provide a predetermined
and substantially constant output voltage level from an unregulated
input voltage. Two types of voltage regulators are commonly used
today: linear regulators and switching regulators.
A linear regulator controls output voltage by controlling the
voltage drop across a power transistor which is connected in series
with a load. The power transistor is operated in its linear region
and conducts current continuously.
A switching regulator controls output voltage by using a power
transistor as a switch to provide a pulsed flow of current to a
network of inductive and capacitive energy storage elements which
smooth the switched current pulses into a continuous and regulated
output voltage. The power transistor is operated either in a cutoff
or saturated state at a duty cycle required by the voltage
differential between the input and output voltages. Varying the
duty cycle varies the regulated output voltage of the switching
regulator.
The duty cycle of a switching regulator is controlled by monitoring
output voltage or current through the switch. The latter type of
switching regulator is known as a current-mode switching regulator,
and is easier to frequency stabilize and has better response to
transients than does a switching regulator in which the duty cycle
is controlled directly by output voltage.
Switching regulators have at least two advantages over linear
regulators. First, switching regulators typically operate with
greater efficiency than linear regulators, a particularly important
factor in high current regulators. Second, switching regulators are
more versatile than linear regulators. Switching regulators can
provide output voltages which are less than, greater than, or of
opposite polarity to the input voltage, depending on the mode of
operation of the switching regulator, whereas linear regulators can
only provide output voltages which are less than the input
voltage.
Further, switching regulators can be configured to drive current
through the primary winding of a transformer, the secondary winding
of which simultaneously provides current to the load. The
transformer provides current gain, the amount of which is
determined by the turns ratio of the transformer. Multiple outputs
are possible, each output typically requiring two steering diodes,
an inductor and a capacitor. Alternatively, the transformer may be
configured such that current provided to the primary winding of the
transformer by the regulator switch is stored as energy in the
primary winding and is transferred to the secondary winding only
after the switch driving the primary winding is opened. This
configuration, known as flyback operation, allows multiple
regulated output voltages and requires only one steering diode and
one capacitor for each output.
In either of the above transformer configurations, the isolation
provided by the transformer between input and output circuits is
limited by the need to regulate the output voltage by sensing the
output voltage of the regulator circuit and providing a feedback
voltage signal to the control circuitry of the circuit. The output
circuit driven by the secondary winding of the transformer thus
remains electrically connected to the input circuit driving the
primary winding. Voltage regulator configurations which sense
output voltage of the circuit for use as a feedback signal are
referred to herein as normal feedback mode regulators. Another
configuration, known as an isolated flyback mode regulator, allows
a transformer secondary winding to be totally isolated from the
input circuit connected to the primary winding by regulating the
peak voltage developed across the primary winding when the
secondary winding provides current to the output circuit.
Switching regulators, although more flexible than linear regulators
in circuit applications, are typically more complex than linear
regulators. Although several integrated circuits in the past have
been commercially available for implementing the control, driver
and power switch functions of switching regulators, switching
regulators utilizing such integrated circuits have required
substantial engineering expertise and numerous discrete components
to make them operational. Also, integrated circuits heretofore
available typically required 8-14 terminals for connection to
external discrete components, and could not be configured into a
very low current (shutdown) mode. This quantity of terminals
prevented such integrated circuits from being packaged in low-cost
power transistor packages such as the conventional 5-pin TO-3 type
metal can or the TO-220 type molded plastic packages, and thus
limited the power handling capability of the integrated circuit.
Further, heretofore available integrated circuits for use in
implementing switching voltage regulators have not been capable of
use both in normal feedback mode switching regulator circuits and
isolated flyback mode regulator circuits.
In view of the foregoing, it would be desirable to be able to
provide a switching voltage regulator circuit which is simple to
implement and which is capable of versatile and efficient
operation.
It would further be desirable to be able to provide a switching
regulator circuit, having a very low current sleep mode which can
be implemented as an integrated circuit which includes the power
switch, and which can be packaged in a conventional TO-3 or TO-220
power transistor package.
It would also be desirable to be able to provide an integrated
circuit which can be utilized to implement both normal feedback
mode and isolated flyback mode regulator circuit topologies.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an
integrated circuit for use in implementing a switching voltage
regulator circuit, the integrated circuit being simple to implement
and capable of efficient operation in numerous switching regulator
configurations.
It is a further object of the present invention to provide an
integrated circuit capable of implementing a switching voltage
regulator circuit, and capable of operating in both normal feedback
mode and isolated flyback mode voltage regulator
configurations.
It is yet a further object of the present invention to provide an
integrated circuit, for use in implementing a switching regulator,
which includes control circuitry, driver circuitry and the power
switch, which can be packaged in conventional 5-pin TO-3 or TO-220
power packages, and which is capable of operating in a very low
current sleep mode.
These and other objects of the present invention are accomplished
by a novel switching regulator circuit which can be packaged as an
integrated circuit requiring only five external terminals for
connection to discrete external components. The low number of
terminals is achieved by assigning several functions to individual
terminals. One terminal is used for soft starting, frequency
compensation, switch current limiting and shutdown. Another
terminal is used to receive a feedback signal when the integrated
circuit is operated in a normal feedback mode switching voltage
regulator circuit, and alternatively to place the integrated
circuit into an isolated flyback mode and to vary the flyback
reference voltage in an isolated flyback voltage regulator
circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects and advantages of the invention will be
apparent upon consideration of the following detailed description,
taken in conjunction with the accompanying drawings, in which like
reference characters refer to like parts throughout, and in
which:
FIG. 1 is a block diagram of a five-terminal current-mode switching
voltage regulator integrated circuit of the present invention;
FIG. 2 is a schematic diagram of the switching voltage regulator
integrated circuit of FIG. 1 connected in a normal feedback mode
boost regulator configuration and including a soft-start circuit, a
frequency compensation circuit, and an external current limiting
circuit;
FIG. 3 is a schematic diagram of the switching voltage regulator
integrated circuit of FIG. 1 connected in an isolated flyback mode
switching regulator configuration;
FIG. 4 is a schematic diagram of a preferred embodiment of shutdown
circuit 122 and reference voltage generator 124, as well as
reference 120 and regulator 102, of the switching voltage regulator
integrated circuit of FIG. 1;
FIG. 5 is a schematic diagram of a preferred embodiment of error
amplifier 118 and its interconnection with mode select circuit 126
of the switching voltage regulator integrated circuit of FIG.
