A synchronous rectification control circuit based on driving voltage pre-modulation technique

Abstract

This invention discloses a synchronous rectification control circuit based on drive voltage pre-modulation technology, including a pre-modulation circuit and a fast turn-off circuit. Before the synchronous rectifier is turned off, when the drain-source voltage of the synchronous rectifier reaches a preset threshold voltage V... TH1 At this time, the pre-modulation circuit adaptively adjusts the gate-source voltage of the synchronous rectifier diode, thereby controlling its drain-source voltage to be maintained at the threshold voltage V. TH1 Nearby; when the drain-source voltage of the synchronous rectifier reaches the preset threshold voltage V TH2 In this case, the fast turn-off circuit quickly pulls down the drain-source voltage to turn off the synchronous rectifier. Therefore, this invention extends the conduction time of the synchronous rectifier through drive voltage pre-modulation technology to avoid premature turn-off caused by parasitic inductance, thereby reducing synchronous rectification losses and improving the efficiency of the switching power supply.

Description

Technical Field

[0001] This invention belongs to the field of switching power supply technology, specifically relating to a synchronous rectification control circuit based on drive voltage pre-modulation technology. Background Technology

[0002] Synchronous rectification is a method of using power MOSFETs with low on-state resistance to replace rectifier diodes in order to reduce rectification losses. The current-voltage characteristic of power MOSFETs when they are turned on is linear. When using power MOSFETs as rectifiers, the gate voltage must be synchronized with the phase of the rectified voltage in order to complete the rectification function.

[0003] In switching power supply systems, synchronous rectification is typically used to improve system conversion efficiency. For example... Figure 1 The diagram shows the structure of a prior art flyback converter, which includes an isolation transformer T, an input capacitor C1 and an output capacitor C0, a primary-side main power transistor M1, a main power transistor control circuit, a secondary-side synchronous rectifier transistor M0, and a pull-down current source I0. The secondary side uses a synchronous rectifier transistor M0 instead of a diode to achieve rectification, thereby reducing rectification losses and improving converter efficiency.

[0004] During the operation of the flyback converter, the PCB trace inductance and package lead inductance will cause the drain-source voltage V of the synchronous rectifier M0 to increase. DS The detected value is greater than the actual value, causing the synchronous rectifier diode M0 to turn off prematurely, resulting in low converter efficiency. To extend the conduction time of the synchronous rectifier diode M0 as much as possible, the conventional approach is as follows: a pull-down current source I0 is connected to the gate of the synchronous rectifier diode M0. When the drain-source voltage V of the synchronous rectifier diode M0 is detected... DS Reaching the preset threshold voltage V TH1 At that time, the gate-source voltage V of the synchronous rectifier M0 is pulled down by the pull-down current source I0. GS Increase the on-resistance R ON Reduce drain-source voltage V DS When the drain-source voltage V of the synchronous rectifier diode M0 is detected... DS Reaching the preset threshold voltage V TH2 When this happens, the gate-source voltage V of the synchronous rectifier M0 is quickly pulled down. GS This is to achieve the shutdown of the synchronous rectifier tube M0.

[0005] Chinese patent application CN109713921A discloses a synchronous rectification control circuit, control method, and switching circuit, such as... Figure 2 The diagram shows the operating waveform of this patented technical solution. It uses a constant pull-down current value for the pull-down current source. When the drain-source voltage V of the synchronous rectifier M0 is detected... DS Reaching the preset threshold voltage V TH1At that time, its gate-source voltage V GS The on-resistance R is significantly pulled low by a constant pull-down current. ON The drain-source voltage V of the synchronous rectifier M0 is relatively large. DS It also decreased significantly, falling below the preset threshold voltage V. TH1 A certain voltage level. However, this solution increases the on-resistance R of the synchronous rectifier. ON An increase in the rectifier size leads to increased rectification losses and decreased converter efficiency.

