U.S. patent application number 14/732413 was filed with the patent office on 2016-12-08 for bjt driver with dynamic adjustment of storage time versus input line voltage variations.
The applicant listed for this patent is Power Integrations Limited. Invention is credited to Manoj Bhasin, Adrian Kirilov Lefedjiev, Matthew David Waterson, Antonius Jacobus Johannes Werner.
Application Number | 20160359403 14/732413 |
Document ID | / |
Family ID | 57452370 |
Filed Date | 2016-12-08 |
United States Patent
Application |
20160359403 |
Kind Code |
A1 |
Werner; Antonius Jacobus Johannes ;
et al. |
December 8, 2016 |
BJT DRIVER WITH DYNAMIC ADJUSTMENT OF STORAGE TIME VERSUS INPUT
LINE VOLTAGE VARIATIONS
Abstract
A power converter controller includes a storage time reference
circuit to generate a storage time reference signal in response to
an input voltage signal. A first comparator generates a collector
off signal in response to a current sense signal of a BJT and a
collector off reference threshold signal. A storage time regulator
circuit generates a base off reference threshold signal in response
to the storage time reference signal and the collector off signal.
A second comparator generates a base off signal in response to the
current sense signal and a base off reference threshold signal. A
driver circuit controls switching of the BJT in response to an
output voltage signal, discontinues charging a base terminal of the
BJT in response to the base off signal, and starts discharging the
base terminal of the BJT in response to the collector off signal
during a switching cycle of the BJT.
Inventors: |
Werner; Antonius Jacobus
Johannes; (Cambridge, GB) ; Bhasin; Manoj;
(Cambridge, GB) ; Waterson; Matthew David;
(Cambridge, GB) ; Lefedjiev; Adrian Kirilov;
(Gamlingay, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Power Integrations Limited |
Grand Cayman |
|
KY |
|
|
Family ID: |
57452370 |
Appl. No.: |
14/732413 |
Filed: |
June 5, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M 2001/0003 20130101;
H03K 17/04126 20130101; H02M 3/33523 20130101; H02M 3/33507
20130101; H02M 1/08 20130101; H03K 17/14 20130101; H02M 2001/0022
20130101 |
International
Class: |
H02M 1/00 20060101
H02M001/00; H02M 3/335 20060101 H02M003/335 |
Claims
1. A controller for use in a power converter, comprising: a storage
time reference circuit coupled to receive an input voltage signal
responsive to an input voltage of the power converter to generate a
storage time reference signal in response to the input voltage
signal; a first comparator coupled to receive a current sense
signal representative of a switch current of a bipolar junction
transistor (BJT) power switch, wherein the first comparator is
coupled to generate a collector off signal in response to a first
comparison of the current sense signal and a collector off
reference threshold signal; a storage time regulator circuit
coupled to generate a base off reference threshold signal in
response to the storage time reference signal and the collector off
signal; a second comparator coupled to receive the current sense
signal and the base off reference threshold signal, wherein the
second comparator is coupled to generate a base off signal in
response to a second comparison of the current sense signal and the
base off reference threshold signal; and a driver circuit coupled
to control switching of the BJT power switch in response to an
output voltage signal responsive to an output voltage of the power
converter to regulate a transfer of energy from an input of the
power converter to an output of the power converter, wherein the
driver circuit is further coupled to discontinue charging a base
terminal of the BJT power switch in response to the base off
signal, and wherein the driver circuit is further coupled to start
discharging the base terminal of the BJT power switch in response
to the collector off signal during a switching cycle of the BJT
power switch.
2. The controller of claim 1 further comprising an output regulator
circuit coupled to receive a feedback signal of the power
converter, wherein the output regulator is coupled to generate the
output voltage signal in response to the feedback signal.
3. The controller of claim 1 further comprising an input voltage
modeling circuit coupled to receive a feedback signal of the power
converter, wherein at least one portion of the feedback signal
represents the input voltage of the power converter and wherein the
input voltage modeling circuit is coupled to generate the input
voltage signal in response to the feedback signal.
4. The controller of claim 3 further comprising a latch coupled to
generate the input voltage signal in response to the feedback
signal, wherein the input voltage signal is a latched input voltage
signal representative of the input voltage of the power converter
in each switching cycle of the BJT power switch.
5. The controller of claim 1 wherein the driver circuit further
comprises: a current source coupled to provide a base drive
current; and a first switch coupled between the current source and
the base terminal of the BJT power switch, wherein the driver
circuit is coupled to turn on the first switch to charge the base
terminal of the BJT power switch with the base drive current, and
wherein the driver circuit is coupled to turn off the first switch
to discontinue charging the base terminal of the BJT power switch
with the base drive current.
6. The controller of claim 1 wherein the driver circuit further
comprises a variable current source coupled to provide a variable
base drive current to the base terminal of the BJT power switch,
wherein the variable base drive current varies from zero to a
desired level of base current.
7. The controller of claim 5 wherein the driver circuit further
comprises a second switch coupled between the base terminal of the
BJT power switch and a ground terminal, wherein the driver circuit
is coupled to turn on the second switch to start discharging the
base terminal of the BJT power switch.
8. The controller of claim 7 wherein the driver circuit further
comprises a third switch coupled to the BJT power switch, wherein
the driver circuit is coupled to turn on the third switch to
conduct the switch current of the BJT power switch to a current
sense resistor coupled to provide the current sense signal.
9. The controller of claim 8 wherein the ground terminal is further
coupled between the third switch and the current sense
resistor.
10. The controller of claim 1 wherein the storage time reference
circuit is further coupled to adjust the storage time reference
signal in response to variations in the input voltage signal.
