CN114567189A - Self-adaptive synchronous rectification control circuit and control method - Google Patents

Abstract

The invention discloses a self-adaptive synchronous rectification control circuit and a control method, comprising the following steps: the device comprises a quick starting module, a self-adaptive turn-off module, an oscillation shielding module and a driving module. The input of the quick opening module is a synchronous rectification power tube S₁Drain-source voltage V of_DSAnd the output is an opening control signal SET _ PRE; the input of the self-adaptive turn-off module is a synchronous rectification power tube S₁Drain-source voltage V of_DSAnd outputs a turn-off control signal RST _ PRE; the input of the oscillation shielding module is a minimum on-time control signal and a minimum off-time control signal, the input signal also comprises an on control signal SET _ PRE and an off control signal RST _ PRE, and the output is a synchronous rectification power tube S without driving capability₁A control signal Q; the input of the driving module is a synchronous rectification power tube S without driving capability₁The output of the control signal Q is a synchronous rectification power tube S with driving capability₁Control signal V_GS。

Description

Self-adaptive synchronous rectification control circuit and control method

Technical Field

The invention relates to the technical field of power integrated circuits, in particular to a self-adaptive synchronous rectification control circuit and a control method.

Background

With the continuous development of technologies such as electric vehicles, big data, artificial intelligence and the like, the requirements on power converters are also continuously increased. Currently, the demand for power converters is moving towards high power densities. To increase power density, the frequency of the power switches is continuously increased. The switching frequencies of currently mainstream high frequency power converters have reached the order of 1MHz, and there is a trend towards higher switching frequencies. Meanwhile, in the high frequency power converter, a Synchronous rectification technology (abbreviated as SR) is generally used to replace the conventional diode rectification to improve the rectification efficiency, as shown in fig. 1 and 2.

One of the challenges in increasing the switching frequency is that most conventional synchronous rectifier controllers are generally only suitable for lower switching frequencies (< 500 KHz). The reason that the traditional SR controller cannot be used for higher switching frequency is that the current SR controller mainly rectifies the power tube S by sampling₁Drain-source voltage V of_DSControl is achieved in a manner that can cause early turn-off problems and turn-on delay problems in high frequency power converters. More specifically, higher switching frequency means larger current slope di/dt, and MOS package parasitic inductance and PCB parasitic inductance Ls generate V at large di/dt_DSThe phase of the voltage is advanced, so that the SR controller triggers a turn-off threshold too early, and the synchronous rectification power tube S is turned off in advance₁As shown in fig. 3. Whereas the conventional opening control is via V_DSThe body diode conduction is detected before the turn-on control signal is generated, which results in the body diode conduction a period of time before the turn-on, which is more significant in the high frequency converter as shown in fig. 4.

Aiming at the problem of early turn-off and turn-on delay of the traditional SR controller, the invention provides a novel control scheme, which effectively solves the problem of synchronous rectification power tube S₁The problem of delay of turn-off and turn-on in advance is solved, and the working frequency and efficiency of the system are improved.

Disclosure of Invention

In view of the above, the present invention provides a self-adaptive synchronous rectification control circuit and a control method thereof, which can effectively solve the problems of early turn-off and turn-on delay and are suitable for future power converters with higher switching frequency.

In order to achieve the purpose, the invention adopts the following technical scheme:

an adaptive synchronous rectification control circuit, the control circuit comprising:

a fast turn-on module with an input of a synchronous rectification power tube S₁Drain-source voltage V of_DSThe output is an opening control signal SET _ PRE;

an adaptive turn-off module with synchronous rectification power tube S as input₁Drain-source voltage V of_DSThe output of which is a turn-off control signal RST _ PRE;

an oscillation shielding module with input of a minimum ON-time control signal MIN _ ON and a minimum OFF-time control signal MIN _ OFF, and the ON control signal SET _ PRE and the OFF control signal RST _ PRE, and output of a synchronous rectification power tube S without driving capability₁Control signal Q, and control signal QB;

a driving module having the synchronous rectification power tube S without driving capability as its input₁A control signal Q whose output is a synchronous rectification power tube S with driving capability₁Control signal V_GS。