[0006] Chinese patent application CN212752132U discloses a synchronous rectification control circuit and a switching power supply. To solve the problem of constant pull-down current source value, it uses a variable pull-down current source to control the gate-source voltage V of the synchronous rectifier transistor M0. GS The pull-down current source is composed of multiple resistors and a fixed pull-down current source connected in series. A switching transistor is connected in parallel across each resistor, and each switching transistor is controlled by a comparator circuit. When the gate-source voltage V of the synchronous rectifier M0... GS When the voltage drops to different preset threshold values, the switching transistors are sequentially turned off, continuously reducing the current value of the pull-down current source to achieve a variable pull-down current source. This patented technology can reduce the on-resistance R of the synchronous rectifier diode. ON While reducing rectification losses and improving converter efficiency, the solution employs multiple resistors, switching transistors, and comparator circuits, making the implementation complex and the circuit size large, resulting in higher circuit costs. Summary of the Invention

[0007] In view of the above, the present invention provides a synchronous rectification control circuit based on drive voltage pre-modulation technology, which uses drive voltage pre-modulation technology to control the gate-source voltage V of synchronous rectifier M0. GS Adaptive adjustment is performed to control the drain-source voltage V. DS Maintain at the threshold voltage V TH1 Nearby, the on-time of the synchronous rectifier was extended to avoid premature turn-off caused by parasitic inductance, and the on-resistance R of the synchronous rectifier was reduced. ON This is to reduce synchronous rectification losses and improve the efficiency of switching power supplies.

[0008] A synchronous rectification control circuit based on drive voltage premodulation technology, used to control the synchronous rectifier diodes in a flyback converter, includes:

[0009] The pre-modulation circuit is used to obtain the drain-source voltage V of the synchronous rectifier. DS and compare it with the threshold voltage V TH1 Comparison, when the drain-source voltage V DS Rise to V TH1When the time is right, a pre-modulation signal is output to the gate of the synchronous rectifier to adaptively adjust the gate-source voltage of the synchronous rectifier.

[0010] A fast shutdown circuit is used to obtain the drain-source voltage V of the synchronous rectifier diode. DS and compare it with the threshold voltage V TH2 Comparison, when the drain-source voltage V DS Rise to V TH2 When the gate voltage of the synchronous rectifier is pulled down quickly, a turn-off signal is output to the gate of the synchronous rectifier.

[0011] The control circuit is activated to obtain the drain-source voltage V of the synchronous rectifier diode. DS and compare it with the turn-on threshold voltage V THON Comparison, when the drain-source voltage V DS Below V THON When the synchronous rectifier is activated, an enable signal is output to the gate of the synchronous rectifier to quickly pull up the gate-source voltage of the synchronous rectifier.

[0012] Furthermore, the pre-modulation circuit includes a comparator CMP1, a PMOS transistor M2, and an NMOS transistor M3, wherein the non-inverting input terminal of the comparator CMP1 is connected to the drain-source voltage V. DS The inverting input is connected to the threshold voltage V. TH1 The output terminal is connected to the gate of PMOS transistor M2 and the gate of NMOS transistor M3. The source of PMOS transistor M2 is connected to the power supply voltage VCC. The drain of PMOS transistor M2 is connected to the drain of NMOS transistor M3 and outputs a pre-modulated signal. The source of NMOS transistor M3 is grounded.

[0013] Furthermore, the PMOS transistor M2 is a pull-up switch, and its gate receives the comparison signal V output by comparator CMP1. C1 When comparing signal V C1 When the signal is low, the pull-up switch is in the on state, providing pull-up current, which pulls up the gate-source voltage of the synchronous rectifier through the pre-modulated signal output from the drain.

[0014] Furthermore, the NMOS transistor M3 is a pull-down switch, and its gate receives the comparison signal V output by comparator CMP1. C1 When comparing signal V C1 When the signal is high, the pull-down switch is in the on state, providing pull-down current, which pulls down the gate-source voltage of the synchronous rectifier through the pre-modulated signal output from the drain.

[0015] Furthermore, the fast turn-off circuit includes a comparator CMP2 and an NMOS transistor M4, wherein the non-inverting input of the comparator CMP2 is connected to the drain-source voltage V. DS The inverting input is connected to the threshold voltage V.TH2 The output terminal is connected to the gate of NMOS transistor M4, the drain of NMOS transistor M4 outputs a turn-off signal, and the source of NMOS transistor M4 is grounded.

[0016] Furthermore, the NMOS transistor M4 is a turn-off switch, and its gate receives the comparison signal V output by comparator CMP2. C2 When comparing signal V C2 When the signal is high, the turn-off switch is in the on state, providing a large pull-down current. The turn-off signal output from the drain quickly pulls down the gate-source voltage of the synchronous rectifier, thereby achieving rapid turn-off of the synchronous rectifier.

