Quasi-resonance power supply sampling circuit

Abstract

The utility model provides a quasi-resonance power supply sampling circuit. The quasi-resonant power supply sampling circuit comprises a quasi-resonant power supply, an mos tube, a ZCD sampling circuit, a sampling diode, a tap and a transformer. The quasi-resonant power supply is connected with an input winding of the transformer through an mos tube; the quasi-resonant power supply is connected with an output winding of the transformer through the ZCD sampling circuit; and the tap is connected with the ZCD sampling circuit and is used for adjusting the backward voltage of a sampling diode on the sampling circuit. According to the quasi-resonant power supply sampling circuit provided by the invention, the output voltage of the transformer can be adjusted by using the tap, so that the reverse voltage of the sampling diode on the ZCD sampling circuit is reduced.

Description

Technical Field

[0001] This application belongs to the field of power conversion technology and relates to a quasi-resonant power sampling circuit. Background Technology

[0002] DC / AC or DC / DC power converters are widely used in industrial and residential applications such as photovoltaics, inverters, and home appliances, primarily to power electrical equipment. As industries place higher demands on product size, sealing, and cost control, the selection of diodes becomes difficult and costly, particularly in photovoltaics, where high voltage handling in inverters presents challenges. Therefore, finding a solution that enables quasi-resonant power sampling circuits to meet the requirements of low switching losses, low cost, and small size is a pressing issue. Utility Model Content

[0003] This application provides a quasi-resonant power supply sampling circuit for reducing the reverse voltage of the sampling diode.

[0004] In a first aspect, this application provides a quasi-resonant power supply sampling circuit, the quasi-resonant power supply sampling circuit comprising: a quasi-resonant power supply, a MOSFET, a ZCD sampling circuit, a sampling diode, a tap, and a transformer; the quasi-resonant power supply is connected to the input winding of the transformer via the MOSFET; the quasi-resonant power supply is connected to the output winding of the transformer via the ZCD sampling circuit; the tap is connected to the ZCD sampling circuit and is used to adjust the reverse voltage of the sampling diode on the sampling circuit.

[0005] In one implementation of the first aspect, the ZCD sampling circuit is connected to the transformer and is used to control the turn-on time of the MOSFET.

[0006] In one implementation of the first aspect, the quasi-resonant power supply is connected to the MOSFET and is used to send a drive signal to the MOSFET to control the MOSFET's turn-on and turn-off.

[0007] In one implementation of the first aspect, the quasi-resonant power supply is connected to the gate of the MOSFET, the drain of the MOSFET is grounded, and the source of the MOSFET is connected to the input winding of the transformer.

[0008] In one implementation of the first aspect, the output winding includes a first output winding, a second output winding, a third output winding, and an auxiliary winding; the auxiliary winding is connected to the ZCD sampling circuit via the tap.

[0009] In one implementation of the first aspect, the ZCD sampling circuit includes an OPL resistor, an OPU resistor, and a ZCD resistor; the first terminal of the OPL resistor is grounded, and the second terminal of the OPL resistor is connected to the quasi-resonant power supply and the first terminal of the OPU resistor, respectively; the second terminal of the OPU resistor is connected to the first terminal of the ZCD resistor, and the second terminal of the ZCD resistor is connected to the tap.

[0010] In one implementation of the first aspect, the positive terminal of the sampling diode is connected to the second terminal of the OPU resistor, and the negative terminal of the sampling diode is connected to the first terminal of the OPU resistor.

[0011] In one implementation of the first aspect, the quasi-resonant power supply sampling circuit further includes diodes, the diodes including a first diode, a second diode, and a third diode; the first diode is disposed on the first output winding; the second diode is disposed on the second output winding; and the third diode is disposed on the third output winding.

[0012] In one implementation of the first aspect, the quasi-resonant power supply sampling circuit further includes capacitors, including a first capacitor, a second capacitor, and a third capacitor; the first capacitor is disposed at both ends of the first output winding; the second capacitor is disposed at both ends of the second output winding; and the third capacitor is disposed at both ends of the third output winding.