1;
FIG. 6 is a schematic diagram of a preferred embodiment of switches
528, 530 and 532 and mode select circuit 126 of FIGS. 1 and 5;
FIG. 7 is a schematic diagram of a preferred embodiment of
comparator 116 of the switching voltage regulator integrated
circuit of FIG. 1; and
FIG. 8 is a schematic diagram of a preferred embodiment of variable
zener diode 130 of the switching voltage regulator of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a five-terminal integrated circuit 100 of the present
invention capable of implementing a current-mode switching voltage
regulator circuit, and capable of being packaged in a conventional
5-pin power package. Five terminals are shown, labeled as V.sub.IN
(input supply), V.sub.SW (output), FB (feedback), V.sub.C
(compensation) and GND (ground).
Terminal V.sub.IN provides a connecting point for input voltage,
and is used to supply power to the internal circuitry of integrated
circuit 100. Terminal V.sub.SW is the output terminal of circuit
100. It provides a connecting point between power switch 110 of
regulator 100 and external components configured to implement a
number of switching regulator topologies, to convert the pulsed
current flowing through switch 110 into a regulated output voltage.
Further, when regulator 100 is operated in an isolated flyback
mode, as discussed further herein, terminal V.sub.SW provides a
flyback reference voltage point which is held to a peak voltage
level which exceeds the voltage at terminal V.sub.IN by a
predetermined amount.
Terminal FB provides three functions. First it serves as an input
for feedback voltage when integrated circuit 100 is operated in a
feedback mode. Second, terminal FB acts as a logic pin for
programming integrated circuit 100 for normal feedback or isolated
flyback operation. As further discussed below, integrated circuit
100 is converted from normal feedback operation to isolated flyback
operation when a current exceeding a predetermined threshold level
is conducted out of terminal FB by connecting terminal FB to ground
through a resistor. Third, terminal FB is used to establish the
relative value (to voltage at V.sub.IN) of the flyback reference
voltage at terminal V.sub.SW. The different functions of terminal
FB, and their implementation, are discussed in greater detail
below.
Terminal V.sub.C provides access to a point in the internal
circuitry of integrated circuit 100 to provide several functions.
First, a frequency compensation circuit may be connected to
terminal V.sub.C to control the closed loop response of integrated
circuit 100. Second, a current limit circuit may be connected to
terminal V.sub.C to limit the peak current through switch 110.
Third, a soft-start circuit may be connected to terminal V.sub.C to
ensure that the width of the initial current pulse flowing through
switch 110 starts from zero and builds up to a proper level
gradually when regulator 100 is first powered up, thereby avoiding
sudden current surges upon start-up of the circuitry. Fourth, a
shutdown circuit may be connected to terminal V.sub.C for placing
regulator 100 into an inactive sleep mode in which the current
drawn by regulator 110 is reduced to a very low value. These
different functions, and their implementation, are described in
greater detail below.
Referring now to the circuitry internal to switching regulator
circuit 100, connected to terminal V.sub.IN is a linear voltage
regulator 102 which regulates the supply voltage applied to
terminal V.sub.IN to provide a substantially constant voltage for
use by the internal circuitry of regulator 100. Voltage regulator
102 may be substantially any conventional voltage regulator circuit
which provides a regulated output voltage of about 2.3V (this
voltage is not critical, and may be varied as desired). Voltage
regulator 102 is discussed in more detail below.
Conventional oscillator 104 is connected to the set input of
conventional set/reset flip-flop 106 to provide flip-flop 106 with
a digital clocking signal. The output of flip-flop 106 is connected
to driver circuitry 108, which in turn is connected to switch 110.
Substantially any conventional driver circuitry may be used to
provide sufficient base drive current to switch transistor 110.
Alternatively, a driver circuit may be used of the type disclosed
in co-pending patent application Ser. No. 932,014 .Iadd. (now U.S.
Pat. No. 4,755,741) .Iaddend.filed Nov. 18, 1986, entitled
"Adaptive Transistor Drive Circuit", filed in the name of Carl T.
Nelson, the disclosure of which is incorporated herein by
reference.
The digital clocking signal provided by oscillator 104, which
preferably has a frequency of approximately 40 kHz, is used to turn
on switch 110 via flip-flop 106 and driver circuitry 108. Switch
110 is a power transistor having a base connected to driver
circuitry 108, a collector connected to terminal V.sub.SW and an
emitter connected to one end of sense resistor 112, the other end
of which is connected to terminal GND.
Flip-flop 106 supplies a signal to driver circuitry 108 in response
to the clock signal provided by oscillator 104. The signal provided
by flip-flop 106 in response to the clock signal causes driver
circuitry 108 to turn on switch 110. When regulator 100 is
configured in a switching regulator with external components as
described below, the current flows between terminal V.sub.SW and
terminal GND as a consequence of the turning on of switch 110 and
through sense resistor 112, which causes a voltage to be generated
across sense resistor 112. Sense resistor 112 in FIG. 1 has a value
of approximately 0.02 ohms, although other values may be used. The
inputs of a conventional common base differential amplifier 114,
preferably having a differential voltage gain of approximately 6,
are connected across sense resistor 112. The output of amplifier
114 is connected to one input (I) of comparator circuit 116 (the
details of which are further discussed with reference to FIG. 7).
Amplifier 114 detects the voltage generated across sense resistor
112 when power transistor 110 conducts, and responsively provides
an amplified signal to input I of comparator 116. The second input
(V) of comparator 116 is connected to the output of an error
amplifier 118 (the details of which also are discussed below with
reference to FIG. 5). The inverting input of error amplifier 118 is
connected to terminal FB. The noninverting input of error amplifier
118 is connected to an internal reference voltage generator 120.
Reference voltage generator 120 is a temperature compensated
band-gap reference voltage circuit (e.g., a Brokaw Cell) having a
voltage output of approximately 1.24V. Error amplifier 118 has a
differential voltage gain of approximately 800-1000, and provides a
maximum output voltage of approximately 2.0V.
Error amplifier 118 detects the difference in voltage between the
voltage at terminal FB and the reference voltage provided by
reference generator 120, and responsively provides an error signal
to the V input of comparator 116. The output of error amplifier 118
is also connected to terminal V.sub.C and to one input of shutdown
circuit 122, a second input of which is connected to reference
voltage generator 124. Reference voltage generator 124, the details
of which are further discussed herein, preferably provides a
reference voltage of approximately 0.15V. The output of shutdown
circuit 122 is connected to regulator 102 and reference voltage
generator 120. As will be explained in greater detail below with
reference to FIG. 4, shutdown circuit 122 provides a shutdown
signal to regulator 102 and reference generator 120 when the
voltage at terminal V.sub.C is externally pulled down below the
0.15V reference voltage provided by reference generator 124.
