A dual-winding secondary feedback switching power supply

Abstract

The present disclosure discloses a dual-winding secondary-side feedback switching power supply, comprising: a primary-side rectifier and filter unit, a control unit, a self-power supply unit, a secondary-side feedback unit, an OVP unit, a dual-winding transformer, and a voltage signal acquisition unit. The present disclosure obtains a regulated output through secondary-side feedback, monitors the output voltage through overvoltage protection, and controls the output voltage within a safe range; on the other hand, the bootstrap power supply can effectively reduce the standby power consumption.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic circuits, and in particular relates to a dual-winding secondary-side feedback switching power supply. Background Art

[0002] Switching power supplies are power supply conversion devices for electronic equipment and electrical appliances. As people pay more and more attention to the safety of switching power supplies, the application of isolated switching power supplies is becoming more and more widespread.

[0003] Traditional isolated switching power supplies often use optocoupler isolation feedback to obtain stable voltage output, such as Figure 1 The system uses the optocoupler set in the feedback loop to output the voltage V out The signal is fed back to the PWM module in the switching power supply control chip, and the PWM module then adjusts the energy transferred from the transformer to the secondary side by controlling the duty cycle, thereby achieving a constant voltage output on the secondary side. The power required for the switching power supply control chip to execute the control process is provided by a self-powered circuit, which consists of a starting resistor R1, a power tube Q1, a diode D2, and an external charging capacitor C2. However, this technology has the following problems in practical applications: 1. When the feedback loop is disconnected, such as when the light-emitting diode in the optocoupler is broken down and short-circuited, the primary switching power supply control chip cannot monitor and control the output voltage V out , when the output voltage is too high, the load will be burned, or even a more serious safety accident will occur. 2. Considering the loss on R1, R1 is usually selected as a MΩ resistor. When Q1 supplies power to C2, it is in the amplification area and is not saturated. Therefore, the voltage drop is very high, even up to hundreds of volts, resulting in a large loss in power supply, making it difficult to achieve the sixth-level energy efficiency standard.

[0004] In summary, it is urgent to design a switching power supply system to improve the safety of the system and reduce the standby power consumption. Summary of the invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a dual-winding secondary-side feedback switching power supply, which obtains a regulated output through secondary-side feedback, and uses overvoltage protection to monitor the output voltage to prevent the output voltage from getting out of control and causing a safety accident.

[0006] In order to achieve the above objectives, the present disclosure describes the following technical solutions in detail:

[0007] A dual-winding secondary-side feedback switching power supply includes: a primary-side rectification and filtering unit, a control unit, a self-power supply unit, an overvoltage protection unit, a secondary-side feedback unit, a dual-winding transformer and a voltage signal acquisition unit; wherein:

[0008] The primary side rectifying and filtering unit includes a rectifying bridge and a C1 capacitor, which is used to convert alternating current into direct current for input;

[0009] The control unit includes a PWM module and a driving module, which are used to control the charging and discharging process of the self-powered unit and make corresponding adjustments to the circuit based on the received feedback information;

[0010] The self-power supply unit is connected to the power supply Vin and the control unit respectively, and is used for storing energy and supplying power to the control unit;

[0011] The secondary side feedback unit is provided with a feedback output terminal, one end of which is connected to the positive plate or negative plate of the energy storage capacitor of the self-powered unit, and the other end is connected to the PWM module, for detecting the change of the secondary side output signal and feeding back to the control unit;

[0012] One end of the OVP unit is connected to the voltage signal acquisition unit, and the other end is connected to the PWM module to detect the output voltage V out When the preset threshold is exceeded, an OVP signal is generated and output to the PWM module to put the power supply into overvoltage protection state;

[0013] The dual-winding transformer includes a primary inductor Lp and a secondary inductor Ls, wherein the positive electrode of Lp is connected to the switch tube of the self-power supply unit, and the negative electrode is grounded;

[0014] One end of the voltage signal acquisition unit is grounded, and the other end is connected to the positive electrode of the primary inductor Lp.