Further, the quick opening module specifically includes: capacitor C₁Resistance R₁Voltage reference V_biasComparator CMP1, schmitt trigger SHMT1, AND gate AND 1;

the capacitor C₁Resistance R₁And a voltage reference V_biasForm a high-pass network, the input end of the high-pass network is the capacitor C₁At one end of which the sampled drain-source voltage V is connected_DS；

The resistor R₁Is connected to the voltage reference V_biasAnd the voltage reference V_biasThe negative terminal of (2) is grounded;

the capacitor C₁And the resistance R₁Are connected to the input terminal of the Schmitt trigger SHMT1, the output of the Schmitt trigger SHMT1 is the drain-source voltage V_DSThe falling edge slope of (1);

the negative input terminal of the comparator CMP1 receives the sampled drain-source voltage V_DSThe positive input end of the comparator CMP1 is connected with the turn-on threshold voltage V _ TON, and the output of the comparator CMP1 is used as the judgment result of the turn-on threshold;

the AND gate AND1 has inputs of the comparator CMP1 AND the output of the schmitt trigger SHMT1, AND has an output of the on control signal SET _ PRE.

Further, the start control signal SET _ PRE is generated only when 2 conditions are satisfied, wherein the first condition is the sampled drain-source voltage V_DSLess than an opening threshold V _ TON, the second condition being that V is detected_DSThe falling edge slope of (d) reaches a certain value.

Further, the adaptive shutdown module specifically includes: comparator CMP2, AND gate AND2, switch M1, switch M2, AND current reference I_biasCapacitor C₂A sample-and-hold circuit SH, a PI compensator, and a comparator CMP 3;

the comparator CMP2, the negative terminal of which receives the drain-source voltage V_DSWith a positive side of the threshold value V_TThe output end of the AND gate is connected with the input end of the AND gate AND 2;

the input end of the AND gate AND2 also receives a control signal QB, AND the output end of the AND gate AND2 controls the switch M2 to be switched on AND offTo control the current reference I_biasFor the capacitor C₂Charging is carried out, wherein the capacitor C₂One end of the switch is grounded, and the other end of the switch is connected with the switch M1, the switch M2 and the input end of the sample-and-hold circuit SH respectively;

the sample-and-hold circuit SH is used for controlling the capacitor C under the control of a control signal Q₂And the control signal Q also controls the switch M1 to switch the capacitor C₂Voltage V of_C2Carrying out periodic zero clearing, wherein the output end of the sampling hold circuit SH is connected with the inverting input end of the PI compensator;

the non-inverting input of the PI compensator is connected with a voltage reference V_REFAn output terminal thereof is V _ TOFF, and the V _ TOFF is output to an inverting input terminal of the comparator CMP 3;

the comparator CMP3 has its non-inverting input terminal receiving the drain-source voltage V_DSThe output is the turn-off control signal RST _ PRE, which is used as a turn-off control signal for synchronous rectification control.

Further, the oscillation shielding module specifically includes: the circuit comprises a minimum turn-off shielding circuit, a minimum turn-on shielding circuit, an AND gate AND3, an AND gate AND4 AND an RS trigger;

the minimum OFF-time control signal MIN _ OFF is input to the minimum OFF-time mask circuit, AND an output terminal of the minimum OFF-time mask circuit is connected to an input terminal of the AND gate AND3, wherein the input terminal of the AND gate AND3 further receives the on-control signal SET _ PRE;

the minimum-ON mask circuit has an input of the minimum ON-time control signal MIN _ ON AND an output connected to an input of the AND gate AND4, wherein the input of the AND gate AND4 further receives an off control signal RST _ PRE;

the output signal of the AND gate AND3 is SET, AND the output signal of the AND gate AND4 is RST, wherein the signal SET controls the setting of the RS flip-flop, AND the signal RST controls the resetting of the RS flip-flop;

the output of the RS trigger is a control signal Q and a control signal QB.

