U.S. patent application number 13/973168 was filed with the patent office on 2014-02-27 for ac-to-dc power converter and control method and control integrated circuit thereof.
This patent application is currently assigned to Richtek Technology Corporation. The applicant listed for this patent is Richteck Technology Corporation. Invention is credited to Isaac Y. CHEN, Yu-Chang CHEN, Jung-Pei CHENG, Jyun-Che HO, Jiun-Hung PAN, Chien-Fu TANG.
Application Number | 20140056036 13/973168 |
Document ID | / |
Family ID | 50147878 |
Filed Date | 2014-02-27 |
United States Patent
Application |
20140056036 |
Kind Code |
A1 |
PAN; Jiun-Hung ; et
al. |
February 27, 2014 |
AC-TO-DC POWER CONVERTER AND CONTROL METHOD AND CONTROL INTEGRATED
CIRCUIT THEREOF
Abstract
An AC-to-DC power converter with a BJT as a power switch can set
a base current of the BJT by a current setting resistor which is in
the outside of a control integrated circuit. Since an output
current and a recovery current of the BJT are injected into a
sensing resistor, the AC-to-DC power converter can correctly detect
an inductor current thereof from the sensing resistor.
Inventors: |
PAN; Jiun-Hung; (Taipei
City, TW) ; TANG; Chien-Fu; (Hsinchu City, TW)
; HO; Jyun-Che; (Xikou Township, TW) ; CHEN; Isaac
Y.; (Jubei City, TW) ; CHEN; Yu-Chang; (Jiji
Township, TW) ; CHENG; Jung-Pei; (Huatan Township,
TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Richteck Technology Corporation |
Chupei City |
|
TW |
|
|
Assignee: |
Richtek Technology
Corporation
Chupei City
TW
|
Family ID: |
50147878 |
Appl. No.: |
13/973168 |
Filed: |
August 22, 2013 |
Current U.S.
Class: |
363/21.12 |
Current CPC
Class: |
H02M 2001/0009 20130101;
H02M 7/217 20130101; H02M 3/156 20130101; H02M 3/157 20130101; H02M
1/08 20130101; H02M 3/33515 20130101; H02M 3/33507 20130101; H02M
3/33523 20130101 |
Class at
Publication: |
363/21.12 |
International
Class: |
H02M 7/217 20060101
H02M007/217 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 23, 2012 |
TW |
101130683 |
Claims
1. An AC-to-DC power converter comprising: a rectifier circuit
configured to rectify an AC voltage to generate an input voltage; a
bipolar junction transistor connected to the rectifier circuit,
and, configured to, when being on, have an output terminal thereof
providing an output current; an inductor connected to the bipolar
junction transistor; a current-setting resistor; and a control
integrated circuit having a first pin connected to the bipolar
junction transistor for switching the bipolar junction transistor,
and having a second pin connected to the current-setting resistor,
wherein the control integrated circuit includes: a
base-current-setting circuit connected to the second pin, for
detecting a resistance of the current-setting resistor to generate
a current-controlling signal; and a current source connected to the
base-current-setting circuit, and, configured to, when the bipolar
junction transistor is on, generate a base current for a base of
the bipolar junction transistor according to the
current-controlling signal.
2. The AC-to-DC power converter as recited in claim 1, further
comprising a sensing resistor that has a first terminal connected
to a third pin of the control integrated circuit and a second
terminal connected to the second pin through the current-setting
resistor, wherein the sensing resistor determines a voltage of the
third pin according to the output current and a recovery current of
the bipolar junction transistor, and the voltage of the third pin
is used to determine a reference potential for the control
integrated circuit.
3. The AC-to-DC power converter as recited in claim 2, wherein the
control integrated circuit further comprising a current sensor
connected to the second pin, and configured to determine a value of
an inductor current on the inductor according to a relative voltage
between the second pin and the third pin, and generate a
current-sensing signal when the relative voltage reaches a
predetermined threshold to turn off the bipolar junction
transistor.
4. The AC-to-DC power converter as recited in claim 2, wherein a
voltage of the second pin is equal to a sum of a voltage drop in
the current-setting resistor and a voltage at the second terminal
of the sensing resistor.
5. The AC-to-DC power converter as recited in claim 4, wherein the
voltage drop in the current-setting resistor varies with the input
voltage when the inductor current is raising.
6. The AC-to-DC power converter as recited in claim 1, wherein the
base-current-setting circuit, when the AC-to-DC power converter is
activated, detects the resistance of the current-setting resistor
to generate and store the current-controlling signal.
7. The AC-to-DC power converter as recited in claim 1, wherein the
base-current-setting circuit, when the bipolar junction transistor
is turned off, detects the resistance of the current-setting
resistor to generate and store the current-controlling signal.
8. The AC-to-DC power converter as recited in claim 1, wherein the
base-current-setting circuit comprises: a detector connected to the
second pin, for detecting the resistance of the current-setting
resistor to generate a detecting signal; a storage unit connected
to the detector, for storing the detecting signal; and a translate
circuit connected to the storage unit, for converting the detecting
signal stored in the storage unit into the current-controlling
signal.
9. The AC-to-DC power converter as recited in claim 8, wherein the
translate circuit, when the bipolar junction transistor is on,
adjusts the current-controlling signal according to a voltage of
the second pin.
10. The AC-to-DC power converter as recited in claim 1, wherein the
base-current-setting circuit comprises: a detector connected to the
second pin, for detecting the resistance of the current-setting
resistor to generate the current-controlling signal; and a storage
unit connected to the detector and the current source, for storing
and outputting the current-controlling signal.
