TW201511450A - Control circuits and synchronous rectifying control circuits - Google Patents

Abstract

A synchronous rectifying control circuit of a power converter is provided. The synchronous rectifying control circuit comprises a synchronous rectifying driver, a charge pump capacitor, and a capacitor. The synchronous rectifying driver is coupled to a transformer for generating a control signal to switch a transistor. The charge pump capacitor is coupled to a power source for generating a charge pump voltage. The capacitor is coupled to store the charge pump voltage. The transistor is coupled to the transformer and operated as a synchronous rectifier. The charge pump voltage is coupled to guarantee a sufficient driving capability for the control signal.

Description

Control circuit and synchronous rectification control circuit

The present invention relates to a synchronous rectification control circuit, and more particularly to a control circuit having a synchronous rectification of a charge pump to improve the efficiency of the power converter.

Synchronous rectification techniques have been disclosed in many conventional techniques, for example, U.S. Patent No. 6,995,991 entitled "Synchronous Rectification Circuit for Power Converters" under the designation "PWM Controller for Synchronous Rectifier of Flyback Power Converter" and numbered 7,440,298 U.S. Patent, and U.S. Patent No. 8,072,787, entitled "Synchronous Rectifying for Soft Switching Power Converters".

Figure 1 shows a conventional power converter with synchronous rectification. The transistor 20 controlled by the switching signal S _W is coupled to switch the transformer 10 to transfer energy from the input voltage V _IN to the output voltage V _{O of the} power converter. When the rectifier 35 (or the body diode of the transistor 30) is turned on to transfer power from the transformer 10 to the output capacitor 40, the transistor 30 will conduct to reduce the conduction loss of the rectifier 35 (the forward bias of the rectifier 35) ). The terminal DET of the synchronous rectification control circuit 50 is coupled to the transistor 30 and/or the transformer 10 to detect the signal S _DET and achieve synchronous rectification. The synchronous rectification control circuit 50 generates a control signal V _G at its end point VG based on the signal S _DET . The control signal V _G is used to switch the transistor 30. In most applications, the power supply (V _CC ) at the terminal VCC of the synchronous rectification control circuit 50 is supplied by the output voltage V _{O of} the power converter. A disadvantage of these applications is that when the output voltage V _O becomes a low voltage, the voltage level of the control signal V _G is insufficient to drive the transistor 30.

Figure 2 is a graph showing the voltage-current curve of a conventional power converter (output voltage V _O versus output current I _O ). When the power converter is operating in constant current mode, the output voltage V _O will be a low voltage. In region 65, the output voltage V _{O is} relatively low. In the event that the power converter operates in region 65, the power supply (V _CC ) of the synchronous rectification control circuit 50 will be too low to allow the control signal _VG to fully conduct the transistor 30. This will cause inefficiencies in the power converter.

The present invention provides a synchronous rectification control circuit having a charge pump and for a power converter. The synchronous current control circuit includes: a synchronous rectification driver, a charge pump capacitor, a capacitor, a plurality of switches, an oscillator, and a detection circuit. The synchronous rectification driver is coupled to the transformer and generates a control signal to switch the transistor. The charge pump capacitor is coupled to the power supply and generates a charge pump voltage. The capacitor stores the charge pump voltage. The transistor is coupled to the transformer and operates like a synchronous rectifier. The charge pump voltage ensures sufficient drive capability of the control signal. The plurality of switches charge the charge pump capacitor in a switching manner, thereby implementing a charge pump. The oscillator generates an oscillating signal to effect the switching of the charge pump capacitor. The detection circuit detects the voltage level of the power supply. When the voltage level of the power supply is higher than the threshold, the detection circuit generates a detection signal. The detection signal disables the charge pump and transfers the power to the capacitor. When the charge pump voltage is below the low voltage threshold, the control signal is disabled. When the charge pump voltage is above the high voltage threshold, the control signal is enabled.