An adaptive synchronous rectification control method, comprising the steps of:

step S1, setting a threshold, including: first by detecting V_DSTo obtain the synchronous rectification power tube S in each period₁On-time t of body diode after turn-off_diodeThen the on-time t is set_diodeConverted into corresponding voltage signal V_dThen the voltage signal V is applied_dAs the input signal of the inverting terminal of the PI compensator, the output V _ TOFF of the PI compensator is used as the synchronous rectification power tube S₁A threshold value of turn-off, wherein the input of the non-inverting terminal of the PI compensator is a reference voltage V_REF；

Step S2, adaptive turn-off threshold control, including: obtaining V in real time_DSThen, through the comparator, compare the V_DSAnd V _ TOFF when V_DSWhen the voltage is greater than or equal to V _ TOFF, generating a turn-off control signal RST _ PRE;

step S3, the quick activation control includes: real-time acquisition of V by detection_DSIf it reaches the SET threshold V _ TON, the start control signal SET _ PRE is generated.

The invention has the beneficial effects that:

the invention provides a new control method based on the traditional SR controller. The control method comprises two core contents, namely self-adaptive turn-off threshold control and quick turn-on control.

The structure of the invention does not need additional components and parts, and can effectively reduce the volume of the system. And the invention adopts a full integration scheme and can be applied to the current high-frequency converter and a future higher-frequency power converter.

Drawings

FIG. 1 is a schematic diagram of a conventional diode rectifier described in the background art;

FIG. 2 is a diagram illustrating synchronous rectification control described in the background art;

FIG. 3 is a waveform diagram illustrating the early turn-off principle described in the background art;

FIG. 4 is a waveform diagram illustrating the principle of turn-on delay described in the background art;

fig. 5 is a block diagram of an adaptive synchronous rectification control circuit provided in embodiment 1;

fig. 6 is a schematic diagram of a specific structure of an adaptive synchronous rectification control circuit provided in embodiment 1.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

Referring to fig. 5 and 6, the present embodiment provides an adaptive synchronous rectification control circuit, including:

a fast turn-on module with an input of a synchronous rectification power tube S₁Drain-source voltage V of_DSThe output is an opening control signal SET _ PRE;

an adaptive turn-off module with synchronous rectification power tube S as input₁Drain-source voltage V of_DSAn output thereof is a turn-off control signal RST _ PRE;

an oscillation shielding module with input of a minimum ON-time control signal MIN _ ON and a minimum OFF-time control signal MIN _ OFF, and the ON control signal SET _ PRE and the OFF control signal RST _ PRE, and output of a synchronous rectification power tube S without driving capability₁A control signal Q;

a driving module having the synchronous rectification power tube S without driving capability as its input₁A control signal Q whose output is a synchronous rectification power tube S with driving capability₁Control signal V_GS。

Specifically, in this embodiment, the fast turn-on module is detecting the body diodeAfter the power is conducted, a starting control signal SET _ PRE is immediately generated, and the synchronous rectification power tube S is started after shielding by the minimum turn-off time₁. The self-adaptive turn-off module detects the secondary side current I_sWhen the voltage is equal to or close to 0, a turn-off control signal RST _ PRE is immediately generated, and the synchronous rectification power tube S is turned off after shielding of the minimum turn-on time₁. The oscillation mask module may program the mask time by a minimum ON time control signal MIN _ ON and a minimum OFF time control signal MIN _ OFF. The driving module converts an input control signal Q without driving capability into a control signal V with driving capability_GSIn combination with V_DSControlling synchronous rectification power tube S₁。

Specifically, in this embodiment, the quick opening module specifically includes: capacitor C₁Resistance R₁Voltage reference V_biasComparator CMP1, schmitt trigger SHMT1, AND gate AND 1;

the capacitor C₁And a resistor R₁And a voltage reference V_biasForm a high-pass network, the input end of the high-pass network is the capacitor C₁The input end is connected with the sampled drain-source voltage V_DS；