[0013] In one implementation of the first aspect, the tap is disposed on the auxiliary winding for adjusting the output voltage of the auxiliary winding.

[0014] As described above, the quasi-resonant power supply sampling circuit of this application has the following beneficial effects:

[0015] The voltage output from the transformer to the ZCD sampling circuit can be adjusted by using the taps on the transformer, which reduces the reverse withstand voltage of the sampling diode in the ZCD sampling circuit. Attached Figure Description

[0016] Figure 1 The diagram shown is a schematic representation of the quasi-resonant power supply sampling circuit described in an embodiment of this application.

[0017] Figure 2 The diagram shown is a structural schematic of the transformer described in an embodiment of this application.

[0018] Figure 3 The diagram shown is a structural schematic of the transformer described in an embodiment of this application.

[0019] Figure 4 The diagram shown is a structural schematic of the transformer described in an embodiment of this application.

[0020] Figure 5 The diagram shown is a schematic representation of the ZCD sampling circuit described in an embodiment of this application.

[0021] Figure 6 The diagram shown is a schematic representation of the quasi-resonant power supply sampling circuit described in an embodiment of this application.

[0022] Component designation explanation

[0023] 1 Quasi-resonant power supply sampling circuit

[0024] 11 Quasi-resonant power supply

[0025] 12 Transformers

[0026] 121 Input winding

[0027] 122 First output winding

[0028] 123 Second output winding

[0029] 124 Third output winding

[0030] 125 Auxiliary winding

[0031] 13 taps

[0032] 14 ZCD sampling circuit

[0033] Q1 MOS tube

[0034] D1 sampling diode

[0035] D01 First Diode

[0036] D02 Second Diode

[0037] D03 Third Diode

[0038] C01 First Capacitor

[0039] C02 Second Capacitor

[0040] C03 Third Capacitor

[0041] R ZCD ZCD resistor

[0042] R opu OPU resistors

[0043] R opL OPL resistors Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, unless otherwise specified, the following embodiments and features in the embodiments can be combined with each other.

[0046] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0047] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0048] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0049] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0050] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. Therefore, the drawings only show the components related to this application and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0051] DC / AC or DC / DC power converters are widely used in industrial and residential applications such as photovoltaics, inverters, and home appliances, primarily to power electrical equipment. With increasing industry demands for smaller size, better sealing, and stricter cost control, low switching losses, low cost, and small size are becoming increasingly important requirements for power converters.

[0052] As a high-efficiency power converter, the quasi-resonant power supply detects the oscillation voltage of the MOSFET and turns on the MOSFET during the voltage trough, thus charging and discharging the primary winding of the transformer. The primary winding of the transformer will then be induced with voltage. The quasi-resonant converter needs to detect the voltage, and generally an auxiliary winding of the transformer is added. By detecting the voltage of the output auxiliary winding, ZCD trough detection is performed to reduce the turn-on loss of the MOSFET.

[0053] When the DC bus voltage input to the platform is 600V or higher, the following problems occur in the system:

[0054] 1) The reverse withstand voltage of the diode in the auxiliary winding ZCD sampling circuit is too high. 2) Difficulty in selecting high reverse withstand voltage diodes. 3) Selecting components based on the circuit's reverse voltage is too costly, and the components that meet the requirements are too large, and the diodes have poor reverse recovery characteristics.

[0055] The following embodiments of this application provide a quasi-resonant power supply sampling circuit to regulate the reverse voltage of the diodes on the ZCD sampling circuit.

[0056] The principle and implementation of a quasi-resonant power supply sampling circuit of this embodiment will be described in detail below with reference to the accompanying drawings, so that those skilled in the art can understand the quasi-resonant power supply sampling circuit of this embodiment without creative effort.

