Synchronous rectification controller and flyback converter

Abstract

According to the synchronous rectification controller and the flyback converter provided by the utility model, in each switching period, a driving signal controls a damping circuit to be connected to two ends of a secondary winding at the end moment of follow current of a synchronous rectification tube and controls the damping circuit to be disconnected from the secondary winding at the start moment of secondary conduction of the synchronous rectification tube; and meanwhile, the driving signal drives the synchronous rectifier tube to be conducted for the first time to follow current and conducted for the second time in a switching period so as to realize zero-voltage starting of the primary side main power tube. The synchronous rectification controller provided by the utility model is integrated with the damping circuit, and the damping circuit is used for damping oscillation when the main power tube and the synchronous rectification tube are turned off, reducing the resonance amplitude, and improving the EMC characteristic of the flyback converter. Wherein the synchronous rectification controller shares the same driving signal and simultaneously controls the on-off of the synchronous rectification tube and whether the damping circuit is connected to the two ends of the secondary winding of the flyback converter, so that the control logic and the structure setting of the synchronous rectification controller are greatly simplified.

Description

Technical Field

[0001] The utility model belongs to the technical field of power electronics, and in particular relates to a synchronous rectification controller and a flyback converter. Background Art

[0002] As the part that is most closely connected to the power grid, the switching power supply needs to have good adaptability to external electromagnetic interference on the one hand, and reduce interference to the power grid and surrounding electronic equipment on the other hand. Therefore, the switching power supply needs to have good EMC (electromagnetic compatibility) characteristics.

[0003] The phenomenon that electronic equipment interferes with surrounding electronic equipment when working is called EMI (electromagnetic interference). Electromagnetic interference has many hazards, such as affecting the performance of electronic equipment, causing harmonic pollution in the power grid and thus interfering with other electronic equipment on the power grid. Severe electromagnetic interference can cause high voltage breakdown or burning of electronic equipment.

[0004] Since there are many parasitic capacitors in the ZVS flyback switching power supply system, when the ZVS flyback switching power supply system works in DCM mode (discontinuous mode), the LC oscillation circuit composed of parasitic capacitors and coils will produce harmonic oscillation when the main switch tube and the synchronous rectifier tube are turned off, thereby deteriorating the EMC characteristics of the ZVS flyback switching power supply system. Utility Model Content

[0005] In order to solve the technical problem that the EMC characteristics of the ZVS flyback switching power supply in the prior art are poor, the utility model proposes a synchronous rectification controller and a flyback converter, the synchronous rectification controller comprising:

[0006] A first drive circuit, wherein the first drive circuit generates a drive signal to control the synchronous rectifier in the flyback converter to be turned on twice in each switching cycle, wherein the synchronous rectifier is turned on once for freewheeling, and the synchronous rectifier is turned on twice to achieve zero voltage turn-on of the primary main power tube in the next switching cycle; in particular, the synchronous rectifier controller further includes:

[0007] A damping circuit, a second driving circuit, a first connection end and a second connection end, wherein the first connection end is connected to the drain of the synchronous rectifier tube, and the second connection end is connected to the output end of the flyback converter.

[0008] In each switching cycle, the second drive circuit controls the damping circuit to be connected between the first connection end and the second connection end at the end of the freewheeling of the synchronous rectifier according to the drive signal, and controls the damping circuit to be disconnected from the first connection end and the second connection end at the start of the secondary conduction of the synchronous rectifier.

[0009] Furthermore, in each switching cycle, the second drive circuit controls the damping circuit to be connected between the first connection end and the second connection end within the first time period and when the voltage of the first connection end is greater than the voltage of the second connection end according to the drive signal, the voltage of the first connection end and the voltage of the second connection end, wherein the end time of the freewheeling of the synchronous rectifier is the starting point of the first time period, and the start time of the secondary conduction of the synchronous rectifier is the end point of the first time period.