[0015] Preferably, the voltage signal acquisition unit includes resistors R8 and R9, and a common end of the resistors R8 and R9 is connected to the overvoltage protection unit.

[0016] Preferably, the secondary side feedback unit includes a voltage stabilizing device, an optocoupler and a feedback auxiliary device; the optocoupler includes a light emitting diode and a phototransistor, and the collector and emitter of the phototransistor are feedback output ends; wherein, the collector of the phototransistor is connected to the chip gnd, and the emitter is connected to the PWM module through the chip FB pin; the feedback auxiliary device includes a voltage dividing resistor.

[0017] Preferably, the self-power supply unit includes a starting resistor, a first switch tube, a second switch tube, a Vcc charging capacitor management module and a Vcc charging capacitor; wherein,

[0018] The Vcc charging capacitor is an energy storage capacitor of the self-powered unit;

[0019] The drain of the first switch tube is connected to the power supply V in The source electrode is connected to the drain electrode of the second switch tube;

[0020] and,

[0021] The common end of the first switch tube and the second switch tube is connected through V cc Charge management unit and V cc The charging capacitor is connected;

[0022] The gates of the first switch tube and the second switch tube are connected to the driving module of the control unit;

[0023] When the circuit is working normally, the first switch is turned on and the second switch is turned off, forming a power supply V in , a charging path from the first switch tube to the Vcc charging capacitor to achieve bootstrap power supply;

[0024] When the first and second switch tubes are turned off at the same time, resulting in insufficient power supply to the circuit, the first switch tube is turned on to achieve high voltage power supply.

[0025] Preferably, the bootstrap power supply is applicable to any of the following load circuits: no-load, light-load and heavy-load.

[0026] Preferably, the first switch tube and the second switch tube are voltage driven.

[0027] Preferably, the source of the second switch tube is connected to a sampling resistor, and the input end of the sampling resistor is connected to a control unit for monitoring the ILp current when the primary side is turned on. The control unit obtains and controls the current peak value of ILp in the primary circuit to achieve cycle-by-cycle overcurrent protection.

[0028] Preferably, the switching power supply also includes an undervoltage protection unit, the input end of the undervoltage protection unit is connected to the common end of resistors R8 and R9, and the output end is connected to the PWM module, and is used to generate an undervoltage signal and output it to the PWM module to put the power supply into an undervoltage protection state when it is detected that the power supply Vin is lower than a preset threshold.

[0029] Preferably, the switching power supply also includes an absorption unit, which includes a resistor R1, a capacitor C4 and a diode D1; wherein, after the resistor R1 and the capacitor C4 are connected in parallel, one end is connected to the positive electrode of the primary inductor Lp through the diode D1, and the other end is connected to the negative electrode of the primary inductor Lp.

[0030] Preferably, the switching power supply further comprises an output rectification and filtering unit for converting AC power into half-wave DC power and further filtering out AC components to reduce ripple before output.

[0031] Preferably, the rectification and filtering unit includes a diode and a capacitor.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The present invention designs a switching power supply circuit that uses secondary side feedback and overvoltage protection to jointly control the output voltage. On the one hand, the secondary side feedback is used to quickly respond to and adjust the output voltage to obtain a regulated output; on the other hand, the overvoltage protection is used to monitor the output voltage. When the output voltage exceeds a preset threshold, the overvoltage protection is activated to prevent the output voltage from being out of control when the optocoupler feedback loop fails, resulting in a safety accident.