The resistor R₁Is connected to the voltage reference V_biasAnd the voltage reference V_biasThe negative terminal of (2) is grounded;

the capacitor C₁And the resistance R₁Are connected to the input terminal of the Schmitt trigger SHMT1, the output of the Schmitt trigger SHMT1 is the drain-source voltage V_DSThe falling edge slope of (1);

the negative input terminal of the comparator CMP1 receives the sampled drain-source voltage V_DSThe positive input end of the comparator is connected with the starting threshold voltage V _ TON, and the output of the comparator CMP1 is used as the judgment result of the starting threshold;

the AND gate AND1, whose inputs are the outputs of the comparator CMP1 AND the schmitt trigger SHMT1, AND whose output is the on control signal SET _ PRE;

more specifically, in this embodimentIn an example, to avoid false triggering, the turn-on control signal SET _ PRE is generated when 2 conditions are satisfied, where the condition 1 is the sampled drain-source voltage V_DSLess than the turn-on threshold V _ TON, condition 2 is that V is detected_DSThe falling edge slope of (d) reaches a certain value.

More specifically, in the present embodiment, R₁And C₁Composed high-pass network in detection V_DSOn the falling edge, a negative voltage is generated, so that the invention introduces a DC voltage bias V_biasAnd the reliability of the single power supply system is ensured.

The fast turn-on module generates the turn-on control signal SET _ PRE and outputs it to the oscillation shielding module.

Specifically, in this embodiment, the input of the adaptive turn-off module is a sampled drain-source voltage V_DSUpon detecting QB high, the output of the comparator CMP2 will reflect the synchronous rectification power tube S₁Body diode D after turn-off₁On-time length t of_diode。

At t_diodeWithin time, current source I_biasTo the capacitor C₂And charging is carried out. At t_diodeAfter the time, the capacitor C₂Upper voltage V_c2I.e. reflect t_diode。V_c2As input of the sample hold circuit, and finishes sampling under the control of the sampling clock Q to obtain a sampling result V_d. The PI compensator in fig. 6 is a prior art, and includes an error amplification module and a compensation network. The input signal of the inverting terminal of the PI compensator is V_dThe input signal of the in-phase terminal is the reference voltage VREF, and the output signal is the turn-off threshold value V _ TOFF. When the adaptive turn-off module detects V_DSWhen the voltage is more than or equal to V _ TOFF, the turn-off control signal RST _ PRE is immediately generated. In steady state, reference voltage VREF and capacitance C₂And a current source I_biasDetermines the turn-on time t of the reference diode_dioderef：

By negative feedback loop formed by PI compensator_dAdjust to equal VREF, i.e., t_diodeAdjust to and t_dioderefAre equal to, and t_dioderefUsually set to 0 or a very small value. The above process, i.e. the adaptive turn-off control, and the parasitic inductance L_sThe size is irrelevant.

More specifically, in this embodiment, the adaptive turn-off module specifically includes: comparator CMP2, AND gate AND2, switch M1, switch M2, current reference Ibias, AND capacitor C₂A sample-and-hold circuit SH, a PI compensator, and a comparator CMP 3;

the comparator CMP2, the negative terminal of which receives the drain-source voltage V_DSWith a positive side of the threshold value V_TThe output end of the AND gate is connected with the input end of the AND gate AND 2;

the input of the AND gate AND2 also receives a signal QB, the output of which controls the switching AND closing of the switch M2 to control the current reference I_biasFor the capacitor C₂Charging is performed, wherein one end of the switch M2 is grounded, and the other end is connected to the input ends of the switch M1, the switch M2 and the sample-and-hold circuit SH;

the sample-and-hold circuit SH, under control of the signal Q, couples the capacitor C₂And this signal Q also controls the switch M1 to switch the capacitor C₂Voltage V of_C2Carrying out periodic zero clearing, wherein the output end of the sampling hold circuit SH is connected with the inverting input end of the PI compensator;

the non-inverting input of the PI compensator is connected with a voltage reference V_REFAn output terminal thereof is V _ TOFF, and the V _ TOFF is output to an inverting input terminal of the comparator CMP 3;

the comparator CMP3 has a non-inverting input terminal receiving the drain-source voltage V_DSThe output thereof is the turn-off control signal RST _ PRE, which is used as a turn-off control signal for synchronous rectification control.