[0010] Preferably, the output end of the first drive circuit is connected to the gate of the synchronous rectifier and the input end of the second drive circuit, the damping circuit includes a switch unit and a first resistor, the output end of the second drive circuit is connected to the control end of the switch unit, when the switch unit is turned on, the first resistor is connected between the first connection end and the second connection end, and when the switch unit is turned off, the first resistor is disconnected from the first connection end and the second connection end.

[0011] Preferably, the input end of the second drive circuit is connected to the first connection end, the second connection end and the output end of the first drive circuit, the output end of the first drive circuit is connected to the gate of the synchronous rectifier, and the damping circuit includes: a switch unit and a first resistor, the output end of the second drive circuit is connected to the control end of the switch unit, when the switch unit is turned on, the first resistor is connected between the first connection end and the second connection end, and when the switch unit is turned off, the first resistor is disconnected from the first connection end and the second connection end.

[0012] Preferably, the second driving circuit includes an RS trigger, a set terminal and a reset terminal of the RS trigger receive the driving signal, and an output signal of the RS trigger controls the connection and disconnection of the damping circuit with the first connection terminal and the second connection terminal.

[0013] Preferably, the second driving circuit includes: an RS trigger, a comparator, and an AND gate, the set terminal and the reset terminal of the RS trigger receive the driving signal, the output terminal of the RS trigger is connected to the first input terminal of the AND gate, the non-phase input terminal of the comparator is connected to the first connection terminal, the inverting input terminal of the comparator is connected to the second connection terminal, the output terminal of the comparator is connected to the second input terminal of the AND gate, and the output signal of the AND gate controls the connection and disconnection of the damping circuit with the first connection terminal and the second connection terminal.

[0014] Preferably, the switching unit includes a first switching tube, a second switching tube, and a third switching tube, the drain of the first switching tube is connected to the gates of the second switching tube and the third switching tube, the source of the first switching tube is grounded, the drain of the second switching tube is connected to the first connection end, the source of the second switching tube is connected to the source of the third switching tube, the drain of the third switching tube is connected to the first resistor and the second connection end in sequence, and the gate of the first switching tube is connected to the output end of the second driving circuit.

[0015] Furthermore, the magnitude of the first resistor controls the resonance attenuation amplitude of the flyback converter.

[0016] Furthermore, the first driving circuit, the second driving circuit and the switch unit are integrated in one chip.

[0017] Furthermore, the first resistor is integrated inside the chip or arranged outside the chip.

[0018] A flyback converter comprises a synchronous rectifier tube, and in particular, also comprises the synchronous rectifier controller.

[0019] The synchronous rectifier controller proposed in the utility model is integrated with a damping circuit, which is used to attenuate oscillation and reduce resonance amplitude when both the main power tube and the synchronous rectifier tube are turned off, thereby improving the EMC characteristics of the flyback converter. The synchronous rectifier controller shares the same drive signal to simultaneously control the on and off of the synchronous rectifier tube and whether the damping circuit is connected to both ends of the secondary winding of the flyback converter, which greatly simplifies the control logic and structural setting of the synchronous rectifier controller. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a working waveform diagram of a flyback converter in a DCM mode in the prior art;

[0021] Figure 2 This is a working waveform diagram of the flyback converter in the DCM mode in the first embodiment of the utility model;

[0022] Figure 3 This is a working waveform diagram of the flyback converter in the DCM mode in the second embodiment of the present utility model;

[0023] Figure 4 This is a structural diagram of the synchronous rectification controller proposed by the utility model applied in a flyback converter (the first resistor is built-in);

[0024] Figure 5 This is a structural diagram of the synchronous rectification controller proposed by the utility model applied in a flyback converter (the first resistor is external);

[0025] Figure 6is a structural diagram of the second driving circuit in the first embodiment;

[0026] Figure 7 is a structural diagram of a second driving circuit in the second embodiment;