The present invention provides a control circuit for synchronous rectification of a power converter. The control circuit includes a synchronous rectification driver, a boost inductor, a capacitor, a switch, a detection circuit, and an oscillator. The synchronous rectification driver is coupled to the transformer and generates a control signal to switch the transistor. The boost inductor is coupled to the power supply and generates a boost voltage. The capacitor stores the boost voltage. The transistor is coupled to the transformer and operates like a synchronous rectifier. The boost voltage ensures sufficient drive capability of the control signal. The switch is used to switch the boost inductor to implement the boost switching operation. The detection circuit detects the voltage level of the power supply. When the voltage level of the power supply is higher than the threshold, the detection circuit generates a detection signal. The detection signal disables the boost switching operation and delivers power to the capacitor. The oscillator generates an oscillating signal to switch the boost inductor. When the boost voltage is below the low voltage threshold, the control signal is disabled. When the boost voltage is above the high voltage threshold, the control signal is enabled.

figure 1:

10‧‧‧Transformers

20‧‧‧Optoelectronics

30‧‧‧Optoelectronics

35‧‧‧Rectifier

40‧‧‧ output capacitor

50‧‧‧Synchronous rectification control circuit

DET‧‧‧ endpoint

GND‧‧‧Endpoint

I _O ‧‧‧Output current

S _DET ‧‧‧Detection signal

S _W ‧‧‧Switching signal

V _CC ‧‧‧Voltage (power supply)

V _G ‧‧‧ control signal

V _IN ‧‧‧ input voltage

V _O ‧‧‧Output voltage

VCC‧‧‧ endpoint

VG‧‧‧ endpoint

figure 2:

65‧‧‧Area

I _O ‧‧‧Output current

V _O ‧‧‧Output voltage

image 3:

10‧‧‧Transformers

20‧‧‧Optoelectronics

30‧‧‧Optoelectronics

35‧‧‧Rectifier

40‧‧‧ output capacitor

51‧‧‧Charge pump capacitor

52‧‧‧ capacitor

100‧‧‧Synchronous rectification control circuit

DET‧‧‧ endpoint

GND‧‧‧Endpoint

I _O ‧‧‧Output current

S _DET ‧‧‧Detection signal

S _W ‧‧‧Switching signal

V _CC ‧‧‧Voltage (power supply)

V _G ‧‧‧ control signal

V _IN ‧‧‧ input voltage

V _O ‧‧‧Output voltage

VCC‧‧‧ endpoint

VDD‧‧‧ endpoint

VG‧‧‧ endpoint

X, Y‧‧‧ endpoint

Figure 4:

51‧‧‧Charge pump capacitor

52‧‧‧ capacitor

71, 72, 73, 74‧‧ ‧ switch

100‧‧‧Synchronous rectification control circuit

200‧‧‧Timer Circuit

300‧‧‧Synchronous rectification driver

S ₁ , S ₂ , S ₃ , S ₄ ‧ ‧ signals

S _DET ‧‧‧Detection signal

V _CC ‧‧‧Voltage (power supply)

V _DD ‧‧‧ voltage (charge pump voltage)

V _G ‧‧‧ control signal

VCC‧‧‧ endpoint

VDD‧‧‧ endpoint

X, Y‧‧‧ endpoint

Figure 5:

200‧‧‧Timer Circuit

210‧‧‧Oscillator

215‧‧‧ comparator

230‧‧‧Fracture

250‧‧‧Signal Generator

251, 252, 254‧‧‧ or gate

253‧‧‧Anti-gate

S ₁ , S ₂ , S ₃ , S ₄ ‧ ‧ signals

S _A , S _B , S _C , S _D ‧‧‧ signals

S _OSC ‧‧‧Oscillation signal

S _V ‧‧‧Detection signal

V _CC ‧‧‧Voltage (power supply)

Figures 6A, 6B, 7:

51‧‧‧Charge pump capacitor

52‧‧‧ capacitor

71, 72, 73, 74‧‧ ‧ switch

S ₁ , S ₂ , S ₃ , S ₄ ‧ ‧ signals

VCC‧‧‧ endpoint

VDD‧‧‧ endpoint

X, Y‧‧‧ endpoint

Figure 8:

300‧‧‧Synchronous rectification driver

310‧‧‧ Comparator

315‧‧‧Inverter

320, 321‧‧ ‧ switch

350‧‧‧Synchronous rectified signal generator

S _DET ‧‧‧Detection signal

S _UV ‧‧‧ signal

V _CC ‧‧‧Voltage (power supply)

V _DD ‧‧‧ voltage (charge pump voltage)

V _G ‧‧‧ control signal

V _T2 ‧‧‧High voltage threshold

V _T3 ‧‧‧ low voltage threshold

Figure 9:

10‧‧‧Transformers

20‧‧‧Optoelectronics

30‧‧‧Optoelectronics

35‧‧‧Rectifier

40‧‧‧ output capacitor

52‧‧‧ capacitor

53‧‧‧Boost Inductors

500‧‧‧Synchronous rectification control circuit

B‧‧‧Endpoint

DET‧‧‧ endpoint

GND‧‧‧Endpoint

I _O ‧‧‧Output current

S _DET ‧‧‧Detection signal

S _W ‧‧‧Switching signal

V _CC ‧‧‧Voltage (power supply)

V _G ‧‧‧ control signal

V _IN ‧‧‧ input voltage

V _O ‧‧‧Output voltage

VCC‧‧‧ endpoint

VDD‧‧‧ endpoint

VG‧‧‧ endpoint

Figure 10:

52‧‧‧ capacitor

53‧‧‧Boost Inductors

210‧‧‧Oscillator

215‧‧‧ comparator

230‧‧‧Fracture

300‧‧‧Synchronous rectification driver

500‧‧‧Synchronous rectification control circuit

510, 520‧‧ ‧ switch

515‧‧‧Anti-gate

525‧‧‧ or gate

600‧‧‧Signal Generator

B‧‧‧Endpoint

S _DET ‧‧‧Detection signal

S _OSC ‧‧‧Oscillation signal

S _V ‧‧‧Detection signal

S _X , S _Y ‧‧‧ signals

V _CC ‧‧‧Voltage (power supply)

V _DD ‧‧‧ voltage (charge pump voltage)

V _G ‧‧‧ control signal

VCC‧‧‧ endpoint

VDD‧‧‧ endpoint

Figures 11A, 11B, 12:

52‧‧‧ capacitor

53‧‧‧Boost Inductors

510, 520‧‧ ‧ switch

B‧‧‧Endpoint

I _L ‧‧‧current

S _X , S _Y ‧‧‧ signals

V _CC ‧‧‧Voltage (power supply)

VCC‧‧‧ endpoint

VDD‧‧‧ endpoint

Figure 1 shows a conventional power converter with synchronous rectification.

Figure 2 shows the voltage-current curve of the power converter with synchronous rectification in Figure 1.

3 shows a power converter with synchronous rectification in accordance with an embodiment of the present invention.

4 shows a synchronous rectification control circuit of the power converter of FIG. 3, in accordance with an embodiment of the present invention.

Figure 5 shows a sequencer circuit of the synchronous rectification control circuit of Figure 4, in accordance with an embodiment of the present invention.

6A and 6B respectively show the charge pump of the synchronous rectification controller of FIG. The first cycle and the second cycle.

Figure 7 is a diagram showing the operation of the synchronous rectification controller having no charge pump in Figure 3; Figure 8 shows a synchronous rectification driver of the synchronous rectification control circuit of Figure 4, in accordance with an embodiment of the present invention.

Figure 9 shows a power converter with synchronous rectification in accordance with another embodiment of the present invention.

Figure 10 shows a synchronous rectification control circuit of the power converter of Figure 9 in accordance with an embodiment of the present invention.

11A and 11B show the first cycle and the second cycle of the boost switching operation of the synchronous rectification controller of Fig. 9, respectively.

Fig. 12 shows the operation of the synchronous rectification controller in Fig. 9 without the boost switching operation.

The above described objects, features and advantages of the present invention will become more apparent from the description of the appended claims.