[0057] like Figure 1 As shown, this embodiment provides a quasi-resonant power supply sampling circuit. The quasi-resonant power supply sampling circuit 1 includes: a quasi-resonant power supply 11, a MOSFET Q1, a ZCD sampling circuit 14, a sampling diode D1, a tap 13, and a transformer 12. The quasi-resonant power supply 11 is connected to the input winding of the transformer 12 via the MOSFET Q1. The quasi-resonant power supply 11 is connected to the output winding of the transformer 12 via the ZCD sampling circuit 14. The tap 13 is connected to the ZCD sampling circuit 14 and is used to adjust the reverse voltage of the sampling diode on the sampling circuit. The ZCD sampling circuit 14 is connected to the transformer 12 via the tap 13 and is used to control the turn-on time of the MOSFET.

[0058] Specifically, the ZCD (Zero Crossing Detection) sampling circuit can control the switching on and off of the MOSFET to achieve quasi-resonant switching. The ZCD sampling current can detect the oscillation waveform of the MOSFET and identify the trough moment of the oscillation waveform. When the oscillation waveform drops to the trough moment, the ZCD sampling circuit can send a drive signal to control the MOSFET to turn on.

[0059] As can be seen from the above description, the quasi-resonant power supply sampling circuit provided in this application controls the turn-on time of the MOSFET through the ZCD sampling circuit, and adjusts the reverse voltage of the diode on the ZCD sampling circuit through the taps connected to the ZCD sampling circuit.

[0060] In one embodiment of this application, the quasi-resonant power supply is connected to the MOSFET. When the quasi-resonant power supply is working, a drive signal is sent through the MOSFET to control the MOSFET's on and off states. The quasi-resonant power supply is connected to the gate of the MOSFET, the drain of the MOSFET is grounded, and the source of the MOSFET is connected to the input winding of the transformer.

[0061] For example, when MOSFET Q1 is turned off, the output winding of the transformer outputs a voltage. When the energy of the transformer core is completely released, the junction capacitance of the transformer's input winding and MOSFET Q1 resonates. The ZCD sampling circuit detects the oscillation waveform of MOSFET Q1. At this time, the quasi-resonant power supply outputs V through the detection of the ZCD sampling voltage. ZCD The waveform is used to detect the trough of the MOSFET in order to obtain the turn-on time of MOSFET Q1.

[0062] Specifically, when the quasi-resonant power supply sends a turn-off signal to MOSFET Q1, MOSFET Q1 turns off, preventing current flow and causing a sharp drop in the primary winding current of the transformer. Due to the mutual inductance between the primary winding and the core, the energy stored in the core is released when the current decreases, resulting in a reverse electromotive force across the primary winding. An LC resonance exists between the junction capacitance of MOSFET Q1 and the primary winding of the transformer. When the core energy is fully released, the LC circuit begins to resonate, causing an oscillating waveform in the drain voltage of MOSFET Q1. The ZCD sampling circuit detects the oscillation waveform of MOSFET Q1. When the voltage drops to zero (i.e., a trough), the ZCD sampling circuit outputs a signal to the quasi-resonant power supply. After receiving the signal from the ZCD sampling circuit, the quasi-resonant power supply sends an turn-on signal to MOSFET Q1, turning it on during the trough to achieve quasi-resonant switching.

[0063] It should be noted that the resonant frequency depends on the parameters of the LC circuit, including the junction capacitance of MOSFET Q1 and the inductance of the primary winding of the transformer. The higher the resonant frequency, the higher the turn-on frequency of MOSFET Q1, and the higher the conversion efficiency of the resonant power supply.

[0064] Preferably, the quasi-resonant power supply switches the MOSFET Q1, and after the transformer winding coil undergoes charging and discharging, the output winding coil induces a voltage. When the MOSFET is turned on, the quasi-resonant power supply detects the oscillation voltage waveform of the MOSFET and turns on the MOSFET at the trough of the oscillation voltage, thereby reducing the switching loss of the MOSFET.