[0027] Figure 8 This is the structural diagram of the switch unit. DETAILED DESCRIPTION

[0028] In the prior art, Figure 1 As shown in the figure, in the DCM mode (discontinuous mode) of the flyback converter, the LC oscillation circuit composed of parasitic capacitance and coil will produce harmonic oscillation when the main switch tube and the synchronous rectifier tube are turned off at the same time, which will lead to poor EMC characteristics of the ZVS flyback converter. And as the depth of the DCM mode increases, the number of resonant cycles in each switching cycle increases, and the periodic amplitude of this resonance increases after Fourier decomposition, so that the fundamental frequency and multiplier amplitude of this resonance will be high during the conduction test, and the EMC characteristics of the flyback converter will become worse.

[0029] In order to solve the above problems, the utility model proposes a synchronous rectification controller, wherein the synchronous rectification controller includes a first driving circuit, the driving signal generated by the first driving circuit is used to control the on and off of the synchronous rectifier tube in the flyback converter, and the synchronous rectifier tube will be turned on twice at intervals in each switching cycle, the synchronous rectifier tube is turned on once to perform freewheeling, and the secondary conduction of the synchronous rectifier tube enables the main power tube to achieve zero voltage switching in the next switching cycle; in particular,

[0030] The synchronous rectification controller further includes a damping circuit, a second driving circuit, a first connection terminal and a second connection terminal, wherein the first connection terminal is connected to the drain of the synchronous rectification tube, and the second connection terminal is connected to the output terminal of the flyback converter. The control method includes:

[0031] In each switching cycle, the second driving circuit controls the damping circuit to be connected between the first connection terminal and the second connection terminal at the end of the freewheeling of the synchronous rectifier according to the driving signal, and controls the damping circuit to be disconnected at the beginning of the secondary conduction of the synchronous rectifier.

[0032] Therefore, if Figure 2 As shown, in DCM mode, when the main power tube and the synchronous rectifier tube are turned off at the same time, the damping circuit will always be connected to both ends of the secondary winding, thereby attenuating the resonance, reducing the resonance amplitude, and improving the EMC characteristics of the flyback converter.

[0033] It can be seen that the synchronous rectifier controller proposed by the utility model is integrated with a damping circuit, which is used to attenuate oscillation and reduce resonance amplitude when both the main power tube and the synchronous rectifier tube are turned off, thereby improving the EMC characteristics of the flyback converter. Among them, the synchronous rectifier controller shares the same drive signal to simultaneously control the on and off of the synchronous rectifier tube and whether the damping circuit is connected to both ends of the secondary winding of the flyback converter, which greatly simplifies the control logic and structural setting of the synchronous rectifier controller.

[0034] Furthermore, in order to control the damping circuit to consume only the energy that causes resonance without causing unnecessary energy consumption, the utility model proposes that during the entire time period from the end of the freewheeling of the synchronous rectifier to the start of the secondary conduction of the synchronous rectifier, the damping circuit is not always controlled to be connected between the first connection end and the second connection end, but the damping circuit is controlled to be connected between the first connection end and the second connection end when the voltage of the first connection end is greater than the voltage of the second connection end during the time period. That is, on the basis of the control scheme of controlling the damping circuit to be connected between the first connection end and the second connection end at the end of the freewheeling of the synchronous rectifier and disconnecting the connection between the damping circuit and the first connection end and the second connection end at the start of the secondary conduction of the synchronous rectifier, the damping circuit is further controlled to be disconnected when the voltage of the second connection end is greater than or equal to the voltage of the first connection end.

[0035] Therefore, if Figure 3 As shown, in the process of damping resonance of the damping circuit, when the output voltage resonating to the flyback converter is greater than the drain voltage of the synchronous rectifier, the damping circuit is disconnected from the first connection end and the second connection end, so that the damping circuit will not consume the energy stored in the output capacitor of the flyback converter during the resonance process, thereby avoiding unnecessary energy loss.

