A DC power supply output anti-backflow circuit and control method

Abstract

The present invention discloses a DC power supply output backflow prevention circuit, which includes: a first switch circuit, a second switch circuit, a third switch circuit, an auxiliary power supply circuit and a control unit, wherein the first switch circuit is connected between the output end of the DC power supply output circuit and the input end of the load, the second switch circuit is connected between the output end of the auxiliary power supply circuit and the input end of the load, the third switch circuit is connected between the control end of the first switch circuit and the output end of the auxiliary power supply circuit, the input end of the auxiliary power supply circuit is connected to the output end of the DC power supply output circuit, the control unit is connected to the control end of the auxiliary power supply circuit through a first isolation circuit, and the control unit is connected to the control end of the first switch circuit through a second isolation circuit. The backflow prevention circuit designed by the present invention can not only solve the problem of slow backflow of small currents, but also realize the fault isolation function, thereby improving the reliability of the DC power supply output circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic circuits, and more specifically, to a direct current power supply output backflow prevention circuit and a control method. Background Art

[0002] The function of the anti-backflow circuit of the commonly used AC / DC or DC / DC power supply is to ensure that the power supply monomers work independently of each other, and to prevent backflow and isolate output faults. The anti-backflow current can use a simple diode circuit or a slightly more complex MOSFET circuit. The former is simple and reliable, but it is only suitable for high-voltage and low-current working conditions. Under low-voltage and high-current conditions, due to the existence of the diode conduction voltage drop, it will significantly affect the power supply efficiency and bring many technical problems such as device heat dissipation. The solution using the MOSFET circuit can significantly improve the efficiency due to the low on-resistance, but the circuit is more complicated and puts forward higher requirements on the control method. The control of the anti-backflow circuit can be realized by using a dedicated chip, or it can be realized by forming a functional circuit with discrete devices.

[0003] For example, in the case of a MOSFET circuit, under certain working conditions, the slow backflow current is very small and will not trigger the anti-backflow circuit, causing the voltage inside and outside the circuit to rise synchronously, which may eventually damage the DC power supply output circuit components. Secondly, there is a contradiction between the sensitivity of the anti-backflow and the power efficiency. The sensitivity of the anti-backflow circuit depends on the on-resistance of the MOSFET. The higher the on-resistance, the more sensitive the anti-backflow circuit is, but it will reduce the power efficiency. In addition, under the condition of output overvoltage, the traditional anti-backflow circuit lacks the function of self-safety isolation, which causes damage to the anti-backflow circuit.

[0004] Therefore, how to solve the problem of slow backflow of small current, realize the fault isolation function, and improve the reliability of the DC power supply output circuit has become a technical problem to be solved urgently and a research focus for technical personnel in this field. Summary of the invention

[0005] In order to solve the technical problem of the slow backflow of small current in the existing anti-backflow circuit, the present invention innovatively provides a DC power supply output anti-backflow circuit, which can not only solve the problem of slow backflow of small current, but also realize the fault isolation function, thereby improving the reliability of the DC power supply output circuit.

[0006] To achieve the above technical objectives, an embodiment of the present invention discloses a DC power supply output backflow prevention circuit, including a DC power supply output circuit and a load, wherein the output end of the DC power supply output circuit is connected to the input end of the load, and the backflow prevention circuit includes: a first switch circuit, a second switch circuit, a third switch circuit, an auxiliary power supply circuit and a control unit, wherein the first switch circuit is connected between the output end of the DC power supply output circuit and the input end of the load, the second switch circuit is connected between the output end of the auxiliary power supply circuit and the input end of the load, the third switch circuit is connected between the control end of the first switch circuit and the output end of the auxiliary power supply circuit, the input end of the auxiliary power supply circuit is connected to the output end of the DC power supply output circuit, the control unit is connected to the control end of the auxiliary power supply circuit through a first isolation circuit, and the control unit is connected to the control end of the first switch circuit through a second isolation circuit.

[0007] Furthermore, the present invention provides a DC power supply output backflow prevention circuit, wherein the first isolation circuit includes a first photocoupler, the two ends of the diode in the first photocoupler are connected to the control unit, and the collector and emitter of the transistor in the first photocoupler are connected to the enable end of the auxiliary power supply circuit.