More specifically, in the present embodiment, the signal Q is output from the oscillation shielding module, and the signal QB is the inverse signal thereof.

Specifically, in this embodiment, the oscillation shielding module specifically includes: the minimum turn-off shielding circuit Min _ off shielding, the minimum turn-on shielding circuit Min _ on shielding, an AND gate AND3, an AND gate AND4 AND an RS trigger; the minimum OFF mask circuit Min _ OFF masking has an input of the minimum OFF time control signal Min _ OFF AND an output connected to an input of the AND gate AND3, wherein the input of the AND gate AND3 further receives the on control signal SET _ PRE; the minimum ON-mask circuit Min _ ON has an input of the minimum ON-time control signal Min _ ON AND an output of the minimum ON-mask circuit Min _ ON connected to an input of the AND gate AND4, wherein the input of the AND gate AND4 further receives an off control signal RST _ PRE; the output signal of the AND gate AND3 is SET, the AND gate AND4 is RST, wherein the SET controls the setting of the RS trigger, AND the RST controls the resetting of the RS trigger; the output of the RS flip-flop is a signal Q and a signal QB.

More specifically, in this embodiment, the oscillation shielding module has 4 input signals, which are: the turn-ON control signal SET _ PRE, the turn-OFF control signal RST _ PRE, the minimum ON-time control signal MIN _ ON, and the minimum OFF-time control signal MIN _ OFF. The oscillation shielding module also has 1 output signal, i.e. no driving capability control signal Q. The function of the oscillation shielding module is to avoid false triggering of the comparator CMP1 or CMP 3. Specifically, in the synchronous rectification power tube S₁When the switch is turned on or off, the drain-source voltage V is caused_DSHigh frequency oscillations are generated, causing spurious toggling of the comparator CMP1 or CMP 3. Therefore, the minimum on-time t needs to elapse after receiving the signal SET _ PRE or RST _ PRE_minonOr minimum off-time t_minoffThen the Q can be set high or low. The programmable port provides a minimum ON-time control signal MIN _ ON and a minimum OFF-time control signal MIN _ OFF by externally connecting the element resistor, and further provides the minimum ON-time t_minonOr minimum off-time t_minoffAnd (6) adjusting.

Specifically, in this embodiment, the driving module is the prior art, and is not described herein again. With an input signal ofThe control signal Q without driving capability is output as a control signal V with driving capability_GS。

Example 2

The embodiment also provides a self-adaptive synchronous rectification control method, which comprises the following steps:

step S1, setting a threshold value, including: first by detecting V_DSTo obtain the synchronous rectification power tube S in each period₁On-time t of body diode after turn-off_diodeThen the on-time t_diodeConverted into corresponding voltage signal V_dThen the voltage signal V is applied_dAs the input signal of the inverting terminal of the PI compensator, the output V _ TOFF of the PI compensator is used as the synchronous rectification power tube S₁A threshold value of turn-off, wherein the input of the non-inverting terminal of the PI compensator is a reference voltage V_REF；

Step S2, adaptive turn-off threshold control, including: obtaining V in real time_DSThen, the V is compared by a comparator_DSAnd V _ TOFF when V_DSWhen the voltage is greater than or equal to V _ TOFF, generating a turn-off control signal RST _ PRE;

step S3, fast start control, including: real-time acquisition of V by detection_DSIf it reaches the SET threshold V _ TON, the start control signal SET _ PRE is generated.