11. The controller of claim 1 further comprising an input current
peak regulator circuit coupled to generate the collector off
reference threshold signal in response to the current sense
signal.
12. A power converter, comprising: an energy transfer element
coupled between an input of the power converter and an output of
the power converter; a bipolar junction transistor (BJT) power
switch coupled to the input of the power converter and the energy
transfer element; and a controller coupled to control switching of
the BJT power switch to regulate a transfer of energy from the
input of the power converter to the output of the power converter
through the energy transfer element, the controller including: a
storage time reference circuit coupled to receive an input voltage
signal responsive to an input voltage of the power converter to
generate a storage time reference signal representative of a BJT
power switch storage time; a first comparator coupled to receive a
current sense signal representative of a switch current of the BJT
power switch, wherein the first comparator is coupled to generate a
collector off signal in response to a first comparison of the
current sense signal and a collector off reference threshold
signal; a storage time regulator circuit coupled to generate a base
off reference threshold signal in response to the storage time
reference signal and the collector off signal; a second comparator
coupled to receive the current sense signal and the base off
reference threshold signal, wherein the second comparator is
coupled to generate a base off signal in response to a second
comparison of the current sense signal and the base off reference
threshold signal; and a driver circuit coupled to control the
switching of the BJT power switch in response to an output voltage
signal responsive to an output voltage of the power converter,
wherein the driver circuit is further coupled to discontinue
charging a base terminal of the BJT power switch in response to the
base off signal, and wherein the driver circuit is further coupled
to start discharging the base terminal of the BJT power switch in
response to the collector off signal during a switching cycle of
the BJT power switch.
13. The power converter of claim 12 wherein the energy transfer
element comprises: a first winding coupled to the input of the
power converter; a second winding coupled to the output of the
power converter; and a third winding coupled to provide a feedback
signal.
14. The power converter of claim 13 wherein the controller further
comprises an output regulator circuit coupled to receive the
feedback signal, wherein the output regulator is coupled to
generate the output voltage signal in response to the feedback
signal.
15. The power converter of claim 13 wherein the controller further
comprises an input voltage modeling circuit coupled to receive the
feedback signal, wherein at least one portion of the feedback
signal represents the input voltage of the power converter and
wherein the input voltage modeling circuit is coupled to generate
the input voltage signal in response to the feedback signal.
16. The power converter of claim 15 wherein the controller further
comprises a latch coupled to generate the input voltage signal in
response to the feedback signal, wherein the input voltage signal
is a latched input voltage signal representative of the input
voltage of the power converter of the BJT power switch.
17. The power converter of claim 12 wherein the driver circuit
further comprises: a current source coupled to provide a base drive
current; and a first switch coupled between the current source and
the base terminal of the BJT power switch, wherein the driver
circuit is coupled to turn on the first switch to charge the base
terminal of the BJT power switch with the base drive current, and
wherein the driver circuit is coupled to turn off the first switch
to discontinue charging the base terminal of the BJT power switch
with the base drive current.
18. The power converter of claim 17 wherein the driver circuit
further comprises a second switch coupled between the base terminal
of the BJT power switch and a ground terminal, wherein the driver
circuit is coupled to turn on the second switch to start
discharging the base terminal of the BJT power switch.
19. The power converter of claim 18 wherein the driver circuit
further comprises a third switch coupled to the BJT power switch,
wherein the driver circuit is coupled to turn on the third switch
to conduct the switch current of the BJT power switch to a current
sense resistor coupled to provide the current sense signal.
20. The power converter of claim 19 wherein the ground terminal is
further coupled between the third switch and the current sense
resistor.
21. The power converter of claim 12 wherein the storage time
reference circuit is further coupled to adjust the storage time
reference signal in response to variations in the input voltage
signal.
22. The power converter of claim 12 wherein the controller further
comprises an input current peak regulator circuit coupled to
generate the collector off reference threshold signal in response
to the current sense signal.
Description
BACKGROUND INFORMATION
[0001] Field of the Disclosure
[0002] The present invention relates generally to switched mode
power converters utilizing a Bipolar Junction Transistor (BJT) as a
switching element. More specifically, the present invention is
directed to the measurement and prediction of the BJT storage time
to provide a sufficient turn-off delay time for the improved
performance of a power converter.
[0003] Background
[0004] Electronic devices (such as cell phones, tablets, laptops,
etc.) use power to operate. Switched mode power converters are
commonly used due to their high efficiency, small size, and low
weight to power many of today's electronics. Conventional wall
sockets provide a high voltage alternating current. In a switching
power converter, a high voltage alternating current (AC), 50 or 60
Hz, input is converted through high frequency (HF) switching of a
switching element with controlled on and off states to provide a
well-regulated direct current (DC) output through an energy
transfer element to a load. The desired output is provided by
varying the duty cycle (ratio of the on-time to the total switching
period, known as pulse width modulation (PWM), varying the
switching frequency, which is known as pulse frequency modulation
(PFM), or by skipping some switching pulses per the load change
requirement, which is known as on-off control.
[0005] With stringent energy saving regulations for power
converters, there are continuing efforts to provide improved
operation and high efficiency in power converters. One important
parameter in an improved and efficient power converter is an
optimized switching function. Switching elements of the power
converter affect the efficiency of the power converter by
contributing to both the conduction loss and switching loss, which
form a major part of the power loss in the power converter.
[0006] MOSFET, BJT, IGBT or other types of semiconductor switches
may be used in switched mode power converters as a switching
element. Each of these types of electronic/semiconductor switches
may require specific driving provisions for efficient performance.