The on/off duty cycle of switch 110 is determined by the output of
comparator 116, which is connected to the reset input of flip-flop
106. The output state of comparator 116 at any time depends on the
instantaneous values of the voltages at its two inputs. When
integrated circuit 100 is operated in its normal feedback mode, as
described below, a voltage proportional to the regulated output
voltage is applied to terminal FB. Typically the voltage applied to
terminal FB is set by a voltage divider resistor network comprising
two resistors connected in series between the regulated output of
the voltage regulator circuit and ground. Terminal FB is connected
between the two resistors, and the ratio of the resistance values
of the two resistors determines the proportional relationship of
the feedback voltage applied to terminal FB to the regulated output
voltage. The ratio is chosen such that the voltage applied to
terminal FB equals the output voltage of reference generator 120
when the regulated output voltage is at a desired value. Error
amplifier 118 produces a voltage output which changes in proportion
to any difference in voltage between the voltage at terminal FB and
the reference voltage provided by reference generator 120. If the
voltage at terminal FB exceeds the reference voltage, the output
voltage of error amplifier 118 drops proportionally, and if the
voltage at terminal FB falls below the reference voltage, the
output voltage of error amplifier 118 increases proportionally.
This voltage output is applied to input V of comparator 116. The
voltage output of amplifier 114, which is proportional in magnitude
to the current through switch 110, is applied to input I of
comparator 116. As long as the voltage at input V remains higher
than the voltage at input I, comparator 116 remains in an output
state which causes flip-flop 106 to remain set and to thereby
maintain the on condition of switch 110 which was initiated by
oscillator 104. On the other hand, if the voltage at input V
becomes lower than the voltage at input I, comparator 116 changes
its output state to cause flip-flop 106 to reset, thereby causing
driver circuitry 108 to turn off switch 110.
During normal feedback operation, therefore, switch 110 is turned
off when switch current reaches a predetermined level set by the
output of error amplifier 118. If the regulated output voltage
rises above a predetermined steady-state value set by the voltage
divider network and reference voltage generator 120, the duty cycle
of switch 110 is shortened, because the voltage at input V drops as
a result of the voltage differential at the inputs of error
amplifier 118. The voltage at input I reflecting the switch current
crosses the lowered threshold value set by the voltage at input V
earlier in the switch cycle than during steady-state operation. The
shortened duty cycle causes the regulated output voltage to drop
until it reaches its previous steadystate value. If the regulated
voltage falls below the predetermined steady-state value, the duty
cycle of switch 110 is lengthened because error amplifier 118
causes the voltage at input V to increase above its steady-state
value such that the voltage at input I crosses the threshold value
set by the voltage at input V later in the switch cycle than during
steady-state operation. The lengthened duty cycle causes the
regulated output voltage to increase until it reaches its previous
steady-state value.
The voltage V.sub.c at input V of comparator 116 varies between 0.9
and 2.0 volts during normal feedback operation. For a voltage at
input V below 0.9V, the duty cycle of switch 110 is zero. Above
0.9V, and up to 2.0V, switch 110 closes (turns on) at the beginning
of each cycle of oscillator 104 and opens (turns off) when the
switch current (collector current through transistor 110) reaches a
trip level set by the voltage at input V of comparator 116. The
switch current trip level increases from zero, when input V is at a
voltage approximately equal to 0.9V, to approximately 9.0A when the
voltage at input V reaches its maximum value of 2.0V. Because this
voltage appears at terminal V.sub.c, the peak current through
switch 110 can be limited by externally clamping the voltage of
terminal V.sub.c to a set value below the internal clamp value of
2.0V. External current limiting is but one of several functions of
terminal V.sub.C. Other possible functions include frequency
compensation, soft starting, and total regulator shutdown into a
micro-power sleep mode. The implementation of these functions will
be further discussed below.
Terminal FB also serves multiple purposes. During normal feedback
operation of integrated circuit 100, terminal FB acts as the input
point for feedback voltage from the voltage regulator output, as
previously discussed. Terminal FB further acts as a logic pin for
programming regulator 100 for feedback or fully-isolated flyback
operation. Terminal FB is connected to the input of mode select
circuitry 126. Mode select circuitry 126 has an output connected to
error amplifier 118 and to flyback error amplifier 128. Flyback
error amplifier 128 has two inputs, one connected to terminal
V.sub.IN, and the other connected to the anode of a variable zener
diode 130. The cathode of variable zener diode 130 is connected to
terminal V.sub.SW. The output of flyback error amplifier 128 is
connected to the V input of comparator 116.
By connecting terminal FB to ground through an external resistor,
current having a value determined by the resistance value of the
external resistor is drawn out of terminal FB. As a result of the
flow of this current, mode select circuitry 126 disables error
amplifier 118 to effectively remove it from the circuit, and
enables flyback error amplifier 128 to effectively connect its
output to the V input of comparator 116, thereby placing regulator
100 into its isolated flyback mode of operation. A preferred
embodiment of mode select circuitry 126 is discussed below.
In an isolated flyback regulator circuit, discussed in more detail
below with reference to FIG. 3, terminal V.sub.SW is connected to
one end of the primary winding of a transformer, the other end of
which is connected to terminal V.sub.IN. When switch 110 is closed,
current is drawn through the inductive primary winding of the
transformer and energy is stored. This energy is transferred to the
secondary winding when switch 110 opens. Upon the opening of switch
110, a voltage is developed across the primary winding of the
transformer which is proportionally related to the output voltage
of the circuit by the turns ratio of the transformer (ignoring the
offset in output voltage introduced by the forward-voltage drop of
steering diodes connected between the secondary winding and the
output of the circuit).
Flyback error amplifier 128 regulates the voltage differential
developed when switch 110 is opened between terminals V.sub.IN and
V.sub.SW, and consequently that developed across the primary
winding of the transformer, to a value equal to the breakdown
voltage of variable zener diode 130.