[0065] Please see Figure 2 The output windings of the transformer 12 include a first output winding 122, a second output winding 123, a third output winding 124, and an auxiliary winding 125. The first output winding 122 has N1 turns and a first output voltage of VOUT1; the second output winding 123 has N2 turns and a second output voltage of VOUT2; the third output winding 124 has N3 turns and a third output voltage of VOUT3; the auxiliary winding 125 has Naux turns and an output voltage of Vaux. The transformer input winding 121 has Np turns and an input voltage of V... inThe auxiliary winding 125 is connected to the ZCD sampling circuit 14 via the tap 13. The tap 13 is disposed on the auxiliary winding 125 and is used to adjust the output voltage of the auxiliary winding.

[0066] Please see Figure 3 The transformer further includes diodes, including a first diode D01, a second diode D02, and a third diode D03. The first diode D01 is disposed on the first output winding. The second diode D02 is disposed on the second output winding. The third diode D03 is disposed on the third output winding.

[0067] Specifically, the diode is used for output rectification. The AC voltage output by the transformer needs to be rectified into DC voltage before it can be supplied to the load. As a unidirectional conductive device, the diode has unidirectional conduction characteristics and rectification function. When the voltage direction of the transformer output winding is the same as the diode direction, the diode conducts, allowing current to flow. When the voltage direction is opposite to the diode direction, the diode is cut off, preventing current from flowing. Based on the unidirectional conduction characteristic of the diode, the AC voltage output by the transformer can be converted into a unidirectional pulsating DC voltage. In this embodiment, each of the three output windings of the transformer is connected to a diode to rectify the AC voltage output by the corresponding winding into DC voltage.

[0068] Please see Figure 4 The transformer further includes capacitors, including a first capacitor C01, a second capacitor C02, and a third capacitor C03. The first capacitor C01 is disposed across the two ends of the first output winding. The second capacitor C02 is disposed across the two ends of the second output winding. The third capacitor C03 is disposed across the two ends of the third output winding.

[0069] Specifically, the capacitor is used for voltage support. The pulsating DC voltage output after diode rectification still contains a certain AC component, i.e., ripple voltage. To improve the stability of the output voltage, a filter capacitor needs to be connected after the diode for voltage filtering and voltage support. Based on the characteristic of capacitors storing charge, when the voltage rises, the capacitor charges and stores energy. When the voltage drops, the capacitor discharges and releases energy. Through the charging and discharging process of the capacitor, voltage fluctuations can be smoothed, ripple voltage reduced, and the stability of the output voltage further improved. The capacitor can provide a large current in a short time, compensating for fluctuations in the load current and maintaining the stability of the output voltage. In this embodiment, a capacitor is connected to each end of the three output windings of the transformer to filter and support the DC voltage output from the windings.

[0070] By combining diodes and capacitors, the AC voltage output from a transformer can be converted into a stable and balanced DC voltage.

[0071] Specifically, the output voltage of the transformer's third output winding remains unchanged, while the output voltage of the auxiliary winding AUX decreases, reducing the reverse voltage at the MOSFET's turn-on moment and further reducing the reverse voltage of the sampling diode. When the MOSFET is turned off and generates an oscillating voltage, the auxiliary winding couples the MOSFET's oscillation waveform, and the voltage waveform of the MOSFET is acquired through the ZCD sampling circuit to control the MOSFET's turn-on moment.

[0072] Preferably, the auxiliary winding AUX is positioned at the middle of the third output winding VOUT3 by adding taps, and the number of turns in the auxiliary winding AUX is less than the number of turns in the third output winding VOUT3. Due to the reduced number of turns, the output voltage of the auxiliary winding AUX is lower than the output voltage of the third output winding VOUT3. When MOSFET Q1 is turned off, the junction capacitance of the transformer input winding and MOSFET Q1 resonates, generating an oscillating voltage. Because the output voltage of the auxiliary winding AUX is lower, the reverse voltage on the auxiliary winding AUX is also lower when MOSFET Q1 is turned on, thereby reducing the reverse withstand voltage of the diode in the ZCD sampling circuit. The auxiliary winding AUX couples the oscillation waveform of MOSFET Q1, transmitting the oscillation waveform to the ZCD sampling circuit. The ZCD sampling circuit detects the oscillation waveform of MOSFET Q1 and controls MOSFET Q1 to turn on at the trough of the oscillation voltage, thereby reducing the turn-on loss of the MOSFET and improving the power conversion efficiency. When MOSFET Q1 is turned on, the primary winding of the transformer charges and discharges the third output winding VOUT3, thereby outputting a DC voltage. The output voltage of the auxiliary winding AUX is used to reduce the reverse withstand voltage of the diodes in the ZCD sampling circuit.