11. An AC-to-DC power converter comprising: a rectifier circuit
configured to rectify an AC voltage to generate an input voltage; a
power switch connected to the rectifier circuit; an inductor
connected to the power switch; a sensing resistor connected to the
power switch, and configured to, according to a current of the
power switch, generate a first voltage at a first terminal thereof
and generate a second voltage at a second terminal thereof; a
shifting circuit connected to the second terminal of the sensing
resistor, for providing a third voltage to shift the second voltage
to generate a fourth voltage; and a control integrated circuit
having a first pin connected to the power switch for switching the
power switch, a second pin connected to the first terminal of the
sensing resistor, and a third pin connected to the shifting circuit
for, according to a relative voltage between the first voltage and
the fourth voltage, determining an inductor current of the
inductor.
12. The AC-to-DC power converter as recited in claim 11, wherein
the power switch comprises a MOSFET.
13. The AC-to-DC power converter as recited in claim 11, wherein
the power switch comprises a bipolar junction transistor.
14. The AC-to-DC power converter as recited in claim 13, wherein
when the bipolar junction transistor is turned off, a recovery
current thereof passes through the sensing resistor.
15. The AC-to-DC power converter as recited in claim 11, wherein
the third voltage varies with the input voltage.
16. The AC-to-DC power converter as recited in claim 11, wherein
the shifting circuit comprises: an auxiliary coil configured to
sense the input voltage to generate a fifth voltage; a first
resistor connected between the auxiliary coil and the third pin;
and a second resistor connected between the third pin and the
second terminal of the sensing resistor, wherein the first resistor
and the second resistor divide a voltage difference between the
fifth voltage and the second voltage to generate the third voltage;
wherein a resistance ratio between the first resistor and the
second resistor determines the third voltage and in turn the fourth
voltage.
17. A control integrated circuit of an AC-to-DC power converter,
the control integrated circuit serving to switch a bipolar junction
transistor to control an inductor current on an inductor and
comprising: a pin for connecting to a current-setting resistor; a
base-current-setting circuit connected to the pin, for detecting a
resistance of the current-setting resistor connected to the pin to
generate a current-controlling signal; and a current source
connected to the base-current-setting circuit, and configured to,
when the bipolar junction transistor is on, generate a base current
for a base of the bipolar junction transistor according to the
current-controlling signal.
18. The control integrated circuit as recited in claim 17, wherein
the base-current-setting circuit, when the AC-to-DC power converter
is activated, detects the resistance of the current-setting
resistor connected to the pin to generate and store the
current-controlling signal.
19. The control integrated circuit as recited in claim 17, wherein
the base-current-setting circuit, when the bipolar junction
transistor is turned off, detects the resistance of the
current-setting resistor connected to the pin to generate and store
the current-controlling signal.
20. The control integrated circuit as recited in claim 17, wherein
the base-current-setting circuit comprises: a detector connected to
the pin, for detecting the resistance of the current-setting
resistor connected to the pin to generate a detecting signal; a
storage unit connected to the detector, for storing the detecting
signal; and a translate circuit connected to the storage unit, for
converting the detecting signal stored in the storage unit into the
current-controlling signal.
21. The control integrated circuit as recited in claim 20, wherein
the translate circuit, when the bipolar junction transistor is on,
adjusts the current-controlling signal according to a voltage of
the pin.
22. The control integrated circuit as recited in claim 17, wherein
the base-current-setting circuit comprises: a detector connected to
the pin, for detecting the resistance of the current-setting
resistor connected to the pin to generate the current-controlling
signal; and a storage unit connected to the detector and the
current source, for storing and outputting the current-controlling
signal.
23. The control integrated circuit as recited in claim 17, further
comprising a current sensor connected to the pin, and configured to
determine a value of the inductor current according to a relative
voltage between voltage of the pin and a reference potential for
the control integrated circuit, and, when the relative voltage
reaches a predetermined threshold, generate a current-sensing
signal to turn off the bipolar junction transistor.
24. A control method of an AC-to-DC power converter, the AC-to-DC
power converter including a rectifier circuit configured to rectify
an AC voltage to generate and an input voltage and a control
integrated circuit configured to switch a bipolar junction
transistor to control an inductor current of an inductor, the
control method comprising the steps of: detecting a resistance of a
current-setting resistor to generate a current-controlling signal;
and determining a base current provided to the bipolar junction
transistor according to the current-controlling signal.
25. The control method as recited in claim 24, wherein the step of
detecting a resistance of a current-setting resistor to generate a
current-controlling signal comprises the step of detecting the
resistance of the current-setting resistor when the AC-to-DC power
converter is activated to generate and store the
current-controlling signal.
26. The control method as recited in claim 24, wherein the step of
detecting a resistance of a current-setting resistor to generate a
current-controlling signal comprises the step of detecting the
resistance of the current-setting resistor when the bipolar
junction transistor is turned off to generate and store the
current-controlling signal.
27. The control method as recited in claim 24, wherein the step of
detecting a resistance of a current-setting resistor to generate a
current-controlling signal comprises the steps of: detecting the
resistance of the current-setting resistor to generate a detecting
signal; storing the detecting signal; and converting the stored
detecting signal into the current-controlling signal.
28. The control method as recited in claim 24, wherein the step of
detecting a resistance of a current-setting resistor to generate a
current-controlling signal comprises the step of storing the
current-controlling signal.
29. The control method as recited in claim 24, further comprising
the step of adjusting the current-controlling signal according to a
voltage of the current-setting resistor when the bipolar junction
transistor is on.