[0017] Furthermore, the turn-on control circuit includes a comparator CMP0 and a PMOS transistor M1, wherein the non-inverting input terminal of the comparator CMP0 is connected to the drain-source voltage V. DS The inverting input is connected to the turn-on threshold voltage V. THON The output terminal is connected to the gate of PMOS transistor M1, the drain of PMOS transistor M1 outputs the turn-on signal, and the source of PMOS transistor M1 is connected to the power supply voltage VCC.

[0018] Furthermore, the PMOS transistor M1 is a turn-on switch, and its gate receives the comparison signal V output by the comparator CMP0. C0 When comparing signal V C0 When the signal is low, the switching transistor is in the on state, providing a large pull-up current. The turn-on signal output from the drain quickly pulls up the gate-source voltage of the synchronous rectifier, thereby realizing the turn-on control of the synchronous rectifier.

[0019] Preferably, the threshold voltage V TH1 Less than the threshold voltage V TH2 Threshold voltage V TH2 This is the drain-source voltage value corresponding to when the synchronous rectifier is turned off.

[0020] In this invention, before the synchronous rectifier is turned off, when the drain-source voltage of the synchronous rectifier reaches a preset threshold voltage V... TH1 At this time, the pre-modulation circuit adaptively adjusts the gate-source voltage of the synchronous rectifier diode, thereby controlling its drain-source voltage to be maintained at the threshold voltage V. TH1 Nearby; when the drain-source voltage of the synchronous rectifier reaches the preset threshold voltage V TH2 In this case, the fast turn-off circuit quickly pulls down the drain-source voltage to turn off the synchronous rectifier. Therefore, this invention extends the conduction time of the synchronous rectifier through drive voltage pre-modulation technology to avoid premature turn-off caused by parasitic inductance, thereby reducing synchronous rectification losses and improving the efficiency of the switching power supply. Attached Figure Description

[0021] Figure 1This is a block diagram of a flyback converter structure in the prior art.

[0022] Figure 2 This is a schematic diagram of the working waveforms of an existing technology solution.

[0023] Figure 3 This is a structural block diagram of the flyback converter in an embodiment of the present invention.

[0024] Figure 4 This is a schematic diagram of the synchronous rectification control circuit in an embodiment of the present invention.

[0025] Figure 5 This is a schematic diagram of the working waveform of the synchronous rectification control circuit in an embodiment of the present invention. Detailed Implementation

[0026] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] This embodiment is as follows: Figure 3 The flyback converter structure shown is illustrated as an example. The flyback converter includes an isolation transformer T, an input capacitor C1, an output capacitor C0, a primary-side main power transistor M1, a main power transistor control circuit, a secondary-side synchronous rectifier transistor M0, and a synchronous rectification control circuit. This invention designs the synchronous rectification control circuit to maximize the on-time of the synchronous rectifier transistor, thereby avoiding premature turn-off caused by parasitic inductance, reducing synchronous rectification losses, and improving the efficiency of the switching power supply. It should be understood that other switching power supply circuits with synchronous rectification functions are also applicable.

[0028] like Figure 4 The diagram shows a synchronous rectification control circuit based on drive voltage premodulation technology in this embodiment. This synchronous rectification control circuit can be used for, for example... Figure 3 In the flyback converter shown, M0 is a synchronous rectifier diode. The synchronous rectification control circuit in this embodiment mainly includes a turn-on control circuit 1, a pre-modulation circuit 2, and a fast turn-off circuit 3. The turn-on control circuit 1 includes a comparator circuit and a turn-on switching transistor M1. The comparator circuit includes a comparator CMP0, and the input terminals of the comparator CMP0 receive the drain-source voltage V of the synchronous rectifier diode M0. DS and the preset turn-on threshold voltage V THON The non-inverting input of the comparator receives the drain-source voltage V from the synchronous rectifier M0. DS The inverting input receives a preset turn-on threshold voltage V. THON To output the comparison signal V C0 The gate of the switching transistor M1 is turned on to receive the comparison signal V. C0 And based on the comparison signal V C0 Control its on / off state; when the comparison signal V C0When the voltage is low, the switching transistor M1 is in the on state, providing a large pull-up current and quickly raising the gate-source voltage V of the synchronous rectifier transistor M0. GS This enables the turn-on control of the synchronous rectifier diode M0. In this embodiment, the gate of the turn-on switching transistor M1 receives the comparison signal V. C0 The drain is connected to the gate of the synchronous rectifier M0, and the source is connected to the source of the synchronous rectifier M0, i.e., grounded.