BJT switches are fast and efficient devices for switching. However,
due to their junction stored charge, BJT switches require special
provisions in order to have an efficient turn off.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Non-limiting and non-exhaustive embodiments of the present
invention are described with reference to the following figures,
wherein like reference numerals refer to like parts throughout the
various views unless otherwise specified.
[0008] FIG. 1 is a block diagram illustrating one general example
of a power converter based on the teachings of the present
invention utilizing a BJT controller with dynamic storage time
reference.
[0009] FIG. 2 is an example graph illustrating examples of ambient
temperature rise of a BJT versus storage time with low and high
input line voltages.
[0010] FIG. 3 illustrates interconnections of example BJT
controller blocks with a dynamic storage time reference in
accordance with the teachings of the present invention.
[0011] FIG. 4A is a graph illustrating waveforms and relationships
between example signals with a low line for a BJT controller blocks
with dynamic storage time reference in accordance with the
teachings of the present invention.
[0012] FIG. 4B is a graph illustrating waveforms and relationships
between example signals with a high line for a BJT controller
blocks with dynamic storage time reference in accordance with the
teachings of the present invention.
[0013] Corresponding reference characters indicate corresponding
components throughout the several views of the drawings. Skilled
artisans will appreciate that elements in the figures are
illustrated for simplicity and clarity and have not necessarily
been drawn to scale. For example, the dimensions of some of the
elements in the figures may be exaggerated relative to other
elements to help to improve understanding of various embodiments of
the present invention. Also, common but well-understood elements
that are useful or necessary in a commercially feasible embodiment
are often not depicted in order to facilitate a less obstructed
view of these various embodiments of the present invention.
DETAILED DESCRIPTION
[0014] In the following description, numerous specific details are
set forth in order to provide a thorough understanding of the
present invention. It will be apparent, however, to one having
ordinary skill in the art that the specific detail need not be
employed to practice the present invention. In other instances,
well-known materials or methods have not been described in detail
in order to avoid obscuring the present invention.
[0015] Reference throughout this specification to "one embodiment",
"an embodiment", "one example" or "an example" means that a
particular feature, structure or characteristic described in
connection with the embodiment or example is included in at least
one embodiment of the present invention. Thus, appearances of the
phrases "in one embodiment", "in an embodiment", "one example" or
"an example" in various places throughout this specification are
not necessarily all referring to the same embodiment or example.
Furthermore, the particular features, structures or characteristics
may be combined in any suitable combinations and/or subcombinations
in one or more embodiments or examples. Particular features,
structures or characteristics may be included in an integrated
circuit, an electronic circuit, a combinational logic circuit, or
other suitable components that provide the described functionality.
In addition, it is appreciated that the figures provided herewith
are for explanation purposes to persons ordinarily skilled in the
art and that the drawings are not necessarily drawn to scale.
[0016] As will be discussed, example power converters utilizing a
BJT power switch as a switching element with improved operation and
performance are disclosed. In one example, an improved controller
block for driving a BJT power switch element of a power converter
is introduced. The input line voltage is dynamically monitored and
modeled, and a storage time reference is generated in response to
the input line voltage. In the example, the BJT base turn off and
storage time of the BJT are dynamically adjusted each switching
cycle in response to the storage time reference to insert a
controlled BJT turn off delay in each switching cycle in response
to a dynamically derived BJT storage time reference in accordance
with the teachings of the present invention.
[0017] For instance, in one example, a controller block is
disclosed with dynamic adjustment of the BJT storage time reference
to drive a BJT switching element of a power converter that
optimizes or enhances the BJT switching performance, reduces the
switching loss and avoids or reduces the temperature rise of the
BJT. The controller block monitors or models the input line voltage
each switching cycle and generates references and thresholds for
the collector current and base current turn off. In one example,
the BJT driver in the controller block includes a base drive switch
and an emitter drive switch to be controlled individually through
the controller. A storage time reference is generated in response
to the input line voltage. The BJT base turn off and storage time
of the BJT is dynamically adjusted in each switching cycle in
response to the storage time reference. A controlled BJT turn off
delay is achieved in each switching cycle based on the dynamically
derived BJT storage time reference.
[0018] In an example of typical power converter illustrated in FIG.
1, the switching element 130 is coupled to the energy transfer
element, transformer T1 140, which in a flyback power converter is
a coupled inductor acting like a transformer, and is controlled by
a controller 120 that includes the Dynamic Storage Time Reference
Adjustment function in accordance with the teachings of the present
invention. The AC line V.sub.AC 102 is coupled to the full bridge
rectifier 104 that generates rectified voltage 105 to the power
converter. In an example in which there is no input bulk capacitor,
the full wave rectified voltage keeps the half sinusoidal waveform
V.sub.RECT 106 applied to the power converter through the input
filter 108, which includes inductor 113, and capacitors 112 and 114
as shown. The full wave rectified input voltage V.sub.IN 110 is
applied to the primary side of power converter. The primary winding
141 of transformer T1 140 is coupled to the input line, and
secondary winding 142 of transformer T1 140 is coupled to the
output circuitry 150, which in example illustrated in FIG. 1
includes a rectifier, which in the depicted example is implemented
with a fast Schottky diode 152, and a bulk filter capacitor C.sub.O
153 that generates the output DC voltage V.sub.O 156 across the
load 155 with output current I.sub.O 154.
[0019] In the illustrated example, output regulation is provided
through processing of the feedback from the output. The feedback
signal from the output may be provided through an isolated or
non-isolated sense circuit. When the feedback is referenced to the
secondary ground, it is referred as the secondary control. In some
power converters, the output sense may be extracted indirectly from
an auxiliary winding magnetically coupled to the output/secondary
winding so that the feedback signal may be referenced to the
primary ground, and is therefore referred to as the primary
control. The auxiliary winding may also provide operating power for
controller, and is sometimes referred to as a bias or bypass
winding.