30. The control method as recited in claim 24, further comprising
the steps of: when the bipolar junction transistor is on, providing
an output current at an output terminal of the bipolar junction
transistor to a sensing resistor, to generate a first voltage and a
second voltage at a first terminal and a second terminal of the
sensing resistor, respectively; providing a third voltage to shift
the second voltage to generate a fourth voltage; determining an
inductor current according to a relative voltage between the first
voltage and the fourth voltage; turning off the bipolar junction
transistor when the relative voltage reaches a predetermined
threshold; and providing a recovery current of the bipolar junction
transistor to the sensing resistor when the bipolar junction
transistor is turned off.
31. The control method as recited in claim 30, further comprising
the step of using the current-setting resistor to provide the third
voltage.
32. The control method as recited in claim 30, further comprising
the step of providing the third voltage varying with the input
voltage.
33. The control method as recited in claim 30, wherein the step of
providing the third voltage to shift the second voltage to generate
the fourth voltage comprises the steps of: sensing the input
voltage by an auxiliary coil to generate a fifth voltage; and using
a pair of serially-connected resistors between the auxiliary coil
and the second terminal of the sensing resistor to divide a voltage
difference between the fifth voltage and the second voltage to
generate the third voltage for shifting the second voltage and in
turn generating the fourth voltage; wherein a resistance ratio
between the serially-connected resistors determines the third
voltage to determine the fourth voltage.
34. A control method of an AC-to-DC power converter, the AC-to-DC
power converter including a rectifier circuit configured to rectify
an AC voltage to generate an input voltage and a control integrated
current configured to switch a power switch to control an inductor
current of an inductor, the control method comprising the steps of:
when the power switch is on, providing an output current at an
output terminal of the power switch to a sensing resistor, to
generate a first voltage and a second voltage at a first terminal
and a second terminal of the sensing resistor, respectively;
providing a third voltage for shifting the second voltage to
generate a fourth voltage; determining the inductor current
according to a relative voltage between the first voltage and the
fourth voltage; and turning off the power switch when the relative
voltage reaches a predetermined threshold.
35. The control method as recited in claim 34, further comprising
the step of using a MOSFET as the power switch.
36. The control method as recited in claim 34, further comprising
the step of using a bipolar junction transistor as the power
switch.
37. The control method as recited in claim 36, further comprising
the step of providing a recovery current of the bipolar junction
transistor to the sensing resistor when the bipolar junction
transistor is turned off.
38. The control method as recited in claim 34, further comprising
the step of providing the third voltage that varies with the input
voltage.
39. The control method as recited in claim 34, wherein the step of
providing a third voltage for shifting the second voltage to
generate a fourth voltage comprises the steps of: sensing the input
voltage by an auxiliary coil to generate a fifth voltage; and
dividing a voltage difference between the fifth voltage and the
second voltage by a pair of resistors connected in series between
the auxiliary coil and the second terminal of the sensing resistor,
to generate the third voltage for shifting the second voltage and
in turn generating the fourth voltage; wherein a resistance ratio
between the pair of resistors determines the third voltage and in
turn the fourth voltage.
Description
FIELD OF THE INVENTION
[0001] The present invention is related generally to an AC-to-DC
power converter and, more particularly, to an AC-to-DC power
converter with a bipolar junction transistor (BJT) as a power
switch.
BACKGROUND OF THE INVENTION
[0002] Recently, with the consideration of costs, in some AC-to-DC
power converters, a BJT is used instead of a
metal-oxide-semiconductor field-effect transistor (MOSFET) as the
power switch, such as those described in U.S. Pat. Nos. 8,045,348
and 7,961,484 and U.S. Pat. Application Publication No.
2010/0202165.
[0003] BJT driving technique includes two types, namely base
driving (BD) and emitter driving (ED). FIG. 1 shows an AC-to-DC
power converter using BD technique, in which a rectifier circuit 10
rectifies an alternating current (AC) voltage VAC to generate an
input voltage Vin, in a BJT Q1, a collector works as an input
terminal connected to an inductor Np, and an emitter works as an
output terminal connected to sensing resistor Rcs, and a control
integrated circuit (IC) 12 has a pin Output connected to a base of
the BJT Q1 and providing a base current Ib to switch the BJT Q1 to
convert the input voltage Vin into an output voltage V0. The
control IC 12 further has a pin Isense connected to a sensing
resistor Rcs for detecting an output current Ie of the BJT Q1. When
the BJT Q1 is on, the inductor current Ic of the inductor Np
raises. Ideally, the inductor current Ic is close to the current
Ie, so that the control IC 12 can determine the inductor current Ic
according to the voltage Vcs at the sensing resistor Rcs, and turn
off the BJT Q1 when the inductor current Ic reaches a predetermined
peak. In addition, the internal circuit of the control IC 12 can
also set the base current Ib according to the voltage Vcs. However,
the control IC 12 can only provide the base current Ib in a fixed
range. Once the required base current Ib is not within the fixed
range, the optimal performance becomes unachievable.
[0004] FIG. 2 shows an AC-to-DC power converter using another BD
technique, in which a rectifier circuit 10 rectifies an AC voltage
VAC to generate an input voltage Vin, a control IC 14 has a pin
Base connected to the base of a BJT Q1 to switch the BJT Q1 and
thereby convert the input voltage Vin into an output voltage V0,
and a current-setting resistor Rset is connected between pins VDD
and VDD-B. The current-setting resistor Rset generates a base
current Ib for the control IC 14 according to a voltage drop
therein. FIG. 3 shows the control IC 14 as shown in FIG. 2, which
includes switches SW1 and SW2 and a driver 16. When the driver 16
turns on the switch SW1 and turns off the switch SW2, as shown at
the time t1 in FIG. 4, the current-setting resistor Rset generates
a base current Ib for the base of the BJT Q1 to turn on the BJT Q1.