[0034] 2. The present disclosure designs a floating ground structure, which facilitates accurate and convenient voltage data collection, helps to achieve accurate overvoltage protection control, and the voltage sampling circuit is simple, which simplifies the production process and reduces costs;

[0035] 3. The present disclosure also designs a self-powered circuit that realizes the switching power supply through a bootstrap method. During the bootstrap power supply process, since the switch tube is in a saturated conduction state, the dissipated power is extremely small, thereby reducing the standby power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the structure of a traditional switching power supply circuit;

[0037] Figure 2 A schematic diagram of the structure of a switching power supply circuit provided by the present disclosure;

[0038] Figure 3 A schematic diagram of the structure of another switching power supply circuit provided by the present disclosure;

[0039] Figure 4 This is a schematic diagram of the bootstrap power supply waveform when the circuit is overloaded;

[0040] Figure 5 This is a schematic diagram of the bootstrap power supply waveform when the circuit is unloaded or lightly loaded.

[0041] The symbols in the figure are:

[0042] 1-primary side rectification and filtering unit; 2-control unit; 3-Brown out unit; 4-voltage signal acquisition unit; 5-secondary side feedback unit (51-optical coupler; 52-feedback auxiliary device); 6-absorption unit; 7-output rectification and filtering unit; 8-OVP unit. DETAILED DESCRIPTION

[0043] The following will be combined with the attached embodiment of the present invention Figure 1 To Attachment Figure 5 , the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only 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 ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] The switch tube involved in the technical solution provided in the embodiment of the present invention may be a transistor such as MOS, MESFET, JFET, etc., and may be an enhancement type or a depletion type. The embodiments of the present invention are described using MOS tubes as examples; the connection involved in the technical solution may be a direct connection of components or an electrical connection.

[0045] The following is a detailed description of various embodiments of the present disclosure in conjunction with the accompanying drawings. It should be noted that the display order of the embodiments of the present disclosure only represents the order of the embodiments, and does not represent the advantages or disadvantages of the technical solutions provided by the embodiments.

[0046] like Figure 2 As shown, a dual-winding secondary feedback switching power supply circuit includes: a primary side rectification and filtering unit 1, a control unit 2, a self-power supply unit, a secondary side feedback unit 5, an OVP unit 8, a dual-winding transformer and a voltage signal acquisition unit 4; wherein,

[0047] The primary side rectification and filtering unit includes a rectifier bridge and a C1 capacitor, which is used to convert AC power into DC power Vin for input;

[0048] The control unit includes a PWM module and a driving module, which are used to control the charging and discharging process of the self-powered unit and make corresponding adjustments to the circuit based on the received feedback information;

[0049] The self-power supply unit is connected to the power supply Vin and the control unit respectively, and is used for storing energy and supplying power to the control unit;

[0050] The secondary side feedback unit is provided with a feedback output terminal, one end of which is connected to the positive plate or negative plate of the energy storage capacitor of the self-powered unit, and the other end is connected to the PWM module, for detecting the change of the secondary side output signal and feeding back to the control unit;

[0051] One end of the OVP unit is connected to the voltage signal acquisition unit, and the other end is connected to the PWM module to detect the output voltage V out When the preset threshold is exceeded, an OVP signal is generated and output to the PWM module to put the power supply into overvoltage protection state;

[0052] The dual-winding transformer includes a primary inductor Lp and a secondary inductor Ls, wherein the positive electrode of Lp is connected to the switch tube of the self-power supply unit, and the negative electrode is grounded;

[0053] One end of the voltage signal acquisition unit is grounded, and the other end is connected to the positive electrode of the primary inductor Lp.

[0054] The above-mentioned embodiments fully disclose the technical solution of the present invention. Compared with the problem in the prior art that the output voltage cannot be detected and the output cannot be controlled, resulting in excessive voltage and burning the load, the present invention, on the one hand, responds to and adjusts the output voltage through secondary side feedback to obtain a regulated output; on the other hand, it uses overvoltage protection to detect the output voltage and perform overvoltage protection to avoid safety accidents caused by excessive output voltage.

[0055] Furthermore, the present invention realizes self-power supply through a bootstrap method. During the power supply process, the switch tube is in a saturated conduction state, thereby overcoming the problem of large power supply loss in the prior art.

[0056] In another embodiment, the voltage signal acquisition unit includes resistors R8 and R9, and a common end of the resistors R8 and R9 is connected to the overvoltage protection unit.