3 is a diagram showing a power converter in accordance with an embodiment of the present invention. The transistor 20 controlled by the switching signal S _W is coupled to switch the transformer 10 to transfer energy from the input voltage V _IN to the output voltage V _{O of the} power converter. When the rectifier 35 (or the body diode of the transistor 30) is turned on to transfer power from the transformer 10 to the output capacitor 40, the transistor 30 will conduct to reduce the conduction loss of the rectifier 35 (the forward bias of the rectifier 35) ). The operation of the transistor 30 is such that it is the same synchronous rectifier. The terminal DET of the synchronous rectification control circuit 50 is coupled to the transistor 30 and/or the transformer 10 to detect the signal S _DET and achieve synchronous rectification. A charge pump synchronous rectification control circuit 100 is operative to drive the transistor 30. The synchronous rectification controller 100 is coupled to the charge pump capacitor 51 between its terminals X and Y to boost and store the V _CC voltage (power supply) to the capacitor 52, thus at the terminal VDD of the synchronous rectification control circuit 100. A V _DD voltage is generated. The level of the V _DD voltage is higher than the level of the V _CC voltage. The V _DD voltage ensures that the control signal V _G generated at the terminal VG of the synchronous rectification control circuit 100 has sufficient driving capability to drive the transistor 30. When the V _CC voltage is a high voltage, the synchronous rectification control circuit 100 disables the charge pump and directly couples the V _CC voltage into a V _DD voltage.

4 is a diagram showing a synchronous rectification control circuit 100 in accordance with an embodiment of the present invention. The synchronous rectification control circuit 100 includes a plurality of switches 71, 72, 73, and 74, a sequencer circuit 200, and a synchronous rectification driver 300. The synchronous rectification driver 300 is coupled to the transformer 10 to generate a control signal V _G to switch the transistor 30. These switches 71, 72, 73, and 74 are coupled to a charge pump capacitor 51 to generate a V _DD voltage. The on/off states of the switches 71, 72, 73, and 74 are controlled by the signals S ₁ , S ₂ , S ₃ , and S ₄ generated by the sequencer circuit 200, respectively. The V _CC voltage (power supply) at the terminal VCC of the synchronous rectification control circuit 100 is coupled to the sequencer circuit 200 to generate signals S ₁ , S ₂ , S ₃ , and S ₄ . The V _DD voltage is coupled to supply power to the synchronous rectification driver 300. The synchronous rectification driver 300 generates a control signal V _G based on the V _CC voltage and/or the signal S _DET . The operation of detecting the signal S _DET to generate the control signal V _G to drive the transistor 30 is known to those of ordinary skill in the art, and thus the related description is omitted herein.

FIG. 5 shows a sequencer circuit 200 of a synchronous rectification control circuit 100 in accordance with an embodiment of the present invention. The sequencer circuit 200 includes an oscillator 210, a comparator 215, a flip-flop 230, a signal generator 250, or gates 251, 252 and 254, and an inverse gate 253. Oscillator 210 produces an oscillating signal S _OSC that is coupled to signal generator 250 to produce signals S _A , S _B , S _C , and S _D . The comparator 215 and the flip-flop 230 form a detection circuit for detecting V _CC (power). The comparator 215 receives the V _CC voltage (power supply) and the threshold V _T1 and compares the two. When the V _CC voltage is higher than the threshold value V _T1 , the comparator 215 generates the detection signal S _V through the flip-flop 230. The detection signal S _V and the signals S _A , S _B , S _D , and the S _C transmission or gates 251 , 252 and 254 and the inverse gate 253 generate signals S ₁ , S ₂ , S ₄ , and S _{3 , respectively} . In the first period (FIG. 6A), the signal S ₁ and S ₂ is enabled to turn on the switch 71 and, respectively 72. The voltage across the charge pump capacitor 51 will be charged to the same level as the level of the V _CC voltage. In the second period (FIG. 6B), the signal S ₃ and S _4, respectively, is enabled to turn on the switch 73 and 74. The V _CC voltage and the voltage across the charge pump capacitor 51 will be summed to charge the capacitor 52. That is, the summed voltage of the V _CC voltage and the voltage across the charge pump capacitor 51 will be stored in the capacitor 52. At this time, the level of the V _DD voltage will be approximately equal to twice the level of the V _CC voltage. When the V _CC voltage is higher than the threshold value V _T1 , the detection signal S _V will be generated to disable the signal S ₃ and the enable signals S ₁ , S ₂ , and S ₄ (shown in FIG. 7 , the switches 71 , 72 , It is turned on with 74 and switch 73 is turned off), therefore, the V _CC voltage will be directly supplied as the V _DD voltage (the charge pump will be disabled).