The increase of the inductor current Ic induces the increase of the
voltage Vcs of the sensing resistor Rcs. When the voltage Vcs
reaches a predetermined threshold, the driver 16 turns off the
switch SW1 and turns on the switch SW2 to turn off the BJT Q1, as
shown at the time t2 in FIG. 4. In this AC-to-DC power converter,
the base current Ib of the BJT Q1 is determined by the
current-setting resistor Rset outside the control IC 14, so a user
may select an appropriate current-setting resistor Rset for the
base current Ib as desired. However, an additional pin VDD-B is
needed for this purpose. Furthermore, one characteristic of BJT is
that when the BJT Q1 is turned off, the output current Ie of the
BJT Q1 ends, but BJT Q1 will generate a recovery current Irb that
flow to the base of the BJT Q1 from its collector. This causes the
inductor current Ic of the collector of the BJT Q1 remains going up
for a period of time after the current Ie ends, as happening during
the tome period between time points t2 and t3 in FIG. 4, making the
voltage Vcs of the sensing resistor Rcs unable to represent the
inductor current Ic, and hindering the control IC 14 from getting
the correct inductor current Ic by referring to the voltage
Vcs.
[0005] FIG. 5 shows an AC-to-DC power converter using ED technique,
in which a rectifier circuit 10 rectifies an AC voltage VAC to
generate an input voltage Vin, a control IC 18 has a pin ED
connected to the emitter of a BJT Q1 to switch the BJT Q1 and
thereby convert the input voltage Vin into an output voltage V0, a
current-setting resistor Rset has one terminal connected to the
base of the BJT Q1, and another terminal connected to the base of a
BJT Q2, and thus, by selecting the current-setting resistor Rset,
the base current Ib may be obtained as desired. The control IC 18
has a pin GND connected to a first terminal 20 of the sensing
resistor Rcs and determining a reference potential for the control
IC 18 according to the voltage Vgnd thereon, and has another pin CS
connected to a second terminal 22 of the sensing resistor Rcs, so
that the control IC 18 can determine the inductor current Ic of an
inductor Np according to the voltage drop Vcs-Vgnd in the sensing
resistor Rcs. FIG. 6 shows the control IC 18 shown in FIG. 5, which
includes a switch SW3 connected between pins ED and GND, and a
driver 24 for controlling the switch SW3. When the driver 24 turns
on switch SW3, the current-setting resistor Rset generates the base
current Ib according to the base voltage V2 to turn on the BJT Q1,
as shown at time t1 in FIG. 7. The inductor current Ic at the
collector of the BJT Q1 and the output current Ie of the BJT Q1
accordingly raise. At this time, the current Ie passes through the
sensing resistor Rcs. Since the voltage Vgnd at the first terminal
20 of the sensing resistor Rcs is the reference potential for the
control IC 18, from the perspective of the control IC 18, the
voltage Vcs-Vgnd=-Ie.times.Rcs at the pin CS has a negative value,
as shown by the waveform of Vcs-Vgnd shown in FIG. 7. When the
voltage Vcs-Vgnd reaches the predetermined threshold, the driver 24
turns off the switch SW3 to turn off the BJT Q1, as shown at time
t2 in FIG. 7. However, as stated previously, when the BJT Q1 is
turned off, the BJT Q1 will generate the recovery current Irb that
makes the voltage drop Vcs-Vgnd of the sensing resistor Rcs unable
to represent the inductor current Ic, as happening during the time
period between the time points t2 and t3 in FIG. 7. This hinders
the control IC 18 from getting correct inductor current Ic by
referring to the voltage drop Vcs-Vgnd of the sensing resistor
Rcs.
[0006] Additionally, each of the AC-to-DC power converters shown in
FIG. 1, FIG. 2 and FIG. 5 determines the inductor current Ic
according to the voltage Vcs of the sensing resistor Rcs, and turns
off the BJT Q1 when the inductor current Ic reaches the
predetermined peak Ipeak. However, between the time that the
inductor current Ic reaches time predetermined peak Ipeak and the
time that the. BJT Q1 is turned off, a delay time Td is caused by
the charge stored when the BJT was on, as shown in FIG. 8. The
delay time Td makes the peak of the inductor current Ic goes beyond
the predetermined peak Ipeak. Moreover, the slop of the inductor
current Ic varies with the input voltage Vin. When the input
voltage Vin is low, the slops of the inductor current Ic is
relatively small, and the peak error .DELTA.I1 is relatively small,
as shown by the waveform 26 in FIG. 8. When the input voltage Vin
is high, the slope of the inductor current Ic is relatively large,
and the peak error .DELTA.I2 is relatively large, as shown by the
waveform 28 in FIG. 8.
SUMMARY OF THE INVENTION
[0007] An objective of the present invention is to provide an
AC-to-DC power converter and a control method thereof, wherein the
base current is set from the outside of a control IC.
[0008] Another objective of the present invention is to provide an
AC-to-DC power converter and a control method thereof, wherein the
inductor current can be correctly detected.
[0009] Yet another objective of the present invention is to provide
an AC-to-DC power converter and a control method thereof, wherein
the delay time is compensated.
[0010] A further objective of the present invention is to provide a
control IC of an AC-to-DC power converter.