[0057] In another embodiment, the secondary side feedback unit 5 includes a voltage stabilizing device, an optical coupler 51 and a feedback auxiliary device 52;

[0058] The optical coupler 51 includes a light emitting diode D3 and a phototransistor Q1, wherein the collector and emitter of the phototransistor Q1 are feedback output terminals; wherein the collector of the phototransistor Q1 is connected to the chip ground gnd, and the emitter is connected to the PWM module via the chip pin FB;

[0059] The feedback auxiliary device 52 includes voltage dividing resistors R3-R7.

[0060] In this embodiment, the output voltage Vout is divided by a voltage-dividing resistor and then input to the voltage stabilizing device for comparison with the reference voltage. The error voltage signal output by the operational amplifier controls the current flowing through the optocoupler 51. When the output voltage Vout is high, the current flowing through the optocoupler 51 increases, the voltage at the chip FB port decreases, and the PWM module controls the output duty cycle to decrease to reduce the energy transferred from the transformer to the secondary side, and the output voltage Vout begins to decrease; conversely, if the output voltage is lower than Vout, the PWM module controls the duty cycle to increase according to the feedback of the current of the optocoupler 51 to increase the energy transferred from the transformer to the secondary side, thereby increasing the output voltage Vout. In this way, the output voltage is continuously adjusted and controlled to stabilize at the set value.

[0061] In another embodiment, the self-power supply unit includes a starting resistor, a first switch tube M1, a second switch tube M2, a Vcc charging capacitor management module and a Vcc charging capacitor; wherein,

[0062] The Vcc charging capacitor is an energy storage capacitor of the self-powered unit;

[0063] The drain of the first switch tube M1 is connected to the power supply V in The source electrode is connected to the drain electrode of the second switch tube M2;

[0064] and,

[0065] The common terminal of the first switch tube M1 and the second switch tube M2 is connected through V cc Charging capacitor management module and V cc The charging capacitor is connected;

[0066] The gates of the first switch tube M1 and the second switch tube M2 are connected to the driving module of the control unit;

[0067] When the circuit is working normally, the first switch is turned on and the second switch is turned off, forming a power supply V in , a charging path from the first switch tube to the Vcc charging capacitor to achieve bootstrap power supply;

[0068] When the first and second switch tubes are turned off at the same time, resulting in insufficient power supply to the circuit, the first switch tube is turned on to achieve high voltage power supply.

[0069] In this embodiment, when the switching power supply is started, the power supply charges the gate-source parasitic capacitance Cgs of M1 through the starting resistor R1, raises the gate-source voltage Vgs of M1 to its threshold voltage Vth to turn on M1, forms a charging path from the power supply, M1 to the Vcc charging capacitor C2, charges Vcc to a preset value, and starts the control circuit. The Vcc charging capacitor management module is used to ensure the unidirectional conduction of the charging circuit, and protects the switch tube M1 by limiting the current of the charging circuit. In addition, the Vcc charging capacitor management module can also be provided with a Vcc voltage detection module, and the detected Vcc voltage is fed back to the control circuit.

[0070] Secondly, when the switching power supply control circuit works normally, the control circuit first drives M1 and M2 in the switching circuit to turn on at the same time, and then turns off M2 after a delay. At this time, the gate-source parasitic capacitance Cgs of M1 generates bootstrapping, and M1 maintains the on state, forming a charging path from the power supply, M1 to the charging capacitor C2, charging Vcc, and realizing bootstrap power supply; because M1 is in the bootstrap state at this time, the gate voltage is relatively large, M1 is in a saturated on state, and the voltage drop is extremely small, so the power consumption generated is extremely small.