On each switch cycle, if the voltage at terminal V.sub.SW rises to
a value which exceeds the voltage at terminal V.sub.IN by more than
the breakdown voltage of variable zener diode 130, a voltage
differential is established at the inputs of flyback error
amplifier 128 which causes the voltage output of flyback error
amplifier 128 to decrease. This in turn lowers the switch current
trip level voltage at input V of comparator 116. Consequently, the
duty cycle of switch 110 is shortened in response to an increase in
the voltage at terminal V.sub.SW above the reference voltage set by
the voltage at terminal V.sub.IN and the breakdown voltage of
variable zener diode 130. Conversely, if the voltage at terminal
V.sub.SW does not reach a value equal to the sum of the voltage at
terminal V.sub.IN and the breakdown voltage of variable zener diode
130, the voltage at the output of flyback error amplifier 128
increases, which in turn raises the switch current trip level
voltage at input V of comparator 116. The duty cycle of switch 110
is thereby increased until the voltage at terminal V.sub.SW during
the open condition of switch 110 exceeds the voltage at V.sub.IN by
the breakdown voltage of variable zener diode 130. During the
period when switch 110 is closed, the voltage at the output of
flyback error amplifier 128 is held substantially constant by a
resistance/capacitance network externally connected to terminal
V.sub.C, as described more fully below. In this manner, integrated
circuit 100, when connected in an isolated flyback regulator
circuit, maintains the peak voltage across the primary winding of a
transformer connected between terminals V.sub.IN and V.sub.SW at
the breakdown voltage of variable zener diode 138, and thereby
regulates the output voltage of the isolated flyback regulator
circuit.
Variable zener diode 130 has a minimum breakdown voltage of
approximately 16V. The actual value of the breakdown voltage is
dependent on the value of the external resistor connecting terminal
FB to the ground, as will be further discussed below. Terminal FB
thus provides a third function in that it permits the regulated
flyback voltage to be trimmed by varying the value of the resistor
connected thereto.
FIGS. 2 and 3 show illustrative application circuits in which
integrated circuit 100 is operated in its normal feedback mode
(FIG. 2) and in its isolated flyback mode (FIG. 3).
Referring first to FIG. 2, a typical implementation of a boost
regulator using integrated circuit 100 in its normal feedback mode
and connected to discrete external components is shown. The boost
regulator provides a regulated output voltage V.sub.OUT which is
higher than the voltage applied at terminal V.sub.IN.
Terminal V.sub.IN of integrated circuit 100 is connected to one end
of inductor 202, the other end of which is connected to terminal
V.sub.SW and to the anode of diode 204. The cathode of diode 204 is
connected to one end of capacitor 206 and to one end of resistor
208. The other end of resistor 208 is connected to one end of
resistor 210 and to terminal FB. The other end of resistor 210 is
connected to ground, to the other end of capacitor 206, and to
terminal GND.
The values of resistors 208 and 210 determine the regulated output
voltage V.sub.OUT. Error amplifier 118 operates in conjunction with
comparator 116, as previously described with respect to FIG. 1, to
cause the on/off duty cycle of switch 100 to adjust to that
necessary to establish the voltage at terminal FB to equal the
reference voltage out of reference generator 120. Resistors 208 and
210 comprise a voltage divider circuit which sets output voltage
V.sub.OUT equal to 1.24 (R1+R2)/R2, where R1 is the value of
resistor 208 and R2 is the value of resistor 210. Resistor 210 is
preferably given the value 1.24 k ohms to set the current through
resistor 210 at 1 mA, but this value can vary from 300 ohms to 10 k
ohms with negligible effect on regulator performance. The value of
resistor 208 is then selected to set V.sub.OUT to a desired value.
To produce an output voltage V.sub.OUT equal to 12V, for example,
resistor 208 has a value of 10.7 k ohms. For an input voltage of 5V
and a switching frequency of 40 k Hz, the value of inductor 202 is
150 .mu.H. Capacitor 206 has a capacitance of approximately 1000
.mu.F. to ensure an effective series resistance of less than 0.04
ohms, which in turn produces a low output voltage ripple. The
foregoing values for the external components shown in FIG. 2 are
provided for purposes of illustration, and not of limitation. Other
values may be used if desired.
FIG. 2 further shows simplified circuits for implementing current
limiting, soft starting, frequency compensation, and shutdown of
integrated circuit 100 to a micro-power sleep mode. As discussed
above, terminal V.sub.C may be used to provide external current
limiting. The peak current through switch 110 can be externally
limited to any value less than 9A by clamping terminal V.sub.C to a
voltage less than 2V. A circuit 211 for externally limiting the
peak current through switch 110, by clamping the voltage at
terminal V.sub.C to a value less than 2.0 volts, is shown in FIG.
2. Current limit circuit 211 is connected to terminal V.sub.C of
regulator 100 via diode 216. Voltage V.sub.x is provided by a
separate regulated voltage or the unregulated input voltage.
Resistor 212 is connected between voltage V.sub.x and one end of
variable resistor 214, and is selected to drop approximately 2V
across variable resistor 214. The value of variable resistor 214 is
preferably kept to 500 ohms or less to maintain a sharp knee in the
current limit curve, although a greater value of resistance may be
used if desired. The current limit can be fixed by replacing
variable resistor 214 with a fixed resistor. Diode 216, connected
between variable resistor 214 and terminal V.sub.C, prevents
current from flowing into terminal V.sub.C. Other external clamp
circuits may be used to provide more precise current limiting.
Terminal V.sub.C also may be used to provide a soft start
operation. This ensures that the switch current is near zero when
supply voltage is first applied to terminal V.sub.IN, and that the
output current rises gradually with time until it reaches its final
value. An implementation of a soft start circuit is shown in FIG.
2. Soft start circuit 217 includes diode 218, resistor 220 and
capacitor 222. The anode of diode 218 is connected to terminal
V.sub.C and its cathode is connected to one end of resistor 220 and
to one end of capacitor 222. The other end of resistor 220 is
connected to terminal V.sub.IN, and the other end of capacitor 222
is connected to terminal GND. Soft start circuit 217 provides a
time-dependent external current limit which prevents regulator 100
from drawing large input currents or from overshooting the desired
output voltage. During startup the voltage at terminal V.sub.C is
clamped by capacitor 222 to less than 0.9 volts and rises gradually
when voltage is first applied to terminal V.sub.IN at a rate
determined by the value of resistor 220 and capacitor 222, thereby
gradually increasing the peak current allowed through switch 110.
Resistor 220 also resets the soft start circuit by providing a
current path to discharge capacitor 222 when the circuit is turned
off. Other soft-start circuits may of course be used.
Terminal V.sub.C further provides a point for introducing frequency
compensation into the negative feedback loop of the switching
voltage regulator circuit. Like any control system incorporating
negative feedback, switching voltage regulators need a frequency
compensation network to ensure that loop gain drops below unity
before excess loop phase shift exceeds 180.degree.. Such
compensation is important in feedback switching voltage regulators,
because the inductive elements in such circuits insert a 90.degree.
phase shift and output capacitors add an additional 90.degree.
phase shift in the feedback loop. In integrated circuit 100, the
use of the output of error amplifier 118 at terminal V.sub.C to
sense current and to set a switch current trip level significantly
reduces inductance-induced phase shift, thus permitting a simple
pole-zero compensation scheme to ensure both loop stability and
good transient response.