[0008] Furthermore, the present invention provides a DC power supply output backflow prevention circuit, wherein the first switching circuit includes a MOS switch tube, the gate of the MOS switch tube is connected to the output end of the auxiliary power supply circuit through a first current limiting element, the source of the MOS switch tube is connected to the positive electrode of the DC power supply output circuit, and the drain of the MOS switch tube is connected to the positive electrode of the load.

[0009] Furthermore, the present invention provides a DC power supply output backflow prevention circuit, wherein the second switching circuit includes a first transistor, the collector of the first transistor is connected between the drain of the MOS switch tube and the positive electrode of the load, and the base and emitter of the first transistor are connected to the output end of the auxiliary power supply circuit through a second current limiting element.

[0010] Furthermore, the present invention provides a DC power supply output backflow prevention circuit, wherein the third switching circuit includes a second triode, the base set of the second triode is connected to the second current limiting element through a third current limiting element, the emitter of the second triode is connected to the source of the MOS switch tube, and the collector of the second triode is connected between the gate of the MOS switch tube and the first current limiting element.

[0011] Furthermore, the present invention provides a DC power supply output backflow prevention circuit, wherein the second isolation circuit includes a second photocoupler, both ends of the diode in the second photocoupler are connected to the control unit, the collector of the transistor in the second photocoupler is connected to the gate of the MOS switch tube, and the emitter of the transistor in the second photocoupler is connected to the source of the MOS switch tube.

[0012] Furthermore, the present invention provides a DC power supply output backflow prevention circuit, which also includes a voltage regulator diode, the positive electrode of the voltage regulator diode is connected between the source of the MOS switch tube and the emitter of the second transistor, and the negative electrode of the voltage regulator diode is connected between the gate of the MOS switch tube and the collector of the second transistor.

[0013] Furthermore, the present invention provides a DC power supply output backflow prevention circuit, which includes a polarized capacitor, wherein the positive electrode of the polarized capacitor is connected between the DC power supply output circuit and the source of the MOS switch tube, and the negative electrode of the polarized capacitor is connected between the DC power supply output circuit and the negative electrode of the load.

[0014] The present invention also provides a control method for a DC power supply output backflow prevention circuit, using the above-mentioned DC power supply output circuit to output the backflow prevention circuit, the method comprising:

[0015] The control unit detects the output voltage of the DC power supply output circuit in real time according to a fixed frequency;

[0016] When the output voltage of the DC power supply output circuit is higher than a set voltage threshold, the control unit controls the second isolation circuit to disconnect the first switch circuit;

[0017] When the output voltage of the DC power supply output circuit is within the set voltage threshold range and the DC power supply output circuit enters the intermittent output mode, the time length for which the DC power supply output circuit enters the intermittent output mode is accumulated. When the accumulated time length for which the DC power supply output circuit enters the intermittent output mode exceeds the set time threshold, the control unit controls the second isolation circuit to disconnect the first switch circuit.

[0018] Furthermore, the present invention provides a DC power supply output anti-backflow circuit method, which also includes:

[0019] When the anti-backflow circuit fails, the control unit controls the second isolation circuit to disconnect the first switch circuit;

[0020] The control unit determines the fault type of the DC power supply output circuit, wherein the fault type includes output overvoltage fault, input overvoltage fault and overheating fault;

[0021] When the fault type is an output overvoltage fault, the control power supply controls the first isolation circuit to disconnect the auxiliary power supply circuit.

[0022] The beneficial effects of the present invention are as follows: the present invention is provided with a first switch circuit, a second switch circuit, a third switch circuit, an auxiliary power supply circuit and a control unit, wherein the first switch circuit is connected between the output end of the DC power supply output circuit and the input end of the load, the second switch circuit is connected between the output end of the auxiliary power supply circuit and the input end of the load, the third switch circuit is connected between the control end of the first switch circuit and the output end of the auxiliary power supply circuit, the input end of the auxiliary power supply circuit is connected to the output end of the DC power supply output circuit, the control unit is connected to the control end of the auxiliary power supply circuit through the first isolation circuit, and the control unit is connected to the control end of the first switch circuit through the second isolation circuit, thereby forming a DC power supply output anti-backflow circuit that can not only solve the problem of slow backflow of small currents, but also realize the fault isolation function, thereby improving the reliability of the DC power supply output circuit. In practical application, as long as the current backflow phenomenon occurs in the circuit, even if the small current slow backflow control unit will disconnect the first switch circuit through the second isolation circuit, so that a circuit is formed between the DC power supply output circuit and the load. Therefore, the current of the load cannot pass through the first switch circuit, that is, the current output by the load cannot flow back into the DC power supply output circuit; when the anti-backflow circuit fails, the control unit will control the auxiliary power supply circuit to cut off power through the first isolation circuit, so that the first switch circuit, the second switch circuit and the third switch circuit are in a power-off state, which plays an isolation role and protects the anti-backflow circuit; thereby improving the reliability of the operation of the DC power supply output circuit from the above two aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of a DC power supply output backflow prevention circuit of the present invention;