[0071] After Vcc is charged, M2 is turned on again under the action of the control circuit, and the current flows from the input power supply through M1, M2, and the primary inductance Lp of the transformer into the ground, that is, the primary side is in the on state, and the transformer stores energy in this process; then M1 and M2 are turned off, and the primary side is cut off. Since the magnetic flux cannot change suddenly, the secondary side of the transformer induces a positive voltage at the top and a negative voltage at the bottom, and the energy is released through the secondary side.

[0072] In addition, when M1 and M2 are in the off state for a long time, resulting in insufficient Vcc power supply, the control circuit raises the gate voltage of M1 to Vcc. At the same time, the power supply charges the gate of M1 through the start-up resistor R1, turning on M1 and providing high-voltage power supply.

[0073] Regarding the bootstrap power supply of the circuit in the above embodiment, it should be particularly emphasized here that: unlike the prior art, the above embodiment is applicable to circuits with different load capabilities, including no-load, light-load and heavy-load.

[0074] For example, when the circuit is overloaded (the load impedance is small and the load current is large), the waveform is as follows: Figure 4 As shown. At this time, Vcc power supply adopts bootstrap power supply mode. When the primary side is turned on, M1 and M2 are turned on at the same time, and then M2 is turned off after a delay. At this time, M1 tube is turned on by Cgs bootstrap, and then M2 is turned on again after a delay, and finally M1 and M2 are turned off at the same time.

[0075] When the circuit is unloaded (the load is in an open circuit state) or lightly loaded (the load rate is generally below 30%-50%), the waveform is as follows: Figure 5 At this time, the circuit still uses bootstrap power supply, but due to the low frequency, the power generated by one bootstrap power supply cannot maintain the power consumed by the chip during the entire working cycle. After the chip works for multiple cycles, the Vcc capacitor will continue to discharge until the undervoltage protection. Therefore, when the circuit is unloaded or lightly loaded, the high-voltage power supply is turned on after a delay of a period of time after M1 and M2 are turned off to meet the power consumption requirements of the chip.

[0076] In another embodiment, the first switch tube M1 and the second switch tube M2 are voltage driven.

[0077] In this embodiment, the first switch tube M1 and the second switch tube M2 may be at least one of MOS, MESFET, JFET and the like, preferably NMOS.

[0078] In another embodiment, the source of the second switch tube is connected to a sampling resistor R2, and the input end of the sampling resistor R2 is connected to a control unit for monitoring the ILp current when the primary side is turned on. The control unit obtains and controls the current peak value of ILp in the primary circuit to achieve cycle-by-cycle overcurrent protection.

[0079] In another embodiment, the switching power supply circuit further includes a Brown out unit, the input end of the Brown out unit is connected to the common end of resistors R8 and R9, and the output end is connected to the PWM module, and is used to generate an undervoltage signal and output it to the PWM module to put the power supply into an undervoltage protection state when it is detected that the power supply Vin is lower than a preset threshold.

[0080] In this embodiment, when the primary side is turned on, the Brown out unit 3 generates a current to make the voltage at the common end of R8 and R9 equal to the voltage at the input end of the primary inductor Lp. Since the resistance of the current sampling R2 is very small, the power supply Vin is approximately equal to the voltage at the input end of the primary inductor Lp when the primary side is turned on. The voltage applied to both ends of R8 is approximately equal to the power supply Vin, so the output current I of the chip is prt = Vin / R8, by setting I prt With the reference current I bias Compare, when I prt <I bias After a period of time, the Brown out protection is triggered and a Brown out signal is generated, which is the input undervoltage protection.

[0081] In another embodiment, the switching power supply circuit further includes an absorption unit 6, which is used to prevent the occurrence of excessively high peak pulses at the moment of the switch tube being turned off from damaging the switch tube. The absorption unit includes a resistor R1, a capacitor C4 and a diode D1; wherein, after the resistor R1 and the capacitor C4 are connected in parallel, one end is connected to the positive electrode of the primary inductor Lp through the diode D1, and the other end is connected to the negative electrode of the primary inductor Lp.