[0020] In example depicted in FIG. 1, the output ground/reference
151 is isolated from input ground/reference 101. A third/auxiliary
winding 143 on the magnetic core of transformer T1 140 generates a
supply voltage across the supply terminal (bypass pin) BP 125 of
the controller 120 through a rectifier diode 145 and a filter
capacitor C.sub.AUX 148. Auxiliary winding 143 is referenced to the
primary ground 101 that is coupled to the GND terminal 121 of the
controller 120. The feedback information for regulating output,
through a resistive divider including resistors 146 and 147, is
retrieved indirectly from the auxiliary winding 143 coupled to
feedback terminal FB 122 of the controller 120. In one example, the
feedback information could be retrieved without scaling down
through the resistive divider as illustrated in FIG. 3, depending
on the primary to auxiliary windings turns ratio (e.g.,
N.sub.WAUX/N.sub.W1). In one example, the auxiliary winding
W.sub.AUX 143 is an anti-direction winding compared to the primary
winding W1 141, and provides a non-rectified AC induced voltage to
the FB terminal 122 of the controller 120.
[0021] In the depicted example, the input and output voltage
detection is monitored through the AC induced voltage in the
auxiliary winding W.sub.AUX, which is wound on the energy transfer
element T1 transformer in an anti-direction relative to the primary
winding W1. During the on-time when the BJT switch is conducting,
the negative voltage induced in the auxiliary winding W.sub.AUX
represents the input voltage. During off-time when the BJT switch
is not conducting, the induced positive voltage in the auxiliary
winding W.sub.AUX, as the FB signal, represents the output voltage
of the power converter. It is appreciated that in discontinuous
conduction mode (DCM) operation when the induced voltage in the
auxiliary winding W.sub.AUX drops towards zero, the idle
oscillations in the voltage that occur due to the parasitic
capacitances may go to the negative direction as well. In another
example, it is appreciated that the input voltage of power
converter could be monitored by measuring a required current
injected through an internal current source to clamp the negative
portions of the induced AC voltage in the auxiliary winding
W.sub.AUX 143 to zero.
[0022] The emitter and base terminals of the BJT switching element
130 are coupled to the terminals ED 126 and BD 127 of the
controller 120, respectively. Current 137 is sensed on the primary
return line through the sense resistor R.sub.CS 136. In the
example, the sensed current 137 is represented with the voltage
drop on sense resistor R.sub.CS, which is coupled to be received on
the terminal CS 128 of the controller 120. In the example, the
voltage drop on sense resistor R.sub.CS is with respect to the
primary ground/reference 101, and is therefore negative as
illustrated in FIG. 4A (460A) and FIG. 4B (460B). In the example,
the base terminal of the BJT switching element 130 is coupled
through a pull up resistor 132 to the input voltage. In one
example, the emitter terminal is coupled through ED 126 through an
internal switch of the controller 120, which is illustrated and
described in further detail below in FIG. 3 (switch 388), is
coupled to the primary ground/reference 101 and current sense
resistor R.sub.CS 136.
[0023] FIG. 2 is an example graph that illustrates the benefits of
utilizing a dynamic adjustment in accordance with the teachings of
the present invention of the storage time reference in a BJT driver
versus the input voltage. As shown, FIG. 2 illustrates temperature
rise vs. storage time for two different types of BJTs at low line
and high line voltage examples. The graph of FIG. 2 shows on the
vertical y-axis 220 the temperature rise of case to ambient, in
degrees Celsius [.degree. C.], for two different types of BJTs
(Type 1 and type 2) versus their storage time in nanoseconds [ns]
along the horizontal x-axis 210.
[0024] Graphs 230 and 240 are test results at high input line
voltage (e.g., 220 V.sub.AC) for two different types of BJT
transistors referred as type 1 and type 2 respectively. Similarly
graphs 250 and 260 are the test results in low input line voltage
(e.g., 110 V.sub.AC) for the same BJT transistors of type 1 and
type 2 respectively.
[0025] These test results confirm that in high line if the
adjustment of the storage time reference is not performed in
accordance with the teachings of the present invention, that the
temperature rise of the case to ambient for both types of the BJTs
due to the extra switching loss will be higher. As will be
discussed, examples in accordance with the teachings of the present
invention utilize measurements of the storage time of a BJT that is
used as a switching element in a power converter, and adjust the
storage time reference versus the input line voltage to provide
improved performance.
[0026] In test results illustrated in FIG. 2, the effect of a
non-adjusted storage time reference in temperature rise (case to
ambient) is shown for two types of BJTs that illustrate the benefit
of a BJT storage time reference adjustment versus input line
variations in accordance with the teachings of the present
invention. As will be discussed, a new controller block in
accordance with the teachings of the present invention provides
compensation with dynamic adjustment of the BJT storage time
reference versus input line variations.
[0027] To illustrate, FIG. 3 shows generally a schematic of an
example power converter, as well as the internal block
interconnections of an example controller for a BJT switching
device of the power converter, in accordance with the teachings of
the present invention. As will be described, the internal block
interconnections of the illustrated controller provide input line
voltage monitoring and modeling, measurement of the storage time in
each switching cycle, and dynamic adjustment of the storage time
reference in accordance with the teachings of the present
invention. In particular, in one example, power converter 300
includes a controller 320 that includes internal blocks for input
line voltage monitoring/modeling, storage time measurement in each
switching cycle, and dynamic adjustment of the storage time
reference.