[0036] Specifically, Figure 4 and Figure 5As shown, in the first embodiment, the first drive circuit in the synchronous rectification controller generates the first drive signal and the second drive signal to control the synchronous rectifier M2 of the flyback converter to turn on twice in each switching cycle, the first drive signal drives the synchronous rectifier M2 to turn on once for freewheeling, and the second drive signal drives the synchronous rectifier M2 to turn on twice to achieve zero voltage turn-on of the main power tube M1 in the next switching cycle. The synchronous rectification controller includes a damping circuit, a second drive circuit, a first connection terminal SW and a second connection terminal VO, the first connection terminal SW is connected to the drain of the synchronous rectifier M2, and the second connection terminal VO is connected to the output terminal of the flyback converter (that is, connected to the positive electrode of the output capacitor C0). In each switching cycle, the second drive circuit controls the damping circuit to be connected between the first connection terminal SW and the second connection terminal VO at the end time of the freewheeling of the synchronous rectifier M2 according to the first drive signal and the second drive signal, and controls the damping circuit to be disconnected from the first connection terminal SW and the second connection terminal VO at the start time of the secondary conduction of the synchronous rectifier M2.

[0037] Therefore, if Figure 2 As shown, in the DCM mode, when the main power tube M1 and the synchronous rectifier tube M2 are turned off at the same time, the damping circuit will always be connected to both ends of the secondary winding, so that the resonance is attenuated, the resonance amplitude is reduced, and the EMC characteristics of the flyback converter are improved.

[0038] Furthermore, the input end of the second driving circuit is connected to the output end of the first driving circuit, the output end of the first driving circuit is connected to the gate of the synchronous rectifier, the damping circuit includes a switch unit and a first resistor, and the output end of the second driving circuit is connected to the control end of the switch unit. When the second driving unit controls the switch unit to turn on according to the first driving signal and the second driving signal, the first resistor is connected between the first connection end and the second connection end; when the second driving unit controls the switch unit to turn off according to the first driving signal and the second driving signal, the first resistor is disconnected from the first connection end and the second connection end. Specifically, Figure 6 and Figure 8As shown, the second driving circuit includes an RS trigger, and the switch unit includes a first switch tube Q1, a second switch tube Q2, and a third switch tube Q3. Among them, the set end of the RS trigger receives the first driving signal, the reset end of the RS trigger receives the second driving signal, the output end of the RS trigger is connected to the gate of the first switch tube Q1, the source of the first switch tube Q1 is grounded, and the drain is connected to the gates of the second switch tube Q2 and the third switch tube Q3, the drain of the second switch tube Q2 is connected to the first connection end, the source of the second switch tube Q2 is connected to the source of the third switch tube Q3, the source of the third switch tube Q3 is connected to one end of the first resistor R1, and the other end of the first resistor R1 is connected to the second connection end VO. It can be seen that when the set end of the RS trigger receives the falling edge of the first drive signal and the reset end receives the rising edge of the second drive signal, the output end of the RS trigger outputs a high-level signal to drive the first switch tube Q3 to turn on. After the first switch tube Q3 is turned on, it drives the second switch tube Q2 and the third switch tube Q3 to turn on. Therefore, the first resistor R1 is connected between the first connection terminal SW and the second connection terminal VO to attenuate the resonance, reduce the resonance amplitude, and improve the EMC characteristics of the flyback converter. Figure 1 and Figure 2 It can be seen that the synchronous rectification controller introduces the first resistor R1 to attenuate the resonance during the system resonance period, thereby reducing the resonance amplitude.

[0039] In summary, the synchronous rectifier controller proposed in the utility model integrates a damping circuit, which is used to attenuate oscillation and reduce resonance amplitude when both the main power tube and the synchronous rectifier tube are turned off, thereby improving the EMC characteristics of the flyback converter. Among them, the synchronous rectifier controller shares the same drive signal to simultaneously control the on and off of the synchronous rectifier tube and whether the damping circuit is connected to both ends of the secondary winding of the flyback converter, which greatly simplifies the control logic and structural setting of the synchronous rectifier controller.