[0082] In another embodiment, the switching power supply circuit further includes an output rectifying and filtering unit 7, which is used to convert AC power into half-wave DC power and further filter out the AC component to reduce ripple before output; the rectifying and filtering unit 7 includes a diode D2 and a capacitor C5.

[0083] In this embodiment, when the primary side of the transformer is cut off, the mutual inductance electromotive force of the secondary side causes the rectifier diode D2 to be turned on. On the one hand, the current flows into the load, and on the other hand, the capacitor C5 is charged and stored to release energy to the load when the primary side is turned on again.

[0084] It should be noted that the present disclosure innovatively proposes a design concept of integrating the rest of the switching power supply circuit except the Vcc charging capacitor inside the chip. Among them, one end of the overvoltage protection unit (OVP) 8 and the undervoltage protection unit (Brownout) 3 are respectively connected to the input end of the PWM module, and the other end is connected to the voltage signal acquisition unit through the prt pin for voltage signal acquisition in the control chip, and the gnd pin of the control chip is connected to the input end of the primary inductance Lp of the transformer, forming a floating ground structure design. The PWM module receives the current value of the main circuit when the primary side is turned on through the cs pin for current signal acquisition in the control chip, so as to start the overcurrent protection according to the monitoring result of the current peak. The PWM module receives the feedback of the output voltage through the FB pin for receiving the output voltage feedback information, so as to adjust the constant voltage output.

[0085] The above are only some embodiments of the present disclosure and are not intended to limit the inventive concept of the present disclosure. Those skilled in the art may make certain substitutions and modifications without departing from the principles of the inventive concept of the present disclosure, but all should fall within the protection scope of the present disclosure.

Claims

1. A dual-winding secondary-side feedback switching power supply, comprising: Primary side rectification and filtering unit, control unit, self-power supply unit, secondary side feedback unit, OVP unit, dual-winding transformer and voltage signal acquisition unit; among them, The primary side rectifying and filtering unit includes a rectifying bridge and a C1 capacitor, which is used to convert alternating current into direct current for input; The control unit includes a PWM module and a driving module, which are used to control the charging and discharging process of the self-powered unit and make corresponding adjustments to the circuit based on the received feedback information; The self-power supply unit is connected to the power supply Vin and the control unit respectively, and is used for storing energy and supplying power to the control unit; The self-powered unit includes a starting resistor, a first switch tube, a second switch tube, a Vcc charging capacitor management module and a Vcc charging capacitor; wherein, The Vcc charging capacitor is an energy storage capacitor of the self-powered unit; The drain of the first switch tube is connected to the power supply V in The source electrode is connected to the drain electrode of the second switch tube; and, The common end of the first switch tube and the second switch tube is connected through V cc Charging capacitor management module and V cc The charging capacitor is connected; The gates of the first switch tube and the second switch tube are connected to the driving module of the control unit; When the circuit is working normally, the first switch is turned on and the second switch is turned off, forming a power supply V in , a charging path from the first switch tube to the Vcc charging capacitor to achieve bootstrap power supply; When the first and second switch tubes are turned off at the same time, resulting in insufficient power supply to the circuit, the first switch tube is turned on to realize high voltage power supply; When the switching power supply is started, the power supply charges the gate-source parasitic capacitance Cgs of M1 through the starting resistor R1, raising the gate-source voltage Vgs of M1 to its threshold voltage Vth to turn on M1, forming a charging path from the power supply, M1 to the Vcc charging capacitor C2, charging Vcc to a preset value, and starting the control circuit; the Vcc charging capacitor management module is used to ensure the unidirectional conduction of the charging circuit, and to protect the switch tube M1 by limiting the current of the charging circuit. In addition, the Vcc charging capacitor management module may also be provided with a Vcc voltage detection module, and the detected Vcc voltage is fed back to the control circuit; When the switch power supply control circuit works normally, the control circuit first drives M1 and M2 in the switch circuit to turn on at the same time, and turns off M2 after a delay. At this time, the gate-source parasitic capacitance Cgs of M1 generates bootstrapping, and M1 maintains the on state, forming a charging path from the power supply, M1 to the charging capacitor C2, charging Vcc, and realizing bootstrap power supply; because M1 is in the bootstrap state at this time, the gate voltage is relatively large, M1 is in a saturated on state, and the voltage drop is extremely small; After Vcc is charged, M2 is turned on again under the control circuit, and the current flows from the input power supply through M1, M2, and the transformer primary inductance Lp to the ground, that is, the primary side is in the on state, and the transformer stores energy in this process; then M1 and M2 are turned off, and the primary side is cut off. Since the magnetic flux cannot change suddenly, the transformer secondary side induces a positive voltage at the top and a negative voltage at the bottom, and the secondary side continues to flow to release energy; When M1 and M2 are in the off state for a long time, resulting in insufficient Vcc power supply, the control circuit raises the gate voltage of M1 to Vcc, and at the same time, the power supply charges the gate of M1 through the start-up resistor R1, turning on M1 and providing high-voltage power supply; The secondary side feedback unit is provided with a feedback output terminal, one end of which is connected to the positive plate or negative plate of the energy storage capacitor of the self-powered unit, and the other end is connected to the PWM module, for detecting the change of the secondary side output signal and feeding back to the control unit; One end of the OVP unit is connected to the voltage signal acquisition unit, and the other end is connected to the PWM module to detect the output voltage V out When the preset threshold is exceeded, an OVP signal is generated and output to the PWM module to put the power supply into overvoltage protection state; The dual-winding transformer includes a primary inductor Lp and a secondary inductor Ls, wherein the positive electrode of Lp is connected to the switch tube of the self-power supply unit, and the negative electrode is grounded; One end of the voltage signal acquisition unit is grounded, and the other end is connected to the positive electrode of the primary inductor Lp.