[0028] As shown in the depicted example, power converter 300
includes an energy transfer element 340, which in one example is a
high frequency transformer or coupled inductor, having a first
winding (e.g., primary winding) 341 and a second winding (e.g.,
secondary winding) 342 coupled between an input and an output of
power converter 300. As shown in FIG. 3, the input of power
converter 300 is coupled to receive an input voltage V.sub.IN 310.
Energy is transferred through the energy transfer element 340 to an
output circuitry 350 referenced to secondary ground/reference 351
that is isolated from the primary ground/reference 301. The output
circuitry 350 as depicted in FIG. 1 may include a rectifier diode,
an output capacitor and a load coupled to the output that receives
an output voltage V.sub.O and an output current I.sub.O.
[0029] In the depicted example, the switching element 330 includes
a BJT and is coupled to the first winding 341 of the energy
transfer element 340. A controller 320 is coupled to control
switching of the BJT switch 330 with a base drive signal from
terminal BD 327 of controller 320 to control a transfer of energy
from the input of power converter to the output of power converter
through the energy transfer element 340 in response to a feedback
FB signal received on terminal 322 of the controller 320. In one
example, an output quantity of power converter 300 may be
representative of the output voltage V.sub.O, output current
I.sub.O, or a combination thereof, as shown for example in FIG.
1.
[0030] A third winding (e.g., auxiliary winding) 343 on the
magnetic core of energy transfer element (e.g., transformer) 340
generates a supply voltage through the rectifier diode D.sub.AUX
345 and a filter capacitor C.sub.AUX 348 across the supply terminal
(e.g., bypass pin) BP 325 of the controller 320 that is referenced
to the primary ground/reference 301, coupled to GND terminal 321 of
the controller 320. In one example, the regulation of the output is
responsive to the feedback signal retrieved from the non-rectified
voltage on the auxiliary winding 343 that is coupled to the
feedback terminal FB 322 of the controller 320. In example
schematic illustrated in FIG. 3 in comparison to the example
schematic of FIG. 1, there is no scaling down resistive divider,
and the FB signal is based on the turns ratio of the primary to
auxiliary windings (e.g., N.sub.WAUX/N.sub.W1) and is directly
coupled to the controller terminal FB 322.
[0031] The emitter and base terminals of the BJT switching element
330 are coupled to the terminals ED 326 and BD 327 of the
controller 320 respectively. The BJT collector current 335 during
the conduction time of the BJT switching element 330 is conducted
through the ED terminal 326 of the controller 320 and through an
internal switch 388, which may be coupled to the ground terminal
GND 321 of the controller 320. The collector current passes through
the primary side return line and is sensed as the current 337
through the sense resistor R.sub.CS 336.
[0032] As mentioned above with respect to FIG. 1, the primary side
return line current 337 sensed on resistor R.sub.CS 336 that is
applied to terminal CS 328 of the controller 320 shows as a
negative signal with respect to the primary ground, which is
illustrated as signal V.sub.CS 460A in FIG. 4A, and in FIG. 4B as
V.sub.CS 460B).
[0033] As shown in the example depicted in FIG. 3, controller 320
processes multiple sensed and received input signals representative
of the various parameters of the power converter 300 and generates
a control signal BD 327 to control the on and off states of the BJT
switching element 330 to regulate the output of the power supply in
a closed loop. The FB signal on terminal FB 322 is received from
the auxiliary winding 343, which in the example is a non-rectified
AC pulse signal, as shown for example in FIG. 4A as FB signal 470A,
and in FIG. 4B as FB signal 470B. During the on-time when BJT is
conducting, the induced voltage in the auxiliary winding 343 is
negative, due to the anti-phase of the auxiliary winding 343 in
relation to the primary winding 341, and is representative of the
input voltage. The scale factor for the monitored input voltage may
be presented by V.sub.IN*N.sub.WAUX/N.sub.W1, where N.sub.W1 is the
number of winding turns of the primary winding, and N.sub.WAUX is
the number of winding turns of the auxiliary winding.
[0034] During the on-time, the secondary current is blocked by the
reverse biased output diode, which is illustrated for example in
FIG. 1 as D1 152. However, the increased flux in the magnetic core
stores the energy, and when the BJT switch turns off or stops
conducting, the output diode, which is illustrated for example in
FIG. 1 as D1 152, would be forward biased to transfer the stored
energy to the output load. The signal on FB terminal 322 during the
BJT off-time (e.g., when output diode D1 152 conducts) represents
the scaled output voltage, V.sub.O*N.sub.WAUX/N.sub.W2, where
N.sub.WAUX is the number of auxiliary winding turns, and N.sub.W2
is the number of secondary winding turns.
[0035] The output regulator block 360 in controller 320 receives
the AC feedback signal from terminal FB 322 and extracts the
positive half cycles that are representative of the output voltage
to regulate the output. The signal 361 from output regulator block
360 is coupled to be received by the BJT control unit 380. In one
example, the BJT control unit 380 is coupled to control the on and
off timing of the switches 384, 386 and 388 in the BJT driver 390
in response to the signal 361. It is appreciated that either the
on-time (e.g., duty cycle control, PWM) or the switching period
(e.g., frequency control, PFM) may be controlled to achieve a
regulated output versus load and input voltage variations.