[0040] In the second embodiment, in order to control the damping circuit to consume only the energy causing resonance without causing unnecessary energy consumption, the second driving circuit controls the damping circuit in each switching cycle according to the first driving signal, the second driving signal, the voltage of the first connection terminal SW and the voltage of the second connection terminal VO. The damping circuit is connected between the first connection terminal SW and the second connection terminal VO during the first time period and when the voltage of the first connection terminal is greater than the voltage of the second connection terminal. The end time of the freewheeling of the synchronous rectifier tube M2 is the starting point of the first time period, and the start time of the secondary conduction of the synchronous rectifier tube M2 is the end point of the first time period.

[0041] Therefore, during the entire time period from the end of the freewheeling of the synchronous rectifier to the start of the secondary conduction of the synchronous rectifier, the damping circuit is not always connected between the first connection terminal SW and the second connection terminal VO, but when the voltage of the first connection terminal SW is greater than the voltage of the second connection terminal VO during this time period, the damping circuit is controlled to be connected between the first connection terminal SW and the second connection terminal VO. Figure 3 As shown, in the process of damping resonance of the damping circuit, when the output voltage from the resonance to the flyback converter is greater than the drain voltage of the synchronous rectifier, the damping circuit is disconnected from the first connection end and the second connection end, so that the damping circuit will not consume the energy stored in the output capacitor C0 during the resonance process, thereby avoiding unnecessary energy loss.

[0042] The input end of the second driving circuit is connected to the first connection end, the second connection end, and the output end of the first driving circuit; the output end of the first driving circuit is connected to the gate of the synchronous rectifier, the damping circuit includes a switch unit and a first resistor; the output end of the second driving circuit is connected to the control end of the switch unit. When the second driving circuit controls the switch unit to turn on according to the first driving signal, the second driving signal, the voltage of the first connection end, and the voltage of the second connection end, the first resistor is connected between the first connection end and the second connection end; when the second driving circuit controls the switch unit to turn off according to the first driving signal, the second driving signal, the voltage of the first connection end, and the voltage of the second connection end, the first resistor is disconnected from the first connection end and the second connection end. Specifically, as Figure 7 and Figure 8As shown, the second driving circuit includes an RS trigger, a comparator D1 and an AND gate U1, and the switch unit includes a first switch tube Q1, a second switch tube Q2, and a third switch tube Q3. Specifically, the set end of the RS trigger receives the first driving signal, the reset end of the RS trigger receives the second driving signal, the output end of the RS trigger is connected to the first input end of the AND gate U1, the positive input end of the comparator D1 is connected to the first connection end SW, the negative input end of the comparator D1 is connected to the second connection end VO, the output end of the comparator D1 is connected to the second input end of the AND gate U1, the output end of the AND gate U1 is connected to the gate of the first switch tube Q1, the source of the first switch tube Q1 is grounded, the drain is connected to the gates of the second switch tube Q2 and the third switch tube Q3, the drain of the second switch tube Q2 is connected to the first connection end, the source of the second switch tube Q2 is connected to the source of the third switch tube Q3, the source of the third switch tube Q3 is connected to one end of the first resistor R1, and the other end of the first resistor R1 is connected to the second connection end VO. It can be seen that when the set end of the RS trigger receives the falling edge of the first drive signal and the reset end receives the rising edge of the second drive signal, the output end of the RS trigger outputs a high-level signal. When the voltage of the first connection end SW is greater than the voltage of the second connection end VO, the comparator D1 outputs a high-level signal. At this time, the AND gate U1 outputs a high-level signal to drive the first switch tube Q3 to turn on. After the first switch tube Q3 is turned on, it drives the second switch tube Q2 and the third switch tube Q3 to turn on. Therefore, the first resistor R1 is connected between the first connection end SW and the second connection end VO to attenuate the resonance, reduce the resonance amplitude, and improve the EMC characteristics of the flyback converter. Figure 1 and Figure 3 It can be known that during the system resonance period and when the voltage at the first connection terminal SW is greater than the voltage at the second connection terminal VO, the synchronous rectification controller introduces the first resistor R1 to attenuate the resonance, thereby reducing the resonance amplitude.