[0024] Figure 2 The present invention is a flowchart of an embodiment of a method for controlling a DC power supply output backflow prevention circuit. DETAILED DESCRIPTION

[0025] A DC power supply output backflow prevention circuit of the present invention is explained and illustrated in detail below in conjunction with the accompanying drawings of the specification.

[0026] like Figure 1As shown, the embodiment of the present invention discloses a DC power supply output backflow prevention circuit, which specifically includes a DC power supply output circuit 1 and a load 2. The DC power supply output circuit 1 can use a rectifier bridge composed of four silicon rectifiers to realize the output of DC power. The output end of the DC power supply output circuit 1 is connected to the input end of the load 2 to provide DC power to the load 2. The backflow prevention circuit specifically includes: a first switch circuit 3, a second switch circuit 4, a third switch circuit 5, an auxiliary power supply circuit 6 and a control unit 7. Among them, the first switch circuit 3 is connected between the output end of the DC power supply output circuit 1 and the input end of the load 2, and the first switch circuit 3 is used to control the on-off between the DC power supply output circuit 1 and the load 2; the second switch circuit 4 is connected between the output end of the auxiliary power supply circuit 6 and the input end of the load 2, and the second switch circuit 4 is used to provide a higher reverse breakdown voltage to protect the normal operation of the auxiliary power supply circuit 6; the third switch circuit 5 is connected between the control end of the first switch circuit 3 and the output end of the auxiliary power supply circuit 6, and the third switch circuit 5 is used to control the on-off of the first switch circuit 3; the input end of the auxiliary power supply circuit 6 and the output end of the DC power supply output circuit 1 The auxiliary power supply circuit 6 is used to provide working voltage for the first switch circuit 3, the second switch circuit 4 and the third switch circuit 5. The auxiliary power supply circuit 6 can preferably use a flyback switch power supply circuit; the control unit 7 is connected to the control end of the auxiliary power supply circuit 6 through the first isolation circuit 8, and the control unit 7 is connected to the control end of the first switch circuit 3 through the second isolation circuit 9. The control unit 7 is used to control the on-off of the auxiliary power supply circuit 6 by controlling the first isolation circuit 8, disconnect the auxiliary power supply circuit 6 when a fault occurs in the anti-backflow circuit, and control the on-off of the first switch circuit 3 by controlling the second isolation circuit 9, and disconnect the first switch circuit 3 when current backflow occurs.

[0027] Of course, those skilled in the art can understand that the control unit 7 can adopt a DSP (Digital Signal Processing) digital signal processor, an FPGA (Field-Programmable Gate Array) field programmable gate array, an MCU (Microcontroller Unit) system board, a SoC (system on a chip) system board or a PLC (Programmable Logic Control) minimum system including I / O, and realize the above functions of the control unit 7 through built-in logic and threshold setting.

[0028] In actual application, under normal circumstances, the first switch circuit 3 is turned on, and the DC power output circuit 1 normally provides power to the load 2; as long as the current backflow phenomenon occurs in the circuit, even if it is a small current that flows back slowly, the control unit 7 will disconnect the first switch circuit 3 through the second isolation circuit 9, so that a circuit is formed between the DC power output circuit 1 and the load 2. Therefore, the current of the load 2 cannot pass through the first switch circuit 3, that is, the current output by the load 2 cannot flow back to the DC power output circuit 1; when the anti-backflow circuit fails, the control unit 7 will control the auxiliary power supply circuit 6 to cut off the power through the first isolation circuit 8, so that the first switch circuit 3, the second switch circuit 4 and the third switch circuit 5 are in a power-off state, which plays an isolation role and protects the first switch circuit 3, the second switch circuit 4 and the third switch circuit 5 from being damaged; thereby improving the reliability of the operation of the DC power output circuit 1 from the above two aspects.