[0029] The pre-modulation circuit 2 includes a comparator circuit and a switching transistor circuit. The comparator circuit includes CMP1, and the input terminals of comparator CMP1 receive the drain-source voltage V of the synchronous rectifier transistor. DS and the preset threshold voltage V TH1 The non-inverting input of the comparator receives the drain-source voltage V of the synchronous rectifier M0. DS The inverting input receives a preset threshold voltage V. TH1 To output the comparison signal V C1 To the switching transistor circuit.

[0030] In this embodiment, the switching circuit includes a pull-up switch M2 and a pull-down switch M3. The gate of the pull-up switch M2 receives the comparison signal V. C1 When comparing signal V C1 When the voltage is low, the pull-up switch M2 is in the on state, providing pull-up current and pulling up the gate-source voltage V of the synchronous rectifier M0. GS The gate of pull-down switch M3 receives the comparison signal V. C1 When comparing signal V C1 When the voltage is high, the pull-down switch M3 is in the on state, providing pull-down current and pulling down the gate-source voltage V of the synchronous rectifier M0. GS In this embodiment, the source of the synchronous rectifier M0 is grounded, the source of the pull-up switch M2 is connected to the power supply, and its drain is connected to the gate of the synchronous rectifier M0. The drain of the pull-down switch M3 is connected to the gate of the synchronous rectifier M0, and its source is connected to the source of the synchronous rectifier M0, i.e., grounded.

[0031] In this embodiment, a preset threshold voltage V is used. TH1 Less than the preset threshold voltage V TH2 V TH2 That is, the drain-source voltage value corresponding to when the synchronous rectifier diode M0 is turned off, such as the threshold voltage V. TH2 Set to -5mV, when the drain-source voltage of the synchronous rectifier M0 reaches the preset threshold voltage V. TH2 When the synchronous rectifier diode M0 is turned off, the threshold voltage V... TH1 Set to a value between -40mV and -60mV.

[0032] Fast shutdown circuit 3 includes a comparator circuit and a shutdown switch M4. The comparator circuit includes comparator CMP2, whose input terminals receive the drain-source voltage V of synchronous rectifier M0. DS and the preset threshold voltage V TH2 The non-inverting input of the comparator receives the drain-source voltage V from the synchronous rectifier M0. DS The inverting input receives a preset threshold voltage V. TH2 To output the comparison signal V C2 The switching transistor M4 is turned off to receive the comparison signal V. C2 And based on the comparison signal V C2 Control its on / off state. When the comparison signal V... C2 When the voltage is high, the off-state switch M4 is in the on state, providing a large pull-down current and quickly pulling down the gate-source voltage V of the synchronous rectifier M0. GS This enables the rapid turn-off of the synchronous rectifier diode M0. In this embodiment, the gate of the turn-off switch M4 receives the comparison signal V. C2 The drain is connected to the gate of the synchronous rectifier M0, and the source is connected to the source of the synchronous rectifier M0, i.e., grounded.