[0073] Please see Figure 5 The ZCD sampling circuit includes an OPL resistor R. opl OPU resistor R opu and ZCD resistor R zcd The OPL resistor R opl The first terminal is grounded, and the OPL resistor R opl The second terminal is connected to the quasi-resonant power supply and the OPU resistor R, respectively. opu The first end is connected. The OPU resistor R opu The second terminal is connected to the ZCD resistor R zcd The first end is connected, the ZCD resistor R zcd The second terminal is connected to the tap. In one embodiment of this application, the positive terminal of the sampling diode is connected to the OPU resistor R. opu The second terminal is connected, and the negative terminal of the sampling diode is connected to the OPU resistor R. opu Connect the first end.

[0074] Preferably, when the MOSFET is turned off, and the Vds voltage of MOSFET Q1 drops to zero, the diode connected in parallel across the OPU resistor in the ZCD sampling circuit turns on. After the MOSFET is turned on at the trough of the MOSFET oscillation voltage, the sampling diode D1 connected to the auxiliary winding has a reverse voltage.

[0075] The ZCD resistor, OPU resistor, and OPL resistor satisfy the following relationship:

[0076]

[0077]

[0078] Among them, V OPP = -300mV, indicating that the minimum voltage that the quasi-resonant power supply can accept is 300mV, N p,aux The tap represents the turns ratio of the auxiliary winding and the third output winding. The tap adjusts the output voltage by changing the turns ratio of the transformer. Changing the turns ratio of the third output winding and the auxiliary winding by tapping reduces the output voltage of the auxiliary winding.

[0079] The taps can be connected to any position on the third output winding. By moving the taps, the number of turns in the auxiliary winding can be changed, thereby adjusting the output voltage of the auxiliary winding. Adjusting using taps offers high flexibility, allowing for various voltage adjustments to meet different quasi-resonant sampling requirements. Furthermore, the adjustment method is stable and not easily affected by external factors.

[0080] It should be noted that the number of taps can be set according to the output winding and the actual quasi-resonant sampling requirements.

[0081] Furthermore, the accuracy of the ZCD sampling circuit depends on the diode's forward voltage and the resistor's resistance. By changing the tap position, the output voltage can be adjusted more easily, thereby reducing the diode's forward voltage. Lowering the output voltage of the auxiliary winding by tapping reduces the reverse withstand voltage of the sampling diode in the ZCD sampling circuit, decreases its losses, and improves the power conversion efficiency.

[0082] Please see Figure 6The quasi-resonant power supply circuit provided in this application sends a drive signal (Driver) to MOSFET Q1 to turn it on. At this time, current flows through MOSFET Q1 to the input winding of the transformer, charging the input winding. A magnetic field is established in the transformer core, storing energy. Changes in the input winding current induce a voltage in the output winding. When the quasi-resonant power supply stops sending the drive signal to MOSFET Q1, the MOSFET turns off, and the energy in the transformer core is released through the junction capacitance of MOSFET Q1 and the output winding, generating an oscillating voltage. The auxiliary winding couples the oscillation waveform of MOSFET Q1 and transmits it to the ZCD sampling circuit. The ZCD sampling circuit detects the oscillation waveform of MOSFET Q1 and sends a ZCD signal at the trough of the oscillation voltage. After receiving the ZCD signal of the ZCD sampling current, the quasi-resonant power supply sends a drive signal to MOSFET Q1 again to turn it on. The turns ratio of the auxiliary winding to the third output winding can be adjusted by tapping. When the number of turns Naux of the auxiliary winding is less than the number of turns N3 of the third output winding, the output voltage Vaux of the auxiliary winding decreases. When the MOSFET Q1 is turned off, the reverse voltage generated on the auxiliary winding also decreases, thereby reducing the reverse withstand voltage of the sampling diode on the ZCD sampling circuit.