Frequency compensation is preferably performed with an RC network
connected between terminals V.sub.C and GND, as shown by frequency
compensation circuit 223 in FIG. 2. One end of capacitor 224 is
connected to terminal V.sub.C, and the other end of capacitor 224
is connected to one end of resistor 226. The other end of resistor
226 is connected to terminal GND. The values of capacitor 224 and
resistor 226 are determined by applying a square-wave generator to
the regulator output and monitoring the voltage at the output.
Initially, the circuit should be overcompensated with a large
capacitor 224, preferably having a capacitance of at least 2 .mu.F,
and a small resistor 226, preferably having a value of
approximately 1 k ohm, to produce a waveform which is single-pole
overdamped. The value of capacitor 224 is then reduced until the
response becomes slightly underdamped, and the value of resistor
226 is increased to introduce a zero into the loop and to thereby
improve damping. Preferably, the smallest value for capacitor 224
and the largest value for resistor 226 which result in no loop
oscillations and rapid loop settling are chosen.
Terminal V.sub.C additionally functions to provide a means for
reducing the current drawn by integrated circuit 100 when it is
desired to deactivate the regulator. As previously discussed with
reference to FIG. 1, this function is implemented in integrated
circuit 100 by shutdown circuit 122 and reference voltage generator
124. When the voltage at terminal V.sub.C is externally clamped to
a value less than the 0.15V reference voltage provided by generator
124, shutdown circuit 122 provides a signal to regulator 102 and to
generator 120 which deactivates both so that the only current drawn
by regulator 100 is a current of 50 .mu.A-100 .mu.A necessary to
bias shutdown circuit 122. The voltage at terminal V.sub.C can be
externally pulled below 0.15V to activate shutdown circuit 122, the
details of which are discussed below, by connecting terminal
V.sub.C to a conventional relay or saturated transistor (not shown
in FIG. 2).
FIG. 3 shows a fully-isolated flyback regulator configuration
employing integrated circuit 100 in its isolated flyback mode to
provide output voltages of .+-.15V from an input voltage of 5V.
Terminal V.sub.IN is connected to a 5V voltage source 302, and to
one end of the primary winding of transformer 304, the other end of
which is connected to terminal V.sub.SW. Transformer 304 has a
turns ratio N equal to 0.875, where N is the ratio of secondary
winding turns to primary winding turns for each output of
transformer 304. Terminal GND is connected to the negative side of
voltage source 302, to one end of frequency compensation capacitor
312, and to one end of variable resistor 314. The other end of
frequency compensation capacitor 312 is connected to terminal
V.sub.c, and the other end of variable resistor 314 is connected to
one end of resistor 316, the other end of which is connected to
terminal FB. Frequency compensation capacitor 312 has a value of
0.01 .mu.F. Variable resistor 314 and resistor 316 have values of 5
K ohms and 400 ohms, respectively.
Integrated circuit 100 is converted from normal feedback mode to
isolated flyback mode when the current drawn from terminal FB by
resistors 314 and 316 exceeds approximately 10 .mu.A at 25.degree.
C. Terminal FB has a voltage of approximately 0.4V when this
current is drawn out of the terminal, although the actual voltage
depends on the value of resistors 314 and 316 because terminal FB
has an output impedance of approximately 200 ohms. For example, a
current of 400 .mu.A in resistors 314 and 316 will reduce the
voltage at terminal FB from 0.4V to 0.3V.
Resistors 314 and 316 also serve to adjust the regulated output
voltage V.sub.OUT. Regulator 100 regulates the voltage (V.sub.PRI)
across the primary of transformer 304 during the off time of switch
110 to V.sub.PRI=16V+7000(V.sub.FB/R), where V.sub.SB is the
voltage at terminal FB and R is the sum of the values of resistors
314 and 316. The regulated output voltage V.sub.OUT is determined
by V.sub.OUT=N[16+7000 (V.sub.FB/R)]-V.sub.f, where V.sub.f is the
forward voltage of diodes 318 and 320 connected to the secondary
winding of transformer 304. Preferably, the term 7000 (V.sub.FB/R)
is set to approximately 2V to permit some adjustment range in
V.sub.OUT.
Connected between the cathode of diode 318 and a center tap of the
secondary winding of transformer 304 is an output capacitor 322,
and connected between the anode of diode 320 and the center tap is
an output capacitor 324. The output capacitors 322 and 324 are
responsible for filtering the output of the flyback regulator
circuit because the flyback converter does not use the inductance
of the transformer as a filter. Preferably, capacitors 322 and 324
have low effective series resistance to minimize output ripple. As
this may require large capacitors, a conventional LC filter (not
shown) also may be used at the output to provide low output
ripple.
FIGS. 2 and 3 illustrate two applications of integrated circuit
100. They are provided only for illustration, and are not
limitations of the present invention. Numerous other switching
voltage regulator topologies may be implemented using integrated
circuit 100. Further details concerning the application of
integrated circuit 100 and such other topologies may be found in
"LT1070 Design Manual, Application Note 19," dated June 1986,
published by Linear Technology Corporation.
FIGS. 4-8 show preferred circuit embodiments for implementing
components of integrated circuit 100 of FIG. 1. Referring first to
FIG. 4, schematic diagrams are shown for shutdown circuit 122,
regulator 102 and reference voltage generators 120 and 124. The
output of error amplifier 118 is connected to terminal V.sub.C and
to the emitter of transistor 402 of shutdown circuit 122. Connected
to the base of transistor 402 is a conventional current source 404
and the base and collector of a transistor diode connected
transistor 406. The emitter of transistor diode 406 is connected to
ground. Transistor 406 is a high V.sub.BE transistor having a
forward voltage which is approximately 0.15 V greater than the
forward base-emitter voltage of transistor 402. The collector of
transistor 402 is connected to the base of transistor 408, to the
non-inverting input of conventional differential error amplifier
410 of regulator 102 and to the emitter of transistor 412. The
collector of transistor 412 is connected to ground and its base is
connected to the output of reference voltage generator 120. Error
amplifier 410, reference generator 120, and resistors 416 and 418
regulate the voltage drop across transistor 414 to provide a
regulated output voltage of approximately 2.3V. Regulator 102 thus
is configured as a conventional linear regulator having a reference
voltage provided by reference voltage generator 120 and employing a
PNP pass transistor to provide low drop-out, although regulator 102
may be any other conventional linear voltage regulator.