[0029] In one embodiment of the present invention, the first isolation circuit 8 includes a first photocoupler O1, the two ends of the diode in the first photocoupler O1 are connected to the control unit 7, and the collector and emitter of the transistor in the first photocoupler O1 are connected to the enable end of the auxiliary power supply circuit 6. The enable end of the auxiliary power supply circuit 6 is a control end that controls whether the auxiliary power supply circuit 6 works. More specifically, under normal circumstances, the control unit 7 outputs a low level, the diode in the first photocoupler O1 is turned off, the transistor in the first photocoupler O1 is not turned on, the enable end of the auxiliary power supply circuit 6 is enabled, and the auxiliary power supply circuit 6 works normally; when the control unit 7 detects that the anti-backflow circuit has a fault, the control unit 7 outputs a high level, the diode in the first photocoupler O1 lights up, the transistor in the first photocoupler O1 is turned on to pull down the enable end voltage of the auxiliary power supply circuit 6, the auxiliary power supply circuit 6 is disconnected and does not work, and the anti-backflow circuit cannot work when the power is off.

[0030] In one embodiment of the present invention, the first switch circuit 3 includes a MOS switch tube M1, the gate of the MOS switch tube M1 is connected to the output end of the auxiliary power supply circuit 6 through the first current limiting element R1, the source of the MOS switch tube M1 is connected to the positive electrode of the DC power output circuit 1, and the drain of the MOS switch tube M1 is connected to the positive electrode of the load 2. The switching between the DC power output circuit 1 and the load 2 is realized by controlling the switching of the source and drain of the MOS switch tube M1 through the gate of the MOS switch tube M1. The first current limiting element R1 can prevent the MOS switch tube M1 from generating an oscillating waveform during the switching process, increase the switching loss of the MOS switch tube M1, and prevent the MOS switch tube M1 from being broken down. Generally, a parasitic diode is connected in series between the source and drain of the MOS switch tube M1. When a large instantaneous reverse current is generated in the circuit, it can be led out through the parasitic diode, protecting the source and drain of the MOS switch tube M1, and preventing the MOS switch tube M1 from being broken down, so as to further improve the reliability of the operation of the DC power output circuit 1.

[0031] In one embodiment of the present invention, the second switch circuit 4 includes a first transistor Q1, the collector of the first transistor Q1 is connected between the drain of the MOS switch tube M1 and the positive electrode of the load 2, and the base set and emitter of the first transistor Q1 are connected to the output end of the auxiliary power supply circuit 6 through the second current limiting element R2. The second current limiting element R2 plays a role in hindering and reducing the base current, so that the base current of the first transistor Q1 works within the allowable range, so as to ensure the reliable stability of the operation of the first transistor Q1 and prevent the first transistor Q1 from accidentally turning on. The base set and collector of the first transistor Q1 are short-circuited to form a diode structure, and its reverse breakdown voltage is at least 40V, which provides reverse breakdown protection for the auxiliary power supply circuit 6, so as to further improve the reliability of the operation of the DC power output circuit 1.

[0032] In one embodiment of the present invention, the third switch circuit 5 includes a second triode Q2, the base set of the second triode Q2 is connected to the second current limiting element R2 through the third current limiting element R3, the emitter of the second triode Q2 is connected to the source of the MOS switch tube M1, and the collector of the second triode Q2 is connected between the gate of the MOS switch tube M1 and the first current limiting element R1. The third current limiting element R3 plays a role in hindering and reducing the base current, so that the base current of the second triode Q2 works within the allowable range, so as to ensure the reliable stability of the second triode Q2 and prevent the second triode Q2 from accidentally turning on. The voltage drop between the collector and the emitter of the second transistor Q2 is the voltage VGS between the gate and the source of the MOS switch tube M1. When there is output backflow, due to the on-resistance on the MOS switch tube M1, there will be a reverse voltage drop on the on-resistance. When the reverse voltage drop acts on the third current limiting element R3, the second transistor Q2 can operate in the linear region. After the gate voltage VGS of the MOS switch tube M1 is lowered, the MOS switch tube M1 is turned off, thereby playing a blocking role.