[0036] The BJT driver 390 receives the supply voltage on the
V.sub.CC bus 391 from terminal BP 325 of the controller 320 coupled
to the rectified auxiliary voltage across the C.sub.AUX capacitor
348. The base drive current I.sub.BD is generated from V.sub.CC bus
391 through the controlled current source 382, which is controlled
by signal 381 from the BJT control unit 380. In one example,
current source 382 is a variable current source that provides a
variable current from zero to a desired level of base drive current
I.sub.BD. Switch 384, which is controlled by signal Q.sub.BA 383
from the BJT control unit 380, conducts the I.sub.BD current
through node M 392 and through BD terminal 327 to the base of BJT
330. In one example, switch 384 is optional in an example in which
the current source 382 is variable from zero to the desired base
drive current I.sub.BD. Pulse width of the control signal Q.sub.BA
383 defines duration of the base current to the BJT switch 330.
Switch 386 across node M 392 to ground GND 321 is controlled by
signal Q.sub.BG 385 and may couple the base of BJT 330 to GND 321
to provide a discharge path for the storage charge of BJT at
turn-off. The BJT drive signal from node M 392 is coupled to the
terminal BD 327 of the controller 320. The emitter of BJT 330 is
coupled to terminal ED 326 of the controller 320 and through a
switch 388 it is coupled to GND 321.
[0037] Switch 388 is controlled by the signal Q.sub.EG 387 from the
BJT control unit 380. Control signal Q.sub.EG 387 is complementary
of signal Q.sub.BG 385. For the duration of time that switch 386 is
open, switch 388 remains closed and conducts the BJT current 335 to
the current sense resistor R.sub.CS 336 on the primary return line.
The sensed current across the resistor R.sub.CS 336 is applied to
terminal CS 328. The input current I.sub.IN peak regulator block
373 receives the sensed current and limits the peak current in each
switching cycle against a predefined current limit threshold to
generate the signal Coff_Ref 375, which is a reference for the
collector turn off.
[0038] Signal Coff_Ref 375 on the positive input 374 of the current
comparator 376 is compared to the sensed current 377 on the
negative input of the current comparator and generates signal Coff
378 that may be used to define duration of the storage time. The
Coff signal 378 is fed back to the second input of the storage time
regulator block 368. The storage time regulator block 368 processes
combination of the two input signals, t.sub.ref 367 and Coff 378,
and generates signal Boff_Ref 369, which is a reference signal for
the base turn off. After the base switch 384 is turned off by
signal Q.sub.BA 381 going low, which is illustrated in FIG. 4A as
Q.sub.BA 410A, the collector current continues to rise until the
signal Q.sub.EG 387, which is illustrated in FIG. 4A as Q.sub.EG
430A, commands to turn off the emitter switch 388, which is
illustrated in FIG. 4A as time tst1 454A.
[0039] The storage time reference signal t.sub.ref 367 is generated
in response to the input voltage of the power converter. Signal
t.sub.ref 367 dynamically represents the input voltage to regulate
the storage time through the storage time regulator block 368.
Signal Coff 378 may be used to define the storage time that
represents the discharge time required for the stored charge in the
junction of BJT before its complete turn off. In the depicted
example, the BJT storage time is defined and measured through the
signal Coff in accordance with the teachings of the present
invention. The start point for storage time is when the emitter
switch 388 has turned off by signal Q.sub.EG 387 going low, which
is shown with signal 430A in FIG. 4A and is presented by the
intersection point tst1 454A in graph 450 in FIG. 4A. During the
storage discharge interval, as indicted in FIG. 4A at reference
numeral 447A, the collector current 450A due to the base discharge
current through switch 386, which is closed by signal 385 Q.sub.BG
going high in graph 420A of FIG. 4A, continues until time tst2,
which occurs at intersection 455A, at which time the collector
current 450A bends back towards zero as shown.
[0040] It is appreciated that when the emitter drive switch 388 is
turned off, the base to ground switch 386 is simultaneously turned
on by the signal Q.sub.BG 385 going high, which is indicated with
signal 420A in FIG. 4A, to discharge the BJT 330 junction storage
charge. When switch 388 disconnects the emitter current path, the
BJT 330 may completely turn off only after the storage time period,
which is indicated in FIG. 4A with reference numeral 447A. The
storage time is indicated with the intersections of Coff_Ref 453A
with the collector current 450A, between time tst1 454A to time
tst2 455A, at which time the collector current folds back towards
zero.
[0041] Signal "Boff_Ref" 369 is coupled to the positive input of
the comparator 370. The negative input receives the sensed
collector current as a voltage signal V.sub.CS on the terminal CS
328. The output signal Boff 372 of the comparator 370 would be
logic high as long as the sensed current signal V.sub.CS is lower
than Boff_Ref 369 and drops to logic low as soon as the sensed
collector current signal V.sub.CS hits the Boff_Ref 369 to turn off
the base current.
[0042] The AC feedback signal derived from terminal FB 322 is
received by the V.sub.IN model block 362, which is coupled in
parallel with the output regulator block 360 in FIG. 3 as shown. A
model of the input voltage that is generated by the V.sub.IN model
block 362 is buffered through driver 363. Modeling of the input
voltage may be as simple as extracting the negative portions of the
signal FB 322, or in another example by forcing a current out of
the example controller 320 during the negative portions to hold the
signal FB 322 node at zero, and measuring the forced current as a
representation of the input voltage. The sampled input voltage may
then be latched through the sample latch block 364. It is
appreciated that even though the sample latch block 364 is
described in the example controller of FIG. 3, it is optional and
in other examples, the controller may function without latching the
sampled input voltage. The signal 365 output from sample latch
block 364 is representative of the input voltage, and is coupled to
be received by the storage time reference block 366. The storage
time reference block 366 generates the t.sub.ref signal 367
received by the storage time regulator block 368.
[0043] In one example controller 320 may be implemented in an
integrated circuit (IC) and the BJT 330 switching element may also
be monolithically or non-monolithically (e.g., hybrid) included in
the same IC.