The emitter of transistor 408 is connected to conventional current
source 420 and to the base of transistor 422 in reference voltage,
generator 120. The emitter of transistor 422 is connected to one
end of resistor 424, the other end of which is connected to the
reference voltage output 426 of conventional Brokaw-cell band-gap
voltage reference circuit 428, and to the collector of transistor
430. The base of transistor 430 is connected to a point 432 within
band gap circuit 428 which has a positive temperature coefficient
of approximately 2mV/.degree. C., and to one end of resistor 434,
the other end of which is connected to ground.
Band-gap reference circuit 428 provides a voltage of approximately
1.24V at reference output 426 having negative a temperature
coefficient over at least a portion of the range of operating
temperatures of integrated circuit 100 which causes the voltage at
reference output 426 to decrease with increasing temperature. To
increase the temperature stability of the output voltage of
reference voltage generator 120, a voltage having a positive
temperature coefficient is applied to the base of transistor 430.
At a predetermined operating temperature, determined by the values
of resistors 424 and 434, this voltage becomes sufficiently high to
turn on transistor 430 and to thereby cause current to flow through
resistors 424 and 434. The current flowing through resistor 424
causes a voltage drop across resistor 424 which increases the
voltage at the output of reference voltage generator 120 over the
output voltage of band-gap reference circuit 428. The voltage drop
across resistor 424 has a positive temperature coefficient set by
the values of resistors 424 and 434 which is used to offset the
negative temperature coefficient of the output voltage of band-gap
reference circuit 428. Resistors 424 and 434 have values of 200
ohms and 7.9 kilohms, respectively.
Current source 404 provides current to forward bias transistor
diode 406. Because the forward voltage drop across transistor diode
406 is approximately 0.15V greater than the forward base-emitter
voltage drop of transistor 402, transistor 402 remains in an off
condition during normal operation of regulator 100 as the voltage
at terminal V.sub.C varies between 0.9V and 2.0V. However, if the
voltage at terminal V.sub.C is caused to drop below a value equal
to the difference in the forward voltage of transistor diode 406
and the forward base-emitter voltage of transistor 402, which means
that terminal V.sub.C is pulled down to a voltage level below
0.15V, the base-emitter junction of transistor 402 becomes forward
biased and transistor 402 is turned on. The current drawn by
transistor 402 pulls current out of the base of transistor 408,
thereby causing the emitter of transistor 408 to draw current which
turns off transistor 422. This disables reference voltage generator
120. Likewise, when transistor 402 conducts, the non-inverting
input of error amplifier 410 is pulled low, thereby disabling
regulator 102. In the micropower sleep shutdown mode, no current
flows in integrated circuit 100 with the exception of the current
necessary to bias transistors 402, 406 and 408. Typically, this
current has a value in the range of 40 .mu.A-100 .mu.A.
FIG. 5 shows a preferred implementation of mode select circuitry
126 and error amplifier 118 of FIG. 1. Reference voltage generator
124 is connected to the base of transistor 502 of error amplifier
118, and provides to the base a voltage of approximately 1.24V. The
emitter of transistor 502 is connected to a conventional current
source 504, and to the emitter of transistor 506, the base of which
is connected to terminal FB.
The bases of transistors 502 and 506 act as the inputs of error
amplifier 118. Current source 504 causes a current of approximately
50 .mu.A to flow from the junction of the emitters of transistors
502 and 506. The collector of transistor 502 is connected at a node
to one end of switch 528, and to the base and collector 505 of
transistor 508. That node is labelled in FIG. 5 "enable/disable".
The other end of switch 528 is connected to the output of regulator
102, as are the emitters of transistors 508 and 510. The collector
of transistor 506 is connected to the base and collector 509 of
transistor 510, collector 511 of which is connected to the base and
collector of transistor 512 and to one end of resistor 514. The
other end of resistor 514 is connected to the base and collector of
transistor 516 and to the base of transistor 518. Collector 507 of
transistor 508 and the collector of transistor 518 are connected to
the emitter of transistor 512, the collector of transistor 520, one
end of switch 530, and terminal V.sub.C. The areas of collectors
507 and 511 are respectively four times greater than the areas of
collectors 505 and 509.
Transistors 502 and 506 form a differential input stage. The
collector currents are inverted and multiplied by a factor of four
by transistors 508 and 510, the current gains of which are set by
the collector area ratio. The collector current of transistor 508
is further inverted by transistors 516 and 518 to generate a
current fed balanced output at node 534 which can swing from a
maximum voltage of approximately 2.3V set by regulator 102, when
the voltage at terminal FB is pulled low, to a clamp level of
approximately 0.4V set by resistor 514 and transistor 512, when the
voltage at terminal FB rises above the voltage applied to the base
of transistor 502 by generator 124. Resistor 514 has a value of
approximately 3 k ohms although other values may be used to set
different clamp levels.
The other end of switch 530 is connected to conventional current
source 522, which provides a current of approximately 30 .mu.A. The
emitter of transistor 520 is connected to one end of resistor 524,
the other end of which is connected to one end of switch 532. The
other end of switch 532 is connected to the emitters of transistor
diode 526 and transistors 516 and 518, and to current source 504.
The collector and base of transistor diode 526 are connected to the
output of flyback error amplifier 128.
During the normal feedback mode of operation of integrated circuit
100, switches 528, 530 and 532 are open and a feedback voltage is
applied to terminal FB. Error amplifier 118 is enabled while switch
528 is open, and an output voltage therefrom is applied to the V
input of comparator 116. At the same time, the output voltage of
flyback error amplifier 128 is applied to the base of transistor
520. However, because switches 530 and 532 are open, the output of
flyback error amplifier 128 is isolated from terminal V.sub.C
during feedback operation of integrated circuit 100 and effectively
disabled.
In the isolated flyback mode of integrated circuit 100, terminal FB
is pulled low by an external resistor connected to ground and
switch 528 is closed, thus turning off transistor 507 and disabling
error amplifier 118. Switches 530 and 532 are closed only after a
delay of 1.5 microseconds, as discussed below, following the
closing of switch 110. This prevents the flyback error amplifier
128 from attempting to regulate the voltage at terminal V.sub.SW
during any overvoltage spikes caused by the leakage inductance of
the transformer in the flyback regulator circuit. When switches 530
and 532 are closed, the output of flyback amplifier 128 drives
transistor 520, which in turn controls the voltage at terminal
V.sub.C. The current through switch 530 is fixed at 30 .mu.A by
current source 522. The current through switch 532 can rise to a
maximum of approximately 70 .mu.A, allowing terminal V.sub.C to
source current up to 30 .mu.A, or to sink current up to 40 .mu.A,
in the flyback mode. The gm of flyback error amplifier 128 is
typically 300 micromhos. Current source 504 sets the gm of error
amplifier 118 at 4400 micromhos.