Specifically, since the conventional SR controller is based on V_DSThe sampling control mode has low switching frequency in application occasions, so that the problems of early turn-off and turn-on delay are not obvious. When the traditional SR controller is used for higher switching frequency (more than or equal to 500KHz), the problem of early turn-off and turn-on delay is not negligible, and the efficiency of the power converter is greatly influenced. In order to solve the problem of early shutdown, some techniques have been proposed. The RC network compensation mode achieves certain effect, but the method is greatly influenced by device parameter deviation and does not fundamentally solve the problem. And the RC network compensation mode needs additional external devices, which is not favorable for improving the power density. There is also a pressing need to be addressed for the start-up delay problem, but few studies are currently involved.

In summary, the present invention provides a new control method based on the conventional SR controller. The proposed control method comprises two core contents, namely adaptive off threshold control and fast on control. Adaptive turn-off threshold control by detection V_DSObtain S in each period₁On-time t of body diode after turn-off_diodeAnd will t_diodeConverted into corresponding voltage signal V_dWill V_dAs the input signal of the inverting terminal of the PI (proportional integral) compensator, the output V _ TOFF of the PI compensator is taken as S₁A threshold value of turn-off. When the adaptive turn-off module detects V_DSWhen the voltage is greater than or equal to V _ TOFF, a shutdown control signal RST _ PRE is generated. The in-phase end of the PI compensator is a reference voltage V_REFIt is compared with the diode conduction time t expected by design_dioderefAnd (4) correlating. By the self-adaptive turn-off threshold control method, the problem of early turn-off can be effectively solved. Fast turn-on control by detection V_DSIf the falling edge reaches the SET threshold V _ TON, and the above-mentioned turn-on condition is satisfied, the turn-on control signal SET _ PRE is generated.

The structure of the invention does not need additional components and parts, and can effectively reduce the volume of the system. And the invention adopts a full integration scheme and can be applied to the current high-frequency converter and the future higher-frequency power converter.

The invention is not described in detail, but is well known to those skilled in the art.

The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.

Claims (6)

1. An adaptive synchronous rectification control circuit, the control circuit comprising:

a fast turn-on module with synchronous rectification power tube S as input₁Drain-source voltage V of_DSThe output is an opening control signal SET _ PRE;

an adaptive turn-off module with synchronous rectification power tube S as input₁Drain-source voltage V of_DSThe output of which is a turn-off control signal RST _ PRE;

an oscillation shielding module with input of a minimum ON-time control signal MIN _ ON and a minimum OFF-time control signal MIN _ OFF, and the ON control signal SET _ PRE and the OFF control signal RST _ PRE, and output of a synchronous rectification power tube S without driving capability₁Control signal Q, and control signal QB;

a driving module having the synchronous rectification power tube S without driving capability as its input₁A control signal Q whose output is a synchronous rectification power tube S with driving capability₁Control signal V_GS。

2. The adaptive synchronous rectification control circuit of claim 1, wherein the fast turn-on module specifically comprises: capacitor C₁Resistance R₁Voltage reference V_biasComparator CMP1, schmitt trigger SHMT1, AND gate AND 1;

the capacitor C₁And a resistor R₁And a voltage reference V_biasForm a high-pass network, the input end of the high-pass network is the capacitor C₁The input end is connected with the sampled drain-source voltage V_DS；

The resistor R₁Is connected to the voltage reference V_biasAnd the voltage reference V_biasThe negative terminal of (2) is grounded;

the capacitor C₁And the resistance R₁Are connected to the input terminal of the Schmitt trigger SHMT1, the output of the Schmitt trigger SHMT1 is the drain-source voltage V_DSThe falling edge slope of (1);

the negative input terminal of the comparator CMP1 receives the sampled drain-source voltage V_DSWhich is right beforeThe input end is connected with a starting threshold voltage V _ TON, and the output of the comparator CMP1 is used as the judgment result of the starting threshold;

the AND gate AND1 has inputs of the comparator CMP1 AND the output of the schmitt trigger SHMT1, AND has an output of the on control signal SET _ PRE.