[0043] In the first and second embodiments, the damping circuit proposed by the present invention is not simply composed of two series-connected switch tubes and a resistor, but by arranging two back-to-back switch tubes to prevent the parasitic diode of the switch tube from connecting the damping circuit between the first connection terminal SW and the second connection terminal VO when the switch tube is disconnected (that is, when the damping circuit is disconnected from the first connection terminal SW and the second connection terminal VO), thereby generating unnecessary energy loss. Figure 4 and Figure 5As shown, the first drive circuit, the second drive circuit and the switch unit are integrated inside a chip, and the first resistor R1 can be integrated inside the chip or outside the chip. By integrating the first drive circuit, the second drive circuit and the switch unit into one chip, the synchronous rectification controller can share the same drive signal and control the on and off of the synchronous rectifier tube and the connection of the damping circuit at the same time, which greatly simplifies the control logic and circuit structure setting of the synchronous rectification controller. In high-power applications, setting the first resistor outside the chip can not only prevent the chip from bearing a large current, but also reduce the surface of the chip. At the same time, the size of the first resistor controls the amplitude of the resonance attenuation. Setting the first resistor outside the chip also facilitates the adjustment of the resistance value, thereby adjusting the amplitude of the resonance attenuation.

[0044] In addition, it should be noted that how the first drive circuit in the synchronous rectifier generates the first drive signal and the second drive signal to drive the synchronous rectifier to conduct twice in each switching cycle is common knowledge in the art and will not be elaborated here. At the same time, in this embodiment, the first drive circuit generates two drive signals to drive the synchronous rectifier to conduct twice through two sets of logic, and the corresponding second drive circuit is also set in this case. Figure 2 and Figure 3 In the waveform diagram, the first drive signal and the second drive signal are simplified as one and are shown in the figure. However, in other embodiments, the first drive circuit can also generate a drive signal (with two pulse rising edges in one switching cycle) to drive the synchronous rectifier to conduct twice.

[0045] The utility model also proposes a flyback converter, which includes the synchronous rectification controller proposed above, and the synchronous rectification controller controls the damping circuit to be connected between the first connection end and the second connection end at the end time of the freewheeling of the synchronous rectifier tube, and controls the damping circuit to be disconnected from the first connection end and the second connection end at the beginning time of the secondary conduction of the synchronous rectifier tube, so as to attenuate the resonance amplitude and improve the EMC characteristics of the flyback converter.

[0046] Alternatively, the synchronous rectifier controller controls the damping circuit to be connected between the first connection terminal and the second connection terminal during the first time period and when the voltage at the first connection terminal is greater than the voltage at the second connection terminal, so as to attenuate the resonance amplitude and improve the EMC characteristics of the flyback converter. The end time of the freewheeling of the synchronous rectifier is the starting point of the first time period, and the start time of the secondary conduction of the synchronous rectifier is the end point of the first time period.

Claims

1. A synchronous rectifier controller, comprising a first drive circuit, wherein the first drive circuit generates a drive signal to control a synchronous rectifier tube in a flyback converter to be turned on twice in each switching cycle, wherein the synchronous rectifier tube is turned on once for freewheeling, and the synchronous rectifier tube is turned on twice to achieve zero voltage turn-on of a primary main power tube in the next switching cycle, wherein: The synchronous rectification controller includes a damping circuit, a second driving circuit, a first connection end and a second connection end, wherein the first connection end is connected to the drain of the synchronous rectifier tube, and the second connection end is connected to the output end of the flyback converter. In each switching cycle, the second drive circuit controls the damping circuit to be connected between the first connection end and the second connection end at the end of the freewheeling of the synchronous rectifier according to the drive signal, and controls the damping circuit to be disconnected from the first connection end and the second connection end at the start of the secondary conduction of the synchronous rectifier.