Switches 528, 530 and 532, and mode select circuitry 126, are shown
in FIG. 6 in greater detail. The emitter of transistor 602 is
connected to one end of resistor 603, the other end of which is
connected to the inverting input of error amplifier 118. The other
end of resistor 607 is connected to terminal FB. Resistor 603 has a
value of 5 kohms, resistor 605 a value of 1.3 kohms, and resistor
607 a value of 30 ohms. The non-inverting input of error amplifier
118 is connected to the output of reference voltage generator 120
and is provided thereby with a reference voltage of approximately
1.24V. The base of transistor 602 is connected to one end of
resistor 605, the other end of which is connected between resistors
604 and 606. The other end of resistor 604 is connected to the
output of regulator 102 (hereinafter referred to as the 2.3V line).
The other end of resistor 606 is connected through diode 608 to
terminal GND. The collector of transistor 602 is connected to the
base of transistor 610 and to one end of resistor 612, the other
end of which is connected to the 2.3V line and to the emitter of
transistor 610. Collector 609 of transistor 610 is connected to the
collector of transistor 502, shown in FIG. 5, and collector 611 of
transistor 610 is connected to the base of transistor 614.
The emitter of transistor 614 is connected to terminal GND, and its
collector is connected to one end of resistor 616, the other end of
which is connected to one emitter of transistor 520, and to the
emitter of transistor 618. Resistor 616 has a value of
approximately 24 kilohms. The base of transistor 618 is connected
to current source 638, to the collector of transistor 620 and to
one end of capacitor 622, the other end of which is connected to
the emitter of transistor 620. Current source 638 provides a
current of approximately 20 .mu.A. The base of transistor 620 is
connected to driver circuitry 108 and is turned on and off by
driver circuitry 108 in phase with the turning on and off of power
switch transistor 110. The collector of transistor 618 is connected
to current source 636, to the base and collector of transistor
diode 624, the emitter of which is connected to terminal GND
through resistor 626, and to the base of transistor 628. Current
source 636 provides a current of approximately 100 .mu.A. The
emitter of transistor 628 is connected to an emitter of transistor
520, and to terminal GND through resistor 630, which has a value of
1.0 kilohms. The collector of transistor 628 is connected to the
emitter of transistor 632, and to the 2.3V line through resistor
634, which has a value of approximately 1.3 kilohms. The collector
of transistor 632 is connected to the collector of transistor 520,
to the V input of comparator 115 and to terminal V.sub.C. The base
of transistor 632 is connected to the base and collector of
transistor diode 636, the emitter of which is connected to the 2.3V
line. Transistors 632 and 636, and resistor 634, correspond to
current source 522 of FIG. 5, and provide a 30 .mu.A current to the
collector of transistor 520.
The base of transistor 520 is connected to the output of flyback
error amplifier 128 and to the base and collector of transistor
diode 526, the emitter of which is connected to terminal GND as
shown in FIG. 5.
Resistors 604 and 606, which have values of approximately 5.8
kilohms and 500 ohms, respectively, and diode 608 bias the base of
transistor 602 at a voltage of approximately 1V. When an external
resistor is connected between terminal FB and ground, such that
current is drawn out of terminal FB, the voltage at terminal FB is
clamped to approximately 0.4V by transistor 602. The current drawn
through transistor 602 causes transistor 610 to turn on, thereby
providing current to the collector of transistor 502 (shown in FIG.
5) and the base of transistor 614. In this manner, transistor 610
acts as switch 528 in FIG. 5, disabling error amplifier 118 as
before described when an external resistor is connected between
terminal FB and ground.
Driver circuitry 108 provides a drive current to the base of
transistor 620 when switch 110 is closed which forward biases
transistor 620 into saturation. The current drawn by transistor 620
holds transistor 618 in an off condition, which in turn allows
transistor 628 to conduct. The on condition of transistor 628 pulls
the emitter of transistor 632 low, turning off transistor 632.
Transistor 628 acts as switch 530, disabling current source 522
while switch 110 is closed. The on condition of transistor 628 also
holds the emitter of transistor 520 at a sufficiently high voltage
to maintain transistor 520 in an off condition, thereby isolating
the output of flyback amplifier 128 from input V of comparator 116.
In this manner, transistor 628 also acts as switch 532, preventing
flyback error amplifier 128 from regulating the voltage at terminal
V.sub.SW while switch 110 is closed.
Upon the opening of switch 110, driver circuitry 108 causes
transistor 620 to turn off. Capacitor 622, which has a capacitance
of 40 pF, is charged by the current from current source 638. After
approximately 1.5 microseconds, the voltage across capacitor 622
causes transistor 618 to conduct, which in turn forces transistor
628 into an off condition. This permits transistors 520 and 632 to
turn on and enables flyback error amplifier 128 to regulate the
voltage at terminal V.sub.SW. The 1.5 microsecond delay between the
closing of switch 110 and the enabling of flyback amplifier 128
prevents overvoltage spikes from degrading the regulation of the
flyback converter. While regulator 100 is in its flyback mode, and
during the periods when flyback error amplifier 128 is disabled,
the voltage at terminal V.sub.C is held to its previous value by
the frequency compensation network connected to terminal
V.sub.C.
FIG. 7 shows a preferred embodiment for implementing comparator 116
of FIG. 1. Transistor 702 has a first collector 705 connected to
the reset input of flip-flop 106 and to current source 704, and
remote collector 706 which is connected to the base of transistor
702. Current source 704 provides a current of approximately 50
.mu.A. The emitter of transistor 702 is connected to the output of
amplifier 114 and to current source 708, which provides a current
of approximately 330 .mu.A. The base and remote collector 706 of
transistor 702 are connected to the emitter of transistor 710, and
to current source 712, which provides a current of approximately 50
.mu.A. The collector of transistor 710 is connected to the output
of regulator 102, which provides a voltage of approximately 2.3V.
The base of transistor 710 is connected to terminal V.sub.C through
resistor 714.
The voltage at the base of transistor 702 is approximately equal to
the voltage at terminal V.sub.C minus the base-emitter voltage drop
of transistor 710. When the voltage at terminal V.sub.C is higher
than the voltage at the output of amplifier 114, the base-emitter
junction of transistor 702 is reverse-biased, and the reset input
of flip-flop 106 is held low by current source 704, maintaining
flip-flop 106 in the set condition initiated by oscillator 104.