[0011] According to the present invention, an AC-to-DC power
converter having a BJT as a power switch includes a control IC and
a current-setting resistor connected to a pin of the control IC.
The control IC detects the resistance of the current-setting
resistor to determine the base current of the BJT. The control IC
includes a base-current-setting circuit and a current source. The
base-current-setting circuit detects the resistance of the
current-setting resistor to generate a current-controlling signal.
When the BJT is on, the current source generates the base current
according to the current-controlling signal.
[0012] According to the present invention, an AC-to-DC power
converter having a BJT as a power switch includes a control IC and
a sensing resistor. An output current at the output terminal of the
BJT and the recovery current of the BJT pass through the sensing
resistor. The control IC can correctly determine the inductor
current of an inductor connected to the BJT according to the
voltage drop of the sensing resistor.
[0013] According to the present invention, an AC-to-DC power
converter includes a power switch, an inductor connected to the
power switch, a sensing resistor generating a first voltage at its
first terminal and generating a second voltage at its second
terminal according to the current of the power switch, a shifting
circuit shifting the second voltage to compensate the delay time,
and a control IC determining the inductor current of the inductor
according to a relative voltage between the first voltage and the
shifted second voltage.
[0014] According to the present invention, a control method of an
AC-to-DC power converter having a BJT as a power switch includes
detecting the resistance of a current-setting resistor to generate
a current-controlling signal, and determining a base current to be
provided to a BJT according to the current-controlling signal.
[0015] According to the present invention, a control method of an
AC-to-DC power converter having a BJT as a power switch, includes
when a power switch is on, providing an output current at the
output terminal of the power switch to a sensing resistor to
generate a first voltage and a second voltage at a first terminal
and a second terminal of the sensing resistor, respectively;
shifting the second voltage to compensate a delay time; detecting a
relative voltage between the first voltage and the shifted second
voltage; and when the relative voltage reaches a predetermined
threshold, turning off the power switch.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] These and other objectives, features and advantages of the
present invention will become apparent to those skilled in the art
upon consideration of the following description of the preferred
embodiments according to the present invention taken in conjunction
with the accompanying drawings, in which:
[0017] FIG. 1 is an AC-to-DC power converter using BD
technique;
[0018] FIG. 2 is an AC-to-DC power converter using another BD
technique;
[0019] FIG. 3 is the control IC shown in FIG. 2;
[0020] FIG. 4 shows waveforms of the signals shown in FIG. 2;
[0021] FIG. 5 is an AC-to-DC power converter using ED
technique;
[0022] FIG. 6 shows the control IC shown in FIG. 5;
[0023] FIG. 7 shows waveforms of the signals shown in FIG. 5;
[0024] FIG. 8 shows different inductor currents Ic under different
input voltages;
[0025] FIG. 9 is an AC-to-DC power converter according to the
present invention;
[0026] FIG. 10 shows waveforms of the signals shown in FIG. 9;
[0027] FIG. 11 shows another embodiment for sensing the inductor
current Ic;
[0028] FIG. 12 is a first embodiment of the base-current-setting
circuit shown in FIG. 9;
[0029] FIG. 13 is a second embodiment of the base-current-setting
circuit shown in FIG. 9;
[0030] FIG. 14 is a third embodiment of the base-current-setting
circuit shown in FIG. 9;
[0031] FIG. 15 is a fourth embodiment of the base-current-setting
circuit shown in FIG. 9;
[0032] FIG. 16 is another configuration of the base-current-setting
circuit;
[0033] FIG. 17 is a buck AC-to-DC power converter according to the
present invention;
[0034] FIG. 18 is a boost AC-to-DC power converter according to the
present invention; and
[0035] FIG. 19 is a power converter using a MOSFET as its power
switch.
DETAILED DESCRIPTION OF THE INVENTION
[0036] FIG. 9 shows a fly-back AC-to-DC power converter according
to the present invention, in which a rectifier circuit 10 rectifies
an AC voltage VAC to generate an input voltage Vin, a BJT Q1 works
as a power switch, and a control IC 30 has a pin BD connected to a
base of the BJT Q1 to switch the BJT Q1 in order to convert the
input voltage Vin into an output voltage V0. The BJT Q1 has its
collector working as an input terminal connected to an inductor and
receiving an inductor current Ic and has its emitter working as an
output terminal for providing an output current Ie. A
current-setting resistor Rset is connected to a pin CS of the
control IC 30 to set the base current Ib. The control IC 30 has its
pin GND connected to a first terminal 20 of a sensing resistor Rcs.
The reference potential for the control IC 30 is determined by a
voltage Vgnd at the first terminal 20. The sensing resistor Rcs has
a second terminal 22 connected to the pin CS through the
current-setting resistor Rset. In the control IC 30, the
base-current-setting circuit 32 is connected to the pin CS. During
the duration of setting the base current Ibb, as the period between
the time points T1 and T2 in FIG. 10, the base-current-setting
circuit 32 detects the resistance of the current-setting resistor
Rset to generate and store a current-controlling signal Scc. A
current source 40 provides the base current Ibb according to the
current-controlling signal Scc. A loop controller 42 provides
control signals UC and LC to control the switches SW1 and SW2,
respectively, in order to switch the BJT Q1. A current sensor 44
detects a relative voltage Vcs2-Vgnd between the voltage Vcs2 of
the pin CS and the voltage Vgnd of the pin GND, to determine the
value of the inductor current Ic. The base-current-setting circuit
32 may set the base current Ibb only one time when the AC-to-DC
power converter is activated. Alternatively, it can reset the base
current Ibb once for every switching cycle of the BJT Q1.