2. The switching power supply according to claim 1, characterized in that: The voltage signal acquisition unit includes resistors R8 and R9, and a common end of the resistors R8 and R9 is connected to the OVP unit.

3. The switching power supply according to claim 1, characterized in that: The secondary side feedback unit includes a voltage stabilizing device, an optocoupler and a feedback auxiliary device; The optical coupler includes a light emitting diode and a phototransistor, and the collector and emitter of the phototransistor are feedback output ends; wherein, The collector and emitter of the phototransistor are feedback output terminals; The feedback auxiliary device includes a voltage dividing resistor.

4. The switching power supply according to claim 1, characterized in that: The bootstrap power supply is suitable for any of the following load circuits: no-load, light-load and heavy-load.

5. The switching power supply according to claim 1, characterized in that: The first switch tube and the second switch tube are voltage driven.

6. The switching power supply according to claim 1, characterized in that: The source of the second switch tube is connected to a sampling resistor, and the input end of the sampling resistor is connected to the control unit for monitoring the ILp current when the primary side is turned on. The control unit obtains and controls the current peak value of ILp in the primary circuit.

7. The switching power supply according to any one of claims 1 to 6, characterized in that: The switching power supply also includes an undervoltage protection unit, the input end of which is connected to the common end of resistors R8 and R9, and the output end is connected to the PWM module. When it is detected that the power supply Vin is lower than a preset threshold, an undervoltage signal is generated and output to the PWM module to put the power supply into an undervoltage protection state.

8. The switching power supply according to any one of claims 1 to 6, characterized in that: The switching power supply also includes an absorption unit, which includes a resistor R1, a capacitor C4 and a diode D1; wherein, after the resistor R1 and the capacitor C4 are connected in parallel, one end is connected to the positive electrode of the primary inductor Lp through the diode D1, and the other end is connected to the negative electrode of the primary inductor Lp.

9. The switching power supply according to any one of claims 1 to 6, characterized in that: The switching power supply also includes an output rectification and filtering unit, which is used to convert AC power into half-wave DC power and further filter out the AC component to reduce ripple before output; the rectification and filtering unit includes a diode and a capacitor.

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