[0083] In summary, the quasi-resonant power supply sampling circuit provided in this application sends a drive signal to the MOSFET to control its switching. Taps are added to the output winding of the quasi-resonant power supply to form an auxiliary winding and an output winding. By adjusting the number of turns in the auxiliary winding, the reverse voltage of the sampling diode when the MOSFET is turned on is reduced, thus meeting the requirements of the ZCD sampling circuit. When the platform input voltage is too high, adjusting the taps to reduce the reverse voltage of the sampling diode solves the problems of difficult selection, high cost, and large size of high-voltage diodes. Simultaneously, it reduces the MOSFET's turn-on loss and improves the sampling accuracy of the ZCD sampling circuit.

[0084] The descriptions of the processes or structures corresponding to the above figures each have their own emphasis. For parts of a process or structure that are not described in detail, please refer to the relevant descriptions of other processes or structures.

[0085] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this application should still be covered by the claims of this application.

Claims

1. A quasi-resonant power supply sampling circuit, characterized in that, The quasi-resonant power supply sampling circuit includes: a quasi-resonant power supply, a MOSFET, a ZCD sampling circuit, a sampling diode, a tap, and a transformer; The quasi-resonant power supply is connected to the input winding of the transformer via a MOSFET; The quasi-resonant power supply is connected to the output winding of the transformer through the ZCD sampling circuit; The tap is connected to the ZCD sampling circuit and is used to adjust the reverse voltage of the sampling diode on the sampling circuit.

2. The quasi-resonant power supply sampling circuit according to claim 1, characterized in that, The ZCD sampling circuit is connected to the transformer and is used to control the turn-on time of the MOSFET.

3. The quasi-resonant power supply sampling circuit according to claim 1, characterized in that, The quasi-resonant power supply is connected to the MOSFET and is used to send a drive signal to the MOSFET to control the MOSFET's turn-on and turn-off.

4. The quasi-resonant power supply sampling circuit according to claim 1, characterized in that, The quasi-resonant power supply is connected to the gate of the MOSFET, the drain of the MOSFET is grounded, and the source of the MOSFET is connected to the input winding of the transformer.

5. The quasi-resonant power supply sampling circuit according to claim 1, characterized in that, The output winding includes a first output winding, a second output winding, a third output winding, and an auxiliary winding; the auxiliary winding is connected to the ZCD sampling circuit via the tap.

6. The quasi-resonant power supply sampling circuit according to claim 5, characterized in that, The quasi-resonant power supply sampling circuit also includes diodes, which include a first diode, a second diode, and a third diode; The first diode is disposed on the first output winding; The second diode is disposed on the second output winding; The third diode is disposed on the third output winding.

7. The quasi-resonant power supply sampling circuit according to claim 5, characterized in that, The quasi-resonant power supply sampling circuit also includes capacitors, including a first capacitor, a second capacitor, and a third capacitor; The first capacitor is disposed at both ends of the first output winding; The second capacitor is disposed at both ends of the second output winding; The third capacitor is located at both ends of the third output winding.

8. The quasi-resonant power supply sampling circuit according to claim 5, characterized in that, The tap is located on the auxiliary winding and is used to adjust the output voltage of the auxiliary winding.

9. The quasi-resonant power supply sampling circuit according to claim 1, characterized in that, The ZCD sampling circuit includes an OPL resistor, an OPU resistor, and a ZCD resistor; The first end of the OPL resistor is grounded, and the second end of the OPL resistor is connected to the quasi-resonant power supply and the first end of the OPU resistor, respectively; the second end of the OPU resistor is connected to the first end of the ZCD resistor, and the second end of the ZCD resistor is connected to the tap.

10. The quasi-resonant power supply sampling circuit according to claim 9, characterized in that, The positive terminal of the sampling diode is connected to the second terminal of the OPU resistor, and the negative terminal of the sampling diode is connected to the first terminal of the OPU resistor.

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