Preferably, when the BJT Q1 is turned on, the base-current-setting
circuit 32 immediately adjusts the current-controlling signal Scc
according to the voltage Vcs2 of the pin CS, thereby adjusting the
base current Ibb. The base-current-setting circuit 32 sets the base
current Ibb by using the pin CS that senses the inductor current
Ic, so there are no additional pins needed.
[0037] When the loop controller 42 turns on the switch SW1 and
turns off the switch SW2, the current source 40 provides the base
current Ibb to the base of the BJT Q1 to turn on the BJT Q1. The
inductor current Ic of the secondary side and the output current Ie
of the BJT Q1 raise, as shown at the time point T2 in FIG. 10, and
the current Ircs=Ie+Irb passing through the sensing resistor Rcs
raises with the current Ie. Thus, according to the voltage drop of
the sensing resistor Rcs, the value of the inductor current Ic can
be obtained. A shifting circuit composed of resistors Rcomp and
Rset provides a voltage Vof to shift the voltage Vcs1 at the second
terminal of the sensing resistor Rcs to generate a voltage Vcs2 for
the pin CS. The current sensor 44, according to the relative
voltage Vcs2-Vgnd between the voltage Vcs2 of the pin CS and the
voltage Vgnd of the pin GND, determines the value of the inductor
current Ic. The shifted voltage Vcs2 will make the current sensor
44 send out the current-sensing signal Is to the loop controller 42
to turn off the BJT Q1 before the inductor current Ic reaches the
predetermined peak Ipeak, thereby compensating the peak error
caused by the delay time Td. In the embodiment, the voltage Vcs2 is
smaller than the voltage Vgnd, so the relative voltage
Vcs2-Vgnd=-Ircs.times.Rcs is a negative voltage. The resistors
Rcomp and Rset divide the voltage Vaux of the auxiliary coil Na, to
generate a voltage drop Vof=[Rset/(Rset+Rcomp)].times.Vaux on the
resistor Rset. By appropriately selecting the ratio between the
resistors Rcomp and Rset to adjust the voltage Vof, it is possible
to make the peak of the inductor current Ic equal to the
predetermined peak Ipeak. Additionally, when the BJT Q1 is on, the
voltage Vaux of the auxiliary coil Na varies with the input voltage
Vin, so the voltage Vof varies with the input voltage Vin, thereby
compensating the peak error as the input voltage Vin varies.
[0038] When the loop controller 42 turns off the switch SW1 and
turns on the switch SW2 to turn off the BJT Q1, as shown at time T3
in FIG. 10, the BJT Q1 generates a recovery current Irb that flows
from the collector of the BJT Q1 to the sensing resistor Rcs
through the base of the BJT Q1 and the switch SW2. Therefore, the
current Ircs of the sensing resistor Rcs remains going up with the
inductor current Ic. As shown in the period between the time points
T2 and T4 in FIG. 10, the waveforms of the current. Ircs and of the
inductor current Ic are coincident. The control IC 30 is thus
enabled to correctly sense the inductor current Ic according to the
voltage drop of the sensing resistor Rcs. In other words, the
current sensor 44 is enabled to correctly sense the inductor
current Ic according to the relative voltage Vcs2-Vgnd.
[0039] FIG. 11 is another embodiment for sensing the inductor
current Ic, in which a control IC 30 has a pin CS connected to a
first terminal 20 of the sensing resistor Rcs, and has a pin GND
connected to a second terminal 22 of the sensing resistor Rcs, the
switch SW2 is connected between pins BD and CS of the control IC
30, and the voltage Vgnd of the pin GND is the reference potential
for the control IC. When the switch SW1 is turned on and the switch
SW2 is turned off to make the BJT Q1 on, the output current Ie
passes through the sensing resistor Rcs. When the switch SW1 is
turned off and the switch SW2 is turned on to make the BJT Q1 off,
the recovery current Irb flows from the collector of the BJT Q1
through the base of the BJT Q1 and the switch SW2 to the sensing
resistor Rcs. Thus, the current sensor 44 is enabled to correctly
sense the inductor current Ic according to the relative voltage
Vcs2-Vgnd between the voltage Vcs2 and the voltage Vgnd. In the
embodiment, the voltage Vcs2 is greater than the voltage Vgnd, so
the relative voltage Vcs2-Vgnd=Ircs.times.Rcs is a positive
voltage.
[0040] In the embodiment shown in FIG. 9, the base-current-setting
circuit 32 includes a detector 34, a storage unit 36 and a
translate circuit 38. The detector 34 detects the resistance of the
current-setting resistor Rset when the AC-to-DC power converter is
activated or when the BJT Q1 is off, to generate a detecting signal
Sd. The storage unit 36 stores the detecting signal Sd when the
AC-to-DC power converter is activated or when the BJT Q1 is off.
The translate circuit 38 generates the current-controlling signal
Scc for controlling the base current Ibb according to the detecting
signal Sd stored in the storage unit 36. Preferably, when the BJT
Q1 is on, the translate circuit 38 can immediately adjust the
current-controlling signal Scc according to the voltage Vcs2 of the
pin CS, to in turn adjust the base current Ibb.