3. The adaptive synchronous rectification control circuit as claimed in claim 2, wherein the start control signal SET PRE is generated when 2 conditions are satisfied simultaneously, wherein the first condition is a sampled drain-source voltage V_DSLess than an opening threshold V _ TON, the second condition being that V is detected_DSThe falling edge slope of (d) reaches a certain value.

4. The adaptive synchronous rectification control circuit according to claim 3, wherein the adaptive turn-off module specifically comprises: comparator CMP2, AND gate AND2, switch M1, switch M2, AND current reference I_biasCapacitor C₂A sample-and-hold circuit SH, a PI compensator, and a comparator CMP 3;

the comparator CMP2, the negative terminal of which receives the drain-source voltage V_DSWith a positive side of the threshold value V_TThe output end of the AND gate is connected with the input end of the AND gate AND 2;

the input of the AND gate AND2 also receives a control signal QB, the output of which controls the current reference I by controlling the switching AND closing of the switch M2_biasFor the capacitor C₂Charging is carried out, wherein the capacitor C₂One end of the switch is grounded, and the other end of the switch is connected with the switch M1, the switch M2 and the input end of the sample-and-hold circuit SH respectively;

the sample-and-hold circuit SH controls the capacitor C under the control of a control signal Q₂And the control signal Q also controls the switch M1 to switch the capacitor C₂Voltage V of_C2Carrying out periodic zero clearing, wherein the output end of the sampling hold circuit SH is connected with the inverting input end of the PI compensator;

the PI compensator having a non-inverting inputTerminated voltage reference V_REFAn output terminal thereof is V _ TOFF, and the V _ TOFF is output to an inverting input terminal of the comparator CMP 3;

the comparator CMP3 has its non-inverting input terminal receiving the drain-source voltage V_DSThe output is the turn-off control signal RST _ PRE, which is used as a turn-off control signal for synchronous rectification control.

5. The adaptive synchronous rectification control circuit according to claim 4, wherein the oscillation shielding module specifically comprises: the circuit comprises a minimum turn-off shielding circuit, a minimum turn-on shielding circuit, an AND gate AND3, an AND gate AND4 AND an RS trigger;

the minimum OFF-time control signal MIN _ OFF is input to the minimum OFF-time mask circuit, AND an output terminal of the minimum OFF-time mask circuit is connected to an input terminal of the AND gate AND3, wherein the input terminal of the AND gate AND3 further receives the on-control signal SET _ PRE;

the minimum-ON mask circuit has an input of the minimum ON-time control signal MIN _ ON AND an output connected to an input of the AND gate AND4, wherein the input of the AND gate AND4 further receives an off control signal RST _ PRE;

the output signal of the AND gate AND3 is SET, AND the output signal of the AND gate AND4 is RST, wherein the signal SET controls the setting of the RS flip-flop, AND the signal RST controls the resetting of the RS flip-flop;

the output of the RS trigger is a control signal Q and a control signal QB.

6. An adaptive synchronous rectification control method is characterized by comprising the following steps:

step S1, setting a threshold value, including: first by detecting V_DSTo obtain the synchronous rectification power tube S in each period₁On-time t of body diode after turn-off_diodeThen the on-time t_diodeConverted into corresponding voltage signal V_dThen the voltage signal V is applied_dAs the input signal of the inverse phase terminal of the PI compensatorOutput V _ TOFF of PI compensator as synchronous rectification power tube S₁A threshold value of turn-off, wherein the input of the non-inverting terminal of the PI compensator is a reference voltage V_REF；

Step S2, adaptive turn-off threshold control, including: obtaining V in real time_DSThen, the V is compared by a comparator_DSAnd V _ TOFF when V_DSWhen the voltage is greater than or equal to V _ TOFF, generating a turn-off control signal RST _ PRE;

step S3, fast start control, including: real-time acquisition of V by detection_DSIf it reaches the SET threshold V _ TON, the start control signal SET _ PRE is generated.

Images