FIG. 8 shows a synchronous rectification driver 300 in accordance with an embodiment of the present invention. The synchronous rectification driver 300 includes a comparator 310, an inverter 315, switches 320 and 321 and a synchronous rectification signal generator 350. The V _DD voltage is coupled to power the synchronous rectified signal generator 350. The synchronous rectification signal generator 350 generates a control signal V _G based on the signal S _UV and the V _CC voltage and/or the signal S _DET . When the V _DD voltage is above a high voltage threshold V _T2 , the signal S _UV is generated (enabled) by the comparator 310. When the signal S _UV is enabled, the control signal _VG is enabled. Inverter 315 and switches 320 and 321 form a hysteresis circuit. When the V _DD voltage is below a low voltage threshold V _T3 , the signal S _{UV is} disabled. Wherein, the level of the high voltage threshold V _T2 is higher than the level of the low voltage threshold V _T3 . When the signal S _{UV is} disabled, the control signal V _{G is} disabled.

Figure 9 is a diagram showing a power converter with synchronous rectification in accordance with another embodiment of the present invention. A synchronous rectification control circuit 500 having a charge pump is coupled to drive the transistor 30. The synchronous rectification control circuit 500 is coupled to the boost inductor 53 to boost the V _CC voltage (power supply) to the V _DD voltage, thereby being stored in the capacitor 52, wherein the boost inductor 53 is coupled to the synchronous rectification control circuit 500. Endpoint B. The V _DD voltage ensures that the control signal V _G generated at the terminal VG of the synchronous rectification control circuit 500 has sufficient driving capability to drive the transistor 30. When the V _CC voltage is a high voltage, the synchronous rectification control circuit 500 disables the boost switching operation and directly couples the V _CC voltage into the V _DD voltage.

FIG. 10 shows a synchronous rectification control circuit 500 in accordance with an embodiment of the present invention. The synchronous rectification control circuit 500 includes an oscillator 210, a comparator 215, a flip-flop 230, a synchronous rectification driver 300, switches 510 and 520, an inverse OR gate 515, or a gate 525, and a signal generator 600. Switches 510 and 520 are coupled to switch boost inductor 53 to generate a V _DD voltage. The on/off states of switches 510 and 520 are controlled by signals S _X and S _Y , respectively. Oscillator 210 produces an oscillating signal S _OSC that is coupled to signal generator 600. Based on the level of the V _DD voltage, the signal generator 600 transmits the signals S _X and S _Y through the inverse OR gate 515 and the OR gate 525, respectively. When the V _CC voltage is higher than the threshold value V _T1 , the comparator 215 transmits the detection signal S _V through the flip-flop 230. According to the detection signal S _V , the signals S _X and S _Y are respectively generated by the inverse gate 515 and the OR gate 525. The V _DD voltage is coupled to power the synchronous rectification driver 300. The synchronous rectification driver 300 generates a control signal V _G based on the V _CC voltage and/or the signal S _DET .

11A and 11B respectively show the first cycle and the second cycle of the boost switching operation of the charge pump of the synchronous rectification control circuit 500. Referring to FIG. 11A, when the signal S _X is enabled and the switch 510 is turned on, the boost inductor 53 is charged by the current I _L . At this time, the energy stored in the boost inductor 53 generates a boosted voltage. Referring to FIG. 11B, when signal S _Y is enabled and switch 520 is turned on, the energy of boost inductor 53 is discharged to charge capacitor 52, thereby generating a V _DD voltage. Therefore, the boost voltage will be stored in the capacitor 52. Refer to the following formula: Where T _ON is the on-time of the switch 510 (the enable time of the signal S _X ). T is the switching period of the signal S _X . L ₅₃ is the inductance value of the boost inductor 53.