[0033] In one embodiment of the present invention, the reverse voltage drop is not enough to enable the second transistor Q2 to work in the linear region under low current conditions and thus cannot play a blocking role. In order to improve the sensitivity of the MOS switch tube M1, it is necessary to adjust the resistance values ​​of the first current limiting element R1, the second current limiting element R2 and the third current limiting element R3, so that the gate voltage VGS of the MOS switch tube M1 will be reduced, thereby increasing the loss. In order to compensate for this defect, the second isolation circuit 9 includes a second photocoupler O2, the two ends of the diode in the second photocoupler are connected to the control unit 7, the collector of the transistor in the second photocoupler O2 is connected to the gate of the MOS switch tube M1, and the emitter of the transistor in the second photocoupler O2 is connected to the source of the MOS switch tube M1. Under normal circumstances, the control unit 7 outputs a low level, the diode in the second optical coupler is turned off, the transistor in the second photocoupler O2 is not turned on, and the MOS switch tube M1 works normally; when the control unit 7 detects that a small current is slowly flowing back, the control unit 7 outputs a high level, the diode in the second optical coupler lights up, the transistor in the second photocoupler O2 is turned on, and the transistor in the second photocoupler O2 pulls down the voltage VGS between the gate and the drain of the MOS switch tube M1, turning off the MOS switch tube M1, so as to prevent the small current from slowly flowing back. There is no need to adjust the resistance of the first current limiting element R1, the second current limiting element R2, and the third current limiting element R3, thereby avoiding power loss, solving the contradiction between the sensitivity of the anti-backflow circuit and the power efficiency, and further improving the reliability of the operation of the DC power supply output circuit 1.

[0034] In one embodiment of the present invention, a voltage stabilizing diode is further included, wherein the positive electrode of the voltage stabilizing diode is connected between the source of the MOS switch tube M1 and the emitter of the second triode Q2, and the negative electrode of the voltage stabilizing diode VZ1 is connected between the gate of the MOS switch tube M1 and the collector of the second triode Q2. The voltage stabilizing diode can absorb the instantaneous high voltage generated on the MOS switch tube M1 and the second triode Q2, thereby preventing the MOS switch tube M1 and the second triode Q2 from being broken down by the instantaneous high voltage, and further improving the reliability of the operation of the DC power supply output circuit 1.

[0035] In one embodiment of the present invention, a polarized capacitor C is included, the positive electrode of the polarized capacitor C is connected between the DC power output circuit 1 and the source of the MOS switch tube M1, and the negative electrode of the polarized capacitor C is connected between the DC power output circuit 1 and the negative electrode of the load 2. The polarized capacitor C can compensate for the reactive power of the load 2, increase the power factor, improve the voltage quality output by the DC power output circuit 1 and reduce circuit loss, and adjust the output voltage waveform so that the output voltage is stabilized at a smooth average value, further improving the reliability of the operation of the DC power output circuit 1.

[0036] like Figure 2As shown, an embodiment of the present invention further provides a control method for a DC power supply output anti-backflow circuit, using the above-mentioned DC power supply output circuit 1 to output an anti-backflow circuit, the method comprising:

[0037] The control unit 7 detects the output voltage of the DC power supply output circuit 1 in real time according to a fixed frequency;

[0038] When the output voltage of the DC power supply output circuit 1 is higher than the set voltage threshold, the control unit 7 controls the second isolation circuit 9 to disconnect the first switch circuit 3; for example, the voltage threshold is set to a set voltage value or 15% higher than the set voltage value.

[0039] When the output voltage of the DC power supply output circuit 1 is within the set voltage threshold range and the DC power supply output circuit 1 enters the intermittent output mode, the duration of the DC power supply output circuit 1 entering the intermittent output mode is accumulated. When the accumulated duration of the DC power supply output circuit 1 entering the intermittent output mode exceeds the set time threshold, the control unit 7 controls the second isolation circuit 9 to disconnect the first switch circuit 3.

[0040] In another embodiment of the present invention, when the anti-backflow circuit fails, the control unit 7 controls the second isolation circuit 9 to disconnect the first switch circuit 3;

[0041] The control unit 7 determines the fault type of the DC power supply output circuit 1, and the fault type includes output overvoltage fault, input overvoltage fault and overheating fault;

[0042] When the fault type is an output overvoltage fault, the control power supply controls the first isolation circuit 8 to disconnect the auxiliary power supply circuit 6 .

[0043] This method embodiment provides an anti-backflow circuit action mechanism and formulates a unified action threshold, which solves the problem of different anti-backflow circuit action thresholds caused by different load devices, and is conducive to the consistent control of different load devices. Through the above control strategy, it is possible to achieve complete control of the anti-backflow circuit. No matter what kind of external output fault or backflow phenomenon occurs, the anti-backflow circuit can work normally and play a role of blocking and isolation.