[0041] FIG. 12 shows a first embodiment of the base-current-setting
circuit 32 shown in FIG. 9, in which an analogy-to-digital
converter (ADC) is used as the detector 34 for detecting the
resistance of the current-setting resistor Rset and converting the
resistance into a digital detecting signal Sd, a memory is used as
the storage unit 36 for storing the digital detecting signal Sd,
and a digital-to-analogy (DAC) is used as the translate circuit 38
for converting the detecting signal Sd stored in the storage unit
36 into an analog current-controlling signal Scc. Preferably, when
the BJT Q1 is on, the translate circuit 38 can immediately adjust
the current-controlling signal Scc according to the voltage Vcs2 of
the pin CS.
[0042] FIG. 13 shows a second embodiment of the
base-current-setting circuit 32 of FIG. 9. Similar to the
embodiment of FIG. 12, the detector 34 and the storage unit 36 are
realized by an ADC and a memory, respectively. However, in the
embodiment of FIG. 13, the translate circuit 38 is realized by a
mapping table. The translate circuit 38 selects the corresponding
current-controlling signal Scc by checking the mapping table
according to the detecting signal Sd stored in the memory.
Preferably, when the BJT Q1 is on, the translate circuit 38 can
immediately adjust the current-controlling signal Scc according to
the voltage Vcs2 of the pin CS.
[0043] FIG. 14 shows a third embodiment of the base-current-setting
circuit 32 shown in FIG. 9, in which the detector 34 includes a
current source 46 and an ADC 48. The current source 46 provides a
current Id to the current-setting resistor Rset to generate a
voltage Vset for determination of the resistance of the
current-setting resistor Rset. The ADC 48 converts the voltage Vset
into a digital detecting signal Sd. The memory working as the
storage unit 36 stores the detecting signal Sd. The translate
circuit 38 includes a current source 50 that provides the
current-controlling signal Scc according to the detecting signal
Sd. The current source 40 includes a current mirror composed of
transistors M1 and M2 for mirroring the current-controlling signal
Scc to generate the base current Ibb. Preferably, when the BJT Q1
is on, the current source 50 can immediately adjust the
current-controlling signal Scc according to the voltage Vcs2 of the
pin CS.
[0044] FIG. 15 shows a fourth embodiment of the
base-current-setting circuit 32 shown in FIG. 9, in which the
detector 34 includes an operational amplifier 52 and transistors M3
and M4. The operational amplifier 52 applies a voltage Vref to the
current-setting resistor Rset to generate a current Im1 for
determination of the resistance of the current-setting resistor
Rset. The current Im1 passes through the transistors M3 and M4 and
determines the detecting signal Sd on the gate of the transistor
M4. The embodiment of FIG. 15 uses a sample and hold circuit as the
storage unit 36 for storing the detecting signal Sd. In FIG. 15,
the translate circuit 38 includes transistors M5, M6 and M7. The
storage unit 36 provides the detecting signal Sd to the gate of the
transistor M5. Since the transistors M4 and M5 have the same gate
voltage, they form a current mirror to mirror the current Im1 to
generate a current Im2. The transistors M6 and M7 of the translate
circuit 38 also form a current mirror to mirror the current Im2 to
generate the current-controlling signal Scc. The current source 40
includes a current mirror composed of transistors M1 and M2 to
mirror the current-controlling signal Scc, thereby generating the
base current Ibb.
[0045] In the embodiments of FIG. 12 through FIG. 15, the detector
34 and the storage unit 36 may detect the current-setting resistor
Rset and store the detecting signal Sd according to the
power-on-resetting signal POR when the AC-to-DC power converter is
activated. Alternatively, they may detect the current-setting
resistor Rset and store the detecting signal Sd according to the
control signal UC or LC when every time the BJT Q1 is off.
[0046] FIG. 16 provides another configuration of the
base-current-setting circuit 32, which includes a detector 34 and a
storage unit 36. The detector 34 detects the resistance of the
current-setting resistor Rset to generate the current-controlling
signal Scc. The storage unit 36 stores the current-controlling
signal Scc and provides the current-controlling signal Scc to the
current source 40 to control the base current Ibb. The detector 34
is as shown in FIG. 12 through FIG. 15. The storage unit 36 may be
a memory or a sample and hold circuit. In FIG. 16, the detector 34
and the storage unit 36 may detect the current-setting resistor
Rset and store the current-controlling signal Scc according to the
power-on-resetting signal POR when the AC-to-DC power converter is
activated. Alternatively, they may detect the current-setting
resistor Rset and store the current-controlling signal Scc
according to the control signal UC or LC when every time the BJT Q1
is off.
[0047] In addition to the fly-back AC-to-DC power converter as
shown in FIG. 9, the present invention is also applicable to a buck
or boost AC-to-DC power converter. FIG. 17 shows a buck AC-to-DC
power converter according to the present invention, in which a
rectifier circuit 10 rectifies an AC voltage VAC to generate an
input voltage Vin, and a control IC 30 has a pin BD connected to
the base of the BJT Q1 for switching the BJT Q1 to converter the
input voltage Vin into an output voltage V0. The control IC 30
operates as the circuit of FIG. 9 does. The base-current-setting
circuit 32 generates the current-controlling signal Scc for the
current source 40 by detecting the resistance of the
current-setting resistor Rset, to in turn determine the base
current Ibb. When the switch SW1 is turned on and the switch SW2 is
turned off, the current Ibb is provided to the base of the BJT Q1,
to turn on the BJT Q1. When the BJT Q1 is on, the current Ircs=Ie
passes through the sensing resistor Rcs. The control IC 30 takes
the voltage Vgnd at the first terminal 20 of the sensing resistor
Rcs as the reference potential. The auxiliary coil Na senses the
voltage of the inductor L1 to generate a voltage Vaux. Resistors
Rcomp and Rset divide the voltage Vaux to generate a voltage drop
Vof on the resistor Rset for compensating the delay time Td. The
voltage drop Vof of the resistor Rset shifts the voltage Vcs1 at
the second terminal 22 of the resistor Rcs to generate a voltage
Vcs2 for pin CS. In the control IC 30, the current sensor 44
generates the current-sensing signal Is according to the relative
voltage Vcs2-Vgnd between the voltage Vcs2 and the voltage Vgnd.