When the voltage at terminal V.sub.C drops below the voltage at the
output of amplifier 114, indicating that the current passing
through switch 110 has reached the switch current trip level,
transistor 702 turns on and activates the reset input of flip-flop
106, thereby causing switch 110 to open.
As transistor 702 saturates, collector 706 begins to conduct
current. This prevents current source 712 from pulling the base of
transistor 702 to ground, and thereby prevents the deactivation of
the reset input of flip-flop 106 which might otherwise result from
the saturation of transistor 702.
FIG. 8 shows a preferred embodiment of flyback error amplifier 128
and variable zener diode 130. Referring first to variable zener
diode 130, terminal V.sub.SW is connected to the base and collector
of transistor diode 802 of zener diode 130, and to the collector of
power switch transistor 110. The base of power switch transistor
110 is connected to the output of driver circuitry 108, and its
emitter is connected to one end of sense resistor 112, the other
end of which is connected to terminal GND as before described. The
emitter of transistor diode 802 is connected to the cathode of
zener diode 806, the anode of which is connected to the cathode of
zener diode 808. Zener diodes 806 and 808 each have a breakdown
voltage of approximately 7.0V, although zener diodes having other
values of breakdown voltage may be used, as will be appreciated.
The anode of zener diode 808 is connected to the emitter of
transistor diode 810, the collector and base of which are connected
to one end of resistor 812 and to the collector of transistor 814.
Resistor 812 has a value of approximately 7 kilohms.
Resistor 812 is also connected to the collector of transistor 816,
the base of which is connected to the output of regulator 102, and
the emitter of which is connected to one end of resistor 818. The
other end of resistor 818, which preferably has a value of
approximately 200 ohms, is connected to the collector of transistor
820, the base of which is connected to one end of resistor 605 and
to the base of transistor 602 of mode select circuitry 126. The
emitter of transistor 820 is connected to one end of resistor 603
and to one end of resistor 607. The connection of transistor 602,
resistors 603, 604, 605, 606 and 607, and diode 608 is the same as
discussed for the mode select circuit of FIG. 6.
The emitter of transistor 814 is connected to the emitter of
transistor 820 of flyback amplifier 128. Collector 822 of
transistor 820 of flyback amplifier 128 is connected to the base of
transistor 520, shown in FIG. 5. Collector 824, which has an area
approximately four times less than that of collector 822, and the
base of transistor 820 are connected to the base and collector of
transistor diode 826, and to current source 828, which provides a
current of 75 .mu.A to bias transistor 820. The emitter of
transistor diode 826 is connected to terminal V.sub.IN.
As discussed in connection with FIG. 6, integrated circuit 100 is
placed into its flyback mode by pulling a threshold current ranging
from 3 .mu.A to 30 .mu.A out of terminal FB. This current is drawn
through the emitters of transistors 602 and 820, which conduct
substantially equal amounts of current up to a value of
approximately 1 .mu.A, at which point resistor 603 begins to reduce
the percentage of current conducted by transistor 602. Resistor 603
limits the maximum current conducted by transistor 602 to
approximately 30 .mu.A, forcing any additional current drawn out of
terminal FB to be conducted by transistor 820. The current
conducted by transistor 820 flows through resistor 812, creating a
proportional voltage drop from the collector to the base of
transistor 814. This voltage drop increases the effective breakdown
voltage of variable zener diode 130, which is comprised by
transistor diodes 802 and 810, zener diodes 806 and 808, and
transistor 814. The effective breakdown voltage is determined by
summing the voltage drops across the base-emitter junctions of
transistor 814 and transistor diodes 802 and 810, the breakdown
voltages of zener diodes 806 and 808, and the voltage across
resistor 812, and is approximately equal to 16V+7000 (V.sub.FB/R),
where 7000 is the value of resistor 812, V.sub.SB is the voltage at
terminal FB, R is the value of the external resistor tying terminal
FB to ground, and the term 7000 (V.sub.FB/R) represents the voltage
across resistor 812. The voltage at terminal FB is approximately
0.4V when a current of 30 .mu.A is pulled out of terminal FB. Due
to the output impedance of terminal FB, which is approximately 200
ohms, this voltage drops to approximately 0.3V when a current of
500 .mu.A is pulled out of terminal FB. Neglecting the variation in
voltage V.sub.SB due to output impedance, it can be seen that the
effective breakdown voltage of variable zener diode 130 is
dependent on the value of the resistor connected to terminal FB.
For example, a 1.0 kohm resistor tied between terminal FB and
ground results in an effective breakdown voltage of approximately
18.5V. Thus, the flyback reference voltage set by the effective
breakdown voltage of variable zener diode 130 can be trimmed by
varying the value R of the external resistor tying terminal FB to
ground.
Current source 828, transistor diode 826 and transistor 820
comprise flyback error amplifier 128. When the voltage at terminal
V.sub.SW exceeds the voltage at terminal V.sub.IN by more than the
effective breakdown voltage of variable zener diode 130, zener
diodes 806 and 808 conduct, causing transistor 820 to turn on.
Transistor 820 provides current to the base of transistor 520
causing it to turn on and to pull down the voltage at the V input
of comparator 116, thereby lowering the switch current trip level
and shortening the duty cycle of switch 110. When the voltage at
terminal V.sub.SW does not exceed the voltage at V.sub.IN by at
least the effective breakdown voltage of variable zener diode 130,
transistor 820 does not conduct, and transistor 520 is turned off.
At the same time, current source 522, shown in FIG. 5, provides a
current of approximately 30 .mu.A to the V input of comparator 116
which causes the voltage at the V input to increase, thereby
raising the switch current trip level and consequently lengthening
the duty cycle of switch 110.
While preferred embodiments of the invention have been set forth
for purposes of the disclosure, modification of the disclosed
embodiments may occur to those of skill in the art. For example,
while the multi-function terminal feature of the present invention
has been disclosed in the context of an integrated circuit for use
in implementing a current-mode switching voltage regulator, it will
of course be understood by those of skill in the art that the
invention may be employed to implement a 5-terminal integrated
circuit for use with voltage-mode switching voltage regulator
topologies having a micro-power sleep mode capability.
Thus, a switching voltage regulator circuit including control
circuitry, driver circuitry and a power switching device, capable
of being implemented as an integrated circuit requiring only five
terminals having multiple functions, including micro-power mode
shutdown circuitry, and operable in a normal feedback mode as well
as in an isolated flyback mode, has been disclosed. The invention
can readily be packaged in a 5-pin power transistor integrated
circuit package. One skilled in the art will appreciate that the
present invention can be practiced by other than the described
embodiments, which are presented for purposes of illustration and
not of limitation, and the present invention is limited only by the
claims which follow.
* * * * *