[0033] Below we combine Figure 4 The circuit structure of this invention is described in detail, illustrating the specific working principle of the synchronous rectification control circuit. For example... Figure 5 As shown, during the period from t0 to t1, the primary power transistor M1 of the flyback converter is in the on state, while the secondary synchronous rectifier transistor M0 is in the off state, and the secondary current I... SD The value is zero. During the period from t1 to t2, the primary-side switch M1 is turned off, and the secondary-side current I is zero. SD The voltage increases, and freewheeling occurs through the body diode D0 of the synchronous rectifier M0, resulting in a drain-source voltage V of the synchronous rectifier M0. DS The voltage drops to the negative value of the forward voltage drop of the body diode D0. When the drain-source voltage V of the synchronous rectifier M0... DS The voltage is lower than the preset turn-on threshold voltage V THON At that time, the comparator CMP0 outputs the comparison signal V. C0 If the voltage is low, the switching transistor M1 is turned on, quickly raising the gate-source voltage V of the synchronous rectifier transistor M0. GS At time t2, the gate-source voltage VGS of the synchronous rectifier M0 is relatively high, and the secondary current I... SD The current is freewheeled through synchronous rectifier M0, and the drain-source voltage V of synchronous rectifier M0 is... DS The voltage increases, which affects its on-resistance R. ON With drain-source current I DS The product of and . During the period from t2 to t3, the secondary current I SD The drain-source voltage V of the synchronous rectifier diode M0 continues to decrease. DSIt continues to increase. At time t3, the drain-source voltage V... DS Reaching the preset threshold voltage V TH1 The pre-modulation circuit 2 starts outputting a pre-modulation signal to adjust the gate-source voltage V of the synchronous rectifier M0. GS This makes the drain-source voltage V DS Maintain at the preset threshold voltage V TH1 Nearby. The specific process of the pre-modulation stage is as follows: when the drain-source voltage V of the synchronous rectifier M0... DS Slightly greater than the threshold voltage V TH1 At that time, the comparator CMP1 outputs the comparison signal V. C1 If the voltage level is high, then the pull-down switch M3 is in the on state, and the gate-source voltage V of the synchronous rectifier M0 is high. GS Pulled low, the on-state voltage R ON The increase causes the drain-source voltage V to... DS It has decreased somewhat. When the drain-source voltage V of the synchronous rectifier M0... DS Slightly less than the threshold voltage V TH1 At that time, the comparator CMP1 outputs the comparison signal V. C1 When the voltage level is low, the pull-up switch M2 is in the on state, and the gate-source voltage V of the synchronous rectifier M0 is low. GS When pulled high, the on-resistance R ON The decrease causes the drain-source voltage V to drop, resulting in a decrease in the drain-source voltage V. DS The voltage increases somewhat. During the period from t3 to t4, the output pre-modulation signal of the pre-modulation circuit 2 affects the gate-source voltage V of the synchronous rectifier M0. GS Adaptive adjustment is performed to make it exhibit a slow decreasing trend during the pre-modulation stage, thereby controlling the drain-source voltage V. DS Maintain at the preset threshold voltage V TH1 Nearby. At time t4, the secondary current I... SD The drain-source voltage V of the synchronous rectifier M0 drops to near zero. DS Reaching the preset threshold voltage V TH2 At that time, the fast shutdown circuit 3 affects the gate-source voltage V of the synchronous rectifier M0. GS Perform a rapid pull-down, specifically when the drain-source voltage V... DS The voltage is greater than the preset threshold voltage V TH2 At that time, the comparator CMP2 outputs the comparison signal V. C2 When the voltage level is high, the off-state switching transistor is in the on state, providing a large pull-down current and quickly lowering the gate-source voltage V of the synchronous rectifier transistor M0. GS This enables the rapid turn-off of the synchronous rectifier diode M0. During the period from t4 to t5, the synchronous rectifier diode M0 is in the off state, and the secondary current I... SD Only a small amount remains, completing the final freewheeling through the body diode D0 of the synchronous rectifier M0. The drain-source voltage V of the synchronous rectifier M0...DS It drops to the negative value of the forward voltage drop of the body diode D0.

[0034] Comparison of the operating waveforms of the synchronous rectification control circuit in this embodiment Figure 2 The operating waveform of the existing solution shows that, due to the use of a constant current pull-down current source, the existing technology cannot control the gate-source voltage V of the synchronous rectifier M0. GS Adaptive adjustment leads to gate-source voltage V GS The on-resistance R is pulled down significantly. ON The drain-source voltage V of the synchronous rectifier M0 is relatively large. DS Below the preset threshold voltage V TH1 A certain voltage level leads to increased rectification losses and reduced converter efficiency. In this embodiment, however, the gate-source voltage V of the synchronous rectifier M0 is modulated by a pre-modulated signal. GS Adaptive adjustment is performed to control the drain-source voltage V. DS Maintaining the voltage near the threshold voltage reduces the on-resistance R. ON This reduces rectification losses. In summary, the drive voltage pre-modulation technology of this invention extends the conduction time of the synchronous rectifier tube to avoid premature turn-off caused by parasitic inductance, thereby reducing synchronous rectification losses and improving the efficiency of the switching power supply.

[0035] Those skilled in the art will recognize that the synchronous rectification control circuit of the present invention is not limited to the switching power supply method shown in the above embodiments. The synchronous rectification control circuit of the present invention can be applied to the field of switching power supplies with the same technical problems.