Since the voltage of the inductor L1 varies with the input voltage
Vin, the voltage drop Vof of the resistor Rset also varies with the
input voltage Vin, thereby allowing the inductor current IL to have
the same peak even if the input voltage Vin varies. When the switch
SW1 is turned off and the switch SW2 is turned on, the BJT Q1 is
turned off. At the same time the BJT Q1 generates a recovery
current Irb that flows from the collector to the sensing resistor
Rcs through the base and the switch SW2. Thus, the waveform of the
current Ircs of the sensing resistor Rcs concerts with the going-up
waveform of the inductor current IL. The control IC 30 thus can
obtain the going-up waveform of the inductor current IL by
referring to the voltage drop of the sensing resistor Rcs.
[0048] FIG. 18 shows a boost AC-to-DC power converter according to
the present invention, in which a rectifier circuit 10 rectifies an
AC voltage VAC to generate an input voltage Vin, and a control IC
30 has a pin BD connected to the base of a BJT Q1 for switching the
BJT Q1 to convert the input voltage Vin into an output voltage V0.
The control IC 30 operates as the circuit of FIG. 9 does, in which
the base-current-setting circuit 32 generates the
current-controlling signal Scc for the current source 40 by
detecting the resistance of the current-setting resistor Rset, in
turn determining the base current Ibb. When the switch SW1 is
turned on and the switch SW2 is turned off, the base current Ibb is
provided to the base of the BJT Q1 to turn on the BJT Q1. When the
BJT Q1 is on, the current Ircs=Ie passes through the sensing
resistor Rcs. The control IC 30 takes the voltage Vgnd at the first
terminal 20 of the sensing resistor Rcs as the reference potential.
The auxiliary coil Na senses the voltage of the inductor L1 to
generate a voltage Vaux. Resistors Rcomp and Rset divide the
voltage Vaux to generate a voltage drop Vof on the resistor Rset
for compensating the delay time Td. The voltage drop Vof of the
resistor Rset shifts the voltage Vcs1 at the second terminal 22 of
the resistor Rcs to generate a voltage Vcs2 for the pin CS. In the
control IC 30, the current sensor 44 generates the current-sensing
signal Is according to the relative voltage Vcs2-Vgnd between the
voltage Vcs2 and the voltage Vgnd. Since the voltage of the
inductor L1 varies with the input voltage Vin, the voltage drop Vof
of the resistor Rset also varies with the input voltage Vin,
thereby allowing the inductor current IL to have the same peak even
if the input voltage Vin varies. When the switch SW1 is turned off
and the switch SW2 is turned on to turn off the BJT Q1, the BJT Q1
generates a recovery current Irb that flows from the collector to
the sensing resistor Rcs through the base and the switch SW2. Thus,
the waveform of the current Ircs of the sensing resistor Rcs
concerts with the going-up waveform of the inductor current IL. The
control IC 30 thus can obtain the going-up waveform of the inductor
current IL by referring to the voltage drop of the sensing resistor
Rcs.
[0049] In the above embodiments, while description is made to the
AC-to-DC power converter using BD technique, it is noted that the
use of the present invention is not limited to AC-to-DC power
converters using BD technique. People skilled in the art would be
enabled by the disclosure herein to easily apply the present
invention to any AC-to-DC power converter using ED technique. In
addition, while the base-current-setting circuit 32 sets the base
current Ibb by using the pin CS that senses the inductor current Ic
in the above embodiments, the base-current-setting circuit 32 may
use a pin having a different function or use an additional
unoccupied pin to set the base current Ibb in other
embodiments.
[0050] In a power converter using a MOSFET as its power switch, the
delay time Td can also happen. The method of delay-time
compensation disclosed in the present invention is also applicable
to this kind of power converters. FIG. 19 shows a power converter
using a MOSFET as its power switch, in which a loop controller 64
is connected to the gate of the MOSFET Mp through the pin GD of the
control IC 60 to switch the MOSFET Mp, a sensing resistor Rcs has
its first terminal 20 connected to the pin GND of the control IC 60
and the output terminal of the MOSFET Mp, and serially-connected
resistors Rcomp and Rset are connected to the second terminal 22 of
the sensing resistor Rcs, to divide the voltage Vaux and generate a
voltage drop Vof on the resistor Rset. The voltage drop Vof of the
resistor Rset shifts the voltage Vcs1 at the second terminal 22 of
the resistor Rset to generate a voltage Vcs2 for the pin CS of the
control IC 60. The current sensor 62 triggers the current-sensing
signal Is at an earlier time point according to the shifted voltage
Vcs2, to compensate the delay time Td. Preferably, the voltage Vaux
may vary with the input voltage Vin to prevent the peak of the
current Imp of the MOSFET Mp from varying with the input voltage
Vin.
[0051] While the present invention has been described in
conjunction with preferred embodiments thereof, it is evident that
many alternatives, modifications and variations will be apparent to
those skilled in the art. Accordingly, it is intended to embrace
all such alternatives, modifications and variations that fall
within the spirit and scope thereof as set forth in the appended
claims.
* * * * *