2. The synchronous rectification controller according to claim 1, characterized in that: In each switching cycle, the second drive circuit controls the damping circuit to be connected between the first connection end and the second connection end within the first time period and when the voltage of the first connection end is greater than the voltage of the second connection end according to the drive signal, the voltage of the first connection end and the voltage of the second connection end, wherein the end time of the freewheeling of the synchronous rectifier is the starting point of the first time period, and the start time of the secondary conduction of the synchronous rectifier is the end point of the first time period.

3. The synchronous rectification controller according to claim 1, characterized in that: The output end of the first drive circuit is connected to the gate of the synchronous rectifier and the input end of the second drive circuit, the damping circuit includes a switch unit and a first resistor, the output end of the second drive circuit is connected to the control end of the switch unit, when the switch unit is turned on, the first resistor is connected between the first connection end and the second connection end, when the switch unit is turned off, the first resistor is disconnected from the first connection end and the second connection end.

4. The synchronous rectification controller according to claim 2, characterized in that: The input end of the second driving circuit is connected to the first connection end, the second connection end and the output end of the first driving circuit, the output end of the first driving circuit is connected to the gate of the synchronous rectifier, and the damping circuit includes: a switching unit and a first resistor, the output end of the second driving circuit is connected to the control end of the switching unit, when the switching unit is turned on, the first resistor is connected between the first connection end and the second connection end, and when the switching unit is turned off, the first resistor is disconnected from the first connection end and the second connection end.

5. The synchronous rectification controller according to claim 1 or 3, characterized in that: The second driving circuit includes an RS trigger, a set terminal and a reset terminal of the RS trigger receive the driving signal, and an output signal of the RS trigger controls the connection and disconnection of the damping circuit with the first connection terminal and the second connection terminal.

6. The synchronous rectification controller according to claim 2 or 4, characterized in that: The second driving circuit includes: an RS trigger, a comparator, and an AND gate, wherein the set terminal and the reset terminal of the RS trigger receive the driving signal, the output terminal of the RS trigger is connected to the first input terminal of the AND gate, the non-phase input terminal of the comparator is connected to the first connection terminal, the inverting input terminal of the comparator is connected to the second connection terminal, the output terminal of the comparator is connected to the second input terminal of the AND gate, and the output signal of the AND gate controls the connection and disconnection of the damping circuit with the first connection terminal and the second connection terminal.

7. The synchronous rectification controller according to claim 3 or 4, characterized in that: The switch unit includes a first switch tube, a second switch tube, and a third switch tube. The drain of the first switch tube is connected to the gates of the second switch tube and the third switch tube, and the source of the first switch tube is grounded. The drain of the second switch tube is connected to the first connection end, the source of the second switch tube is connected to the source of the third switch tube, the drain of the third switch tube is connected to the first resistor and the second connection end in sequence, and the gate of the first switch tube is connected to the output end of the second drive circuit.

8. The synchronous rectification controller according to claim 3 or 4, characterized in that: The magnitude of the first resistor controls the resonance attenuation amplitude of the flyback converter.

9. The synchronous rectification controller according to claim 3 or 4, characterized in that: The first driving circuit, the second driving circuit and the switch unit are integrated in one chip.

10. The synchronous rectification controller according to claim 9, characterized in that: The first resistor is integrated inside the chip or arranged outside the chip.

11. A flyback converter, comprising a synchronous rectifier tube, characterized in that: It also includes the synchronous rectification controller as described in any one of claims 1 to 10.

Images