Fig. 12 shows a charge pump of the synchronous rectification control circuit 500 that does not have a boost switching operation. When the V _CC voltage is higher than the threshold value V _T1 , the detection signal S _V will generate the disable signal S _X and the enable signal S _Y . As a result, the switch 520 is turned on. Therefore, the V _CC voltage will be supplied as the V _DD voltage (without boost switching operation).

The present invention has been disclosed in the above preferred embodiments, and is not intended to limit the scope of the present invention. Any one of ordinary skill in the art can make a few changes without departing from the spirit and scope of the invention. The scope of protection of the present invention is therefore defined by the scope of the appended claims.

10‧‧‧Transformers

20‧‧‧Optoelectronics

30‧‧‧Optoelectronics

35‧‧‧Rectifier

40‧‧‧ output capacitor

51‧‧‧Charge pump capacitor

52‧‧‧ capacitor

100‧‧‧Synchronous rectification control circuit

DET‧‧‧ endpoint

GND‧‧‧Endpoint

I _O ‧‧‧Output current

S _DET ‧‧‧Detection signal

S _W ‧‧‧Switching signal

V _CC ‧‧‧Voltage (power supply)

V _G ‧‧‧ control signal

V _IN ‧‧‧ input voltage

V _O ‧‧‧Output voltage

VCC‧‧‧ endpoint

VDD‧‧‧ endpoint

VG‧‧‧ endpoint

X, Y‧‧‧ endpoint

Claims (12)

A synchronous rectification control circuit having a charge pump and used in a power converter includes: a synchronous rectification driver coupled to a transformer and generating a control signal for switching a transistor; a charge pump capacitor coupled to a power supply, And generating a charge pump voltage; and a capacitor storing the charge pump voltage; wherein the transistor is coupled to the transformer and operating as a synchronous rectifier; and wherein the charge pump voltage ensures a sufficient drive of the control signal ability. The synchronous rectification control circuit of claim 1, further comprising: a plurality of switches for charging the charge pump capacitor in a switching manner, thereby implementing a charge pump. The synchronous rectification control circuit of claim 1, further comprising: an oscillator that generates an oscillating signal to implement the switching mode of the charge pump capacitor. For example, the synchronous rectification control circuit described in claim 1 of the patent scope further includes: a detecting circuit for detecting a voltage level of the power source; wherein, when the voltage level of the power source is higher than a threshold, the detecting circuit generates a detecting signal; and wherein the detecting signal is forbidden The charge pump can be delivered and the power source can be delivered to the capacitor. The synchronous rectification control circuit of claim 1, wherein the control signal is disabled when the charge pump voltage is lower than a low voltage threshold. The synchronous rectification control circuit of claim 1, wherein the control signal is enabled when the charge pump voltage is higher than a high voltage threshold. A control circuit for synchronous rectification of a power converter includes: a synchronous rectification driver coupled to a transformer and generating a control signal for switching a transistor; a boost inductor coupled to a power supply and generating a a boost voltage; and a capacitor storing the boost voltage; wherein the transistor is coupled to the transformer and operates as a synchronous rectifier; and wherein the boost voltage ensures a sufficient drive capability of the control signal. The control circuit of claim 7, further comprising: a switch that switches the boost inductor to implement a boost switching operation. For example, the control circuit described in claim 8 of the patent scope further includes: a detecting circuit for detecting a voltage level of the power source; wherein, when the voltage level of the power source is higher than a threshold, the detecting circuit generates a detecting signal; and wherein the detecting signal is forbidden The boost switching operation can be performed and the power source can be delivered to the capacitor. The control circuit of claim 7, further comprising: an oscillator that generates an oscillating signal to switch the boost inductor. The control circuit of claim 7, wherein the control signal is disabled when the boosted voltage is lower than a low voltage threshold. The control circuit of claim 7, wherein the control signal is enabled when the boost voltage is above a high voltage threshold.