[0044] FIG. 4A and FIG. 4B illustrate the sample waveforms
generated by the different function blocks of FIG. 3 at a low input
line voltage and a high input line voltage, respectively, to
illustrate the dynamic measurement and adjustment of the BJT
storage time versus the input voltage variations in accordance with
the teachings of the present invention. To avoid repetition, only
the description for the low input line voltage waveforms are
explained below in the graphs 400A of FIG. 4A. It is appreciated,
however, that all of the explanations for both graphs 400A of FIG.
4A and graphs 400B FIG. 4B are substantially similar, except that
for the high input line voltage the BJT conduction time (e.g.,
on-time) for the same power level would be shorter than the low
input line voltage.
[0045] In the example described in FIG. 4A, graphs 400A are
waveforms of the control signals utilized by a controller block for
a BJT driver with the dynamic adjustment of the storage time
reference versus the input line voltage variation in accordance
with the teachings of the present invention. Graphs Q.sub.BA 410,
Q.sub.BG 420, and Q.sub.EG 430 show the control signals for switch
384 (e.g., signal Q.sub.BA 383 in FIG. 3), switch 386 (e.g., signal
Q.sub.BG 385 in FIG. 3) and switch 388 (e.g., signal Q.sub.EG 387
in FIG. 3) inside the BJT driver 390. A logic high of each signal
means that switch is turned on (e.g., closed) and logic low means
that switch is turned off (e.g., opened).
[0046] The graph of base current I.sub.B 440A illustrates the BJT
base current from the controlled current source 382 and through
switch 384, which shows the positive injected base current in
portions 442A and 444A. The discharged current of the stored charge
in BJT junction during the storage time that is shown as the
negative portion 447A in graph of base current IB 440A, which
illustrates the current though the switch 386 as indicated in graph
Q.sub.BG 430A.
[0047] The graph of collector current I.sub.C 450A shows the BJT
collector current in positive direction and the graph of current
sense V.sub.CS 460A shows the sensed current signal V.sub.CS that
is measured across the sense resistor on the primary return line
that is negative in reference to the primary side controller
ground. It is appreciated that the turn on current spikes 457A or
467A on the collector current I.sub.C waveform 450A, and
consequently on the current sense signal V.sub.CS 460A, may happen
mostly due to the parasitic/stray capacitance of the transformer
windings.
[0048] In the graph of collector current I.sub.C 450A, the
reference thresholds for the base switch off (e.g., Boff_Ref, 451A)
and for the collector switch off (e.g., Coff_Ref, 453A) are
illustrated in comparison to the BJT collector current, which is
the on-time rising sloped current. These references or thresholds,
Boff_Ref 451A (e.g., Boff_Ref 369A in FIG. 3) and Coff_Ref 453A
(e.g., Coff_Ref, 375 in FIG. 3) define the switching signals for
the BJT driver. In FIG. 3, the BJT driver 390 through the BJT
control unit 380 generates the switching signals Q.sub.BA 383,
Q.sub.BG 385, and Q.sub.EG 387 for the BJT driver switches 384, 386
and 388 respectively. It should be mentioned that in an example in
accordance with the teachings of the present invention the pulse
width 492A is a controlled variable. For instance, in one example,
the pulse width 492A is controlled by modulating and changing the
Boff_Ref 451 reference. The Boff_Ref 451 reference determines the
pulse width 412A in graph Q.sub.BA 410A, which in turn determines
the on-time of the switch 383 and the amount of charge delivered to
the base of the BJT. The amount of charge delivered to the base of
the BJT in turn determines the required discharge time (e.g.,
portion 447A), and the signal Coff 490A determines the pulse width
of 492A. The signal Coff 490A is regulated so that the pulse width
492A is equal to the pulse 497A of the storage time reference
t.sub.ref 495A.
[0049] The graph of FB signal 470A illustrates the FB AC signal in
which the negative half cycle 472A represents the input line
voltage, and the positive half cycle 474A gives the output feedback
information. If BJT operation is in DCM, after the output current
drops to zero and remains almost zero 476A until the next switching
cycle starts.
[0050] The graph of transformer flux .PHI. 480A is an illustration
of the transformer magnetic flux. During the first half cycle of
BJT conduction period (e.g., on time), the transformer flux .PHI.
480A has a rising slope, and in the second half cycle when energy
is transferring to the output, transformer flux .PHI. 480A has a
falling slope. In DCM operation at the end of second half cycle
when the output current is dropped to zero and transfer of energy
is stopped, the transformer flux .PHI. 480A remains almost zero. It
is appreciated that even though not shown in graphs 470A or 480A,
when the transfer of energy is stopped, some idle ringing due to
resonant charge/discharge of the parasitic capacitances may be
observed.
[0051] The graph of current sense reference Boff 485A shows the
current sense reference signal Boff for the base current turn off
that goes to logic high as long as the BJT collector current Ic, or
the sense current signal V.sub.CS in the negative direction, is
higher than the Boff_Ref threshold.
[0052] The graph of Coff 490A shows the collector current turn off
signal Coff and indicates that the collector current has reached
the designated peak current threshold Coff_Ref. The pulse width of
the Coff signal 490A is a measure of the storage time. This signal
goes to logic high as long as the BJT collector current Ic, or the
sense current signal V.sub.CS in negative direction, is higher than
the Coff_Ref threshold (e.g., duration 492A between tst1 454A and
tst2 455A).