[0036] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. Those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. A synchronous rectification control circuit based on driving voltage pre-modulation technique for controlling a synchronous rectifier in a flyback converter, characterized in that, The synchronous rectification control circuit comprises: The pre-modulation circuit is used to obtain the drain-source voltage V of the synchronous rectifier. DS and compare it with the threshold voltage V TH1 Comparison, when the drain-source voltage V DS Rise to V TH1 When the time is right, a pre-modulation signal is output to the gate of the synchronous rectifier to adaptively adjust the gate-source voltage of the synchronous rectifier. A fast shutdown circuit is used to obtain the drain-source voltage V of the synchronous rectifier diode. DS and compare it with the threshold voltage V TH2 Comparison, when the drain-source voltage V DS Rise to V TH2 When the gate voltage of the synchronous rectifier is pulled down quickly, a turn-off signal is output to the gate of the synchronous rectifier. The control circuit is activated to obtain the drain-source voltage V of the synchronous rectifier diode. DS and compare it with the turn-on threshold voltage V THON Comparison, when the drain-source voltage V DS Below V THON When the gate voltage of the synchronous rectifier is pulled up quickly, an on signal is output to the gate of the synchronous rectifier. The pre-modulation circuit includes a comparator CMP1, a PMOS transistor M2, and an NMOS transistor M3, wherein the non-inverting input terminal of the comparator CMP1 is connected to the drain-source voltage V. DS The inverting input is connected to the threshold voltage V. TH1 The output terminal is connected to the gate of PMOS transistor M2 and the gate of NMOS transistor M3. The source of PMOS transistor M2 is connected to the power supply voltage VCC. The drain of PMOS transistor M2 is connected to the drain of NMOS transistor M3 and outputs a pre-modulated signal. The source of NMOS transistor M3 is grounded. The threshold voltage V TH1 Less than the threshold voltage V TH2 Threshold voltage V TH2 This is the drain-source voltage value corresponding to when the synchronous rectifier is turned off.

2. The synchronous rectification control circuit of claim 1, wherein: The PMOS transistor M2 is a pull-up switch, and its gate receives the comparison signal V output by comparator CMP1. C1 When comparing signal V C1 When the signal is low, the pull-up switch is in the on state, providing pull-up current, which pulls up the gate-source voltage of the synchronous rectifier through the pre-modulated signal output from the drain.

3. The synchronous rectification control circuit of claim 1, wherein: The NMOS transistor M3 is a pull-down switch, and its gate receives the comparison signal V output by comparator CMP1. C1 When comparing signal V C1 When the signal is high, the pull-down switch is in the on state, providing pull-down current, which pulls down the gate-source voltage of the synchronous rectifier through the pre-modulated signal output from the drain.

4. The synchronous rectification control circuit of claim 1, wherein: The fast turn-off circuit includes a comparator CMP2 and an NMOS transistor M4, wherein the non-inverting input of the comparator CMP2 is connected to the drain-source voltage V. DS The inverting input is connected to the threshold voltage V. TH2 The output terminal is connected to the gate of NMOS transistor M4, the drain of NMOS transistor M4 outputs a turn-off signal, and the source of NMOS transistor M4 is grounded.

5. The synchronous rectification control circuit of claim 4, wherein: The NMOS transistor M4 is a turn-off switch, and its gate receives the comparison signal V output by comparator CMP2. C2 When comparing signal V C2 When the signal is high, the turn-off switch is in the on state, providing a large pull-down current. The turn-off signal output from the drain quickly pulls down the gate-source voltage of the synchronous rectifier, thereby achieving rapid turn-off of the synchronous rectifier.

6. The synchronous rectification control circuit according to claim 1, characterized in that: The turn-on control circuit includes a comparator CMP0 and a PMOS transistor M1, wherein the non-inverting input terminal of the comparator CMP0 is connected to the drain-source voltage V. DS The inverting input is connected to the turn-on threshold voltage V. THON The output terminal is connected to the gate of PMOS transistor M1, the drain of PMOS transistor M1 outputs the turn-on signal, and the source of PMOS transistor M1 is connected to the power supply voltage VCC.

7. The synchronous rectification control circuit of claim 6, wherein: The PMOS transistor M1 is a turn-on switch, and its gate receives the comparison signal V output by comparator CMP0. C0 When comparing signal V C0 When the signal is low, the switching transistor is in the on state, providing a large pull-up current. The turn-on signal output from the drain quickly pulls up the gate-source voltage of the synchronous rectifier, thereby realizing the turn-on control of the synchronous rectifier.

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