[0044] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0045] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and simple improvements made to the essential contents of the present invention should be included in the protection scope of the present invention.

Claims

1. A DC power supply output backflow prevention circuit, comprising a DC power supply output circuit and a load, wherein the output end of the DC power supply output circuit is connected to the input end of the load, and characterized in that: The anti-backflow circuit includes: a first switch circuit, a second switch circuit, a third switch circuit, an auxiliary power supply circuit and a control unit, wherein the first switch circuit is connected between the output end of the DC power supply output circuit and the input end of the load, the second switch circuit is connected between the output end of the auxiliary power supply circuit and the input end of the load, the third switch circuit is connected between the control end of the first switch circuit and the output end of the auxiliary power supply circuit, the input end of the auxiliary power supply circuit is connected to the output end of the DC power supply output circuit, the control unit is connected to the control end of the auxiliary power supply circuit through a first isolation circuit, the control unit is connected to the control end of the first switch circuit through a second isolation circuit, the first switch circuit includes a MOS switch tube, and the gate of the MOS switch tube The first current limiting element is connected to the output end of the auxiliary power supply circuit, the source of the MOS switch tube is connected to the positive electrode of the DC power supply output circuit, the drain of the MOS switch tube is connected to the positive electrode of the load, the second switch circuit includes a first triode, the collector of the first triode is connected between the drain of the MOS switch tube and the positive electrode of the load, the base and emitter of the first triode are connected to the output end of the auxiliary power supply circuit through the second current limiting element, the third switch circuit includes a second triode, the base of the second triode is connected to the second current limiting element through the third current limiting element, the emitter of the second triode is connected to the source of the MOS switch tube, and the collector of the second triode is connected between the gate of the MOS switch tube and the first current limiting element.

2. A DC power supply output backflow prevention circuit according to claim 1, characterized in that: The first isolation circuit includes a first photoelectric coupler, wherein two ends of a diode in the first photoelectric coupler are connected to a control unit, and a collector and an emitter of a transistor in the first photoelectric coupler are connected to an enable end of an auxiliary power supply circuit.

3. The DC power supply output backflow prevention circuit according to claim 1, characterized in that: The second isolation circuit includes a second photocoupler, wherein both ends of a diode in the second photocoupler are connected to a control unit, a collector of a transistor in the second photocoupler is connected to a gate of a MOS switch tube, and an emitter of the transistor in the second photocoupler is connected to a source of the MOS switch tube.

4. The DC power supply output backflow prevention circuit according to claim 1, characterized in that: It also includes a voltage stabilizing diode, the anode of which is connected between the source of the MOS switch tube and the emitter of the second transistor, and the cathode of which is connected between the gate of the MOS switch tube and the collector of the second transistor.

5. The DC power supply output backflow prevention circuit according to claim 1, characterized in that: It comprises a polar capacitor, wherein the positive electrode of the polar capacitor is connected between the DC power supply output circuit and the source of the MOS switch tube, and the negative electrode of the polar capacitor is connected between the DC power supply output circuit and the negative electrode of the load.

6. A control method for a DC power supply output anti-backflow circuit, characterized in that: Using a DC power supply output circuit output anti-backflow circuit as claimed in claim 1, the method comprises: The control unit detects the output voltage of the DC power supply output circuit in real time according to a fixed frequency; When the output voltage of the DC power supply output circuit is higher than a set voltage threshold, the control unit controls the second isolation circuit to disconnect the first switch circuit; When the output voltage of the DC power supply output circuit is within the set voltage threshold range and the DC power supply output circuit enters the intermittent output mode, the time length for which the DC power supply output circuit enters the intermittent output mode is accumulated. When the accumulated time length for which the DC power supply output circuit enters the intermittent output mode exceeds the set time threshold, the control unit controls the second isolation circuit to disconnect the first switch circuit.

7. A control method for a DC power supply output backflow prevention circuit according to claim 6, characterized in that: Also includes: When the anti-backflow circuit fails, the control unit controls the second isolation circuit to disconnect the first switch circuit; The control unit determines the fault type of the DC power supply output circuit, wherein the fault type includes output overvoltage fault, input overvoltage fault and overheating fault; When the fault type is an output overvoltage fault, the control power supply controls the first isolation circuit to disconnect the auxiliary power supply circuit.

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