[0053] The graph of storage time reference t.sub.ref 495A
represents the storage time reference t.sub.ref with a pulse width
497A. This signal is generated in response to the input voltage of
the power converter (e.g., through blocks 362, 363, 364 and 366 in
FIG. 3). In each switching cycle, signal t.sub.ref 495A (e.g.,
t.sub.ref 367 in FIG. 3) in response to a latched value of the
input voltage model through the storage time regulator block 368
generates signal Boff_Ref 451A, which is the base turn off
reference threshold, to regulate the base turn off and the amount
of the charge delivered to the BJT base for an optimum switching of
the BJT power switch with the least turn off loss. The discharge
time or storage time is defined by the time interval between tst1
454A and tst2 455A that the BJT collector current I.sub.C 450A is
higher than the Coff_Ref reference threshold 453A (e.g., signal
Coff 490A high, duration 492A). In each switching cycle the
discharge time follows (e.g., remains equal to) the t.sub.ref pulse
duration 497A.
[0054] In operation, referring to FIG. 3 and FIG. 4A, in each
switching cycle T.sub.SW 401A, signal 410A Q.sub.BA at the start of
a switching cycle is logic high, and switch 384 is closed
conducting the base drive controlled current I.sub.BD 382 to the
base of the BJT switch 330 through the node M 392 and terminal BD
327 of the controller 320. The amount of the base current I.sub.BD
382 is controlled through signal 381 from BJT control unit 380.
When the Q.sub.BA 410A signal is logic high (e.g., switch 384 is
closed), the Q.sub.BG 420A signal is logic low (e.g., switch 386 is
open) to prevent any discharge from the base of the BJT 330. The
Q.sub.EG 430A signal remains logic high and switch 388 is closed to
conduct the collector current 335, or its equivalent current 337 to
the return line through the sense resistor 336.
[0055] The base current is represented by the signal I.sub.B 440A,
where the amount of the base current at the start of each BJT
switch on time for a duration 442A goes to a higher level to cover
the junction capacitor inrush charge. After the junction capacitor
inrush, the base current drops to a lower level for the rest of the
BJT on-time 444A. At the end of duration 412A, the Q.sub.BA 410A
signal drops from high to low. The base drive current turn off,
which is the end of duration 412A on graph 410A, is defined on the
graph of collector current I.sub.C 450A by the intersection point
452A of the collector current I.sub.C 450A and Boff_Ref 451A, which
is the Boff_Ref 369 signal in FIG. 3. From this point, no current
is injected to the BJT base, as shown for example with signal
Q.sub.BA going low, switch 384 opening, and base current I.sub.B
440A dropping to zero. However, due to the BJT stored charge, the
collector current I.sub.C 450A continues rising for a period of
446A up to the intersection point 454A with the Coff_Ref 453A,
which is signal 375 in FIG. 3. The intersection point 454A is
defined by the input current peak regulator, which is I.sub.IN peak
regulator block 373 as described in FIG. 3. From this point, the
stored charge in the BJT junction starts to discharge, and base
current 440A goes negative for a discharge time duration 447A. The
discharge time duration 447A is defined by the time duration from
time tst1 (454A) to time tst2 (455A).
[0056] The time tst1 454A is when the Q.sub.BG 420A signal and the
Q.sub.EG 430A signal change their states, which is when Q.sub.BG
goes from low to high closing the switch 386, and Q.sub.EG goes
from high to low opening the switch 388. However, due to discharge
of the storage charge through switch 386, the collector current
450A continues increasing above the Coff_Ref 453A until the end of
the discharge time, at which time it folds back falling towards the
zero. The time tst2 455A is when all the stored charge in the BJT
junction has discharged and the collector current 450A has dropped
back below the Coff_Ref 453A. It is appreciated that the current
sense signal V.sub.SC 460A, which is the voltage drop of the
collector current 337 across the sense resistor 336 in FIG. 3, is
only a negative representation of the collector current 450A.
[0057] At time tst1 454A the output of the comparator 376, which is
the Coff 378 signal in FIG. 3, goes high until time tst2 455A, at
which time it drops back to logic low. The pulse width 492A of the
signal Coff 490A dynamically follows, or remains equal to, the
pulse width 497A of the storage time reference signal t.sub.ref
495A represents the required discharge time and provides an easy
dynamic and accurate measure to adjust the BJT storage time in each
switching cycle in accordance with the teachings of the present
invention.
[0058] Like FIG. 4A, FIG. 4B also illustrates the sample waveforms
generated by the different function blocks of FIG. 3. In
particular, FIG. 4A illustrates the sample waveforms at a low input
line voltage, while FIG. 4B illustrates the sample waveforms
generated by the different function blocks of FIG. 3 at a high
input line voltage. It is appreciated that the description of the
sample waveforms illustrated FIG. 4B are similar to the
descriptions provided with respect to FIG. 4A, except that for the
high line input voltage, the conduction time and storage time
associated with the BJT in the sample waveforms in FIG. 4B is
shorter at the high line input voltage compared to the low line
input voltage.
[0059] It is also appreciated that for the simplicity with respect
to the the graphs illustrated in FIG. 4A and FIG. 4B, that any
parasitic ringing has not been illustrated and that in other
examples, parasitic ringing may occur due to the resonance of
parasitic capacitances and inductances on the circuit board, which
may cause some turn on and turn off oscillations.
[0060] The above description of illustrated examples of the present
invention, including what is described in the Abstract, are not
intended to be exhaustive or to be limitation to the precise forms
disclosed. While specific embodiments of, and examples for, the
invention are described herein for illustrative purposes, various
equivalent modifications are possible without departing from the
broader spirit and scope of the present invention. Indeed, it is
appreciated that the specific example voltages, currents,
frequencies, power range values, times, etc., are provided for
explanation purposes and that other values may also be employed in
other embodiments and examples in accordance with the teachings of
the present invention.
* * * * *