Anti-backflow high-voltage starting circuit

Abstract

The invention discloses an anti-backflow high-voltage starting circuit, which comprises a first voltage division circuit, a starting current generation circuit, an anti-backflow circuit, a second voltage division circuit and a threshold comparison circuit, the first voltage division circuit is used for detecting an input voltage of a VIN end and dividing the input voltage to generate a negative input voltage AVIN; the starting current generating circuit is used for generating starting current; the anti-backflow circuit is used for generating a mirror current and blocking a backflow current flowing from a VDD end to a VIN end; the second voltage division circuit is used for detecting the output voltage of the VDD end and dividing the output voltage to generate a first forward input voltage AVDD1 and a second forward input voltage AVDD2; the threshold value comparison circuit comprises a comparator COMP1 and a comparator COMP2; the voltage of the VIN end and the voltage of the VDD end are detected through the first voltage division circuit and the second voltage division circuit in a voltage division mode respectively, the voltage of the VIN end and the voltage of the VDD are monitored in real time, and the problem that when VIN is smaller than VDD and VDD does not exceed a voltage threshold value, current flows backwards can be effectively solved.

Description

Technical Field

[0001] The invention belongs to the field of integrated circuits, and in particular relates to a backflow prevention high-voltage starting circuit. Background Art

[0002] As an efficient power supply technology, switching power supply is widely used in various electronic products and equipment with its excellent energy-saving and power-saving characteristics. The switching power converter consists of two parts, namely the control module and the power module. The control module of the switching power converter adjusts the power module in time according to the changes in input conditions (voltage or current) and output conditions (voltage or current), and converts one form of power into another form of power. Generally, the switching power converter requires a startup circuit to stabilize the control module when the switching power converter is just powered on. After the control module works normally, the switching power converter officially starts working. In related technologies, a resistor is usually used to charge the capacitor. When the voltage of the capacitor reaches the startup voltage, the control module is powered. The power consumption of the startup circuit depends on the resistance value of the resistor. The larger the resistance, the smaller the power consumption of the startup circuit, but the longer the startup time; the smaller the resistance, the shorter the startup time, but the greater the power consumption of the startup circuit. Therefore, this charging method must compromise between startup time and power consumption.

[0003] In the prior art, the startup of the switching power supply control chip is achieved through a startup resistor or a high-voltage startup circuit. However, to achieve high efficiency and energy saving, the energy consumption caused by the startup resistor method cannot be ignored. In theory, the energy consumption can be reduced by increasing the startup resistor, but it will lead to a significant increase in the startup time. The design idea of ​​the high-voltage startup circuit is that during the system startup phase, the high-voltage input terminal provides a startup current to the bypass capacitor C of the VDD pin. VDD When VDD is higher than the threshold voltage of the overvoltage protection module, the startup current is turned off and the VDD pin is powered by the auxiliary winding of the peripheral transformer.

[0004] Traditional high voltage starting circuit such as Figure 1 As shown in the figure, when VIN>VDD and VDD does not exceed the voltage threshold, the xEN signal is low, VDDOVP is high, and the VIN terminal provides a startup current to charge the VDD terminal; when VIN>VDD and VDD exceeds the voltage threshold, the xEN signal is high, VDDOVP is low, the startup circuit is turned off, and the peripheral winding supplies power to the VDD port. At this time, the anti-backflow tube PM3 is turned off, and there is no backflow current in the startup circuit even if VDD>VIN; however, when VIN<VDD and VDD does not exceed the voltage threshold, the anti-backflow tube PM3 is in the open state, and the parasitic diode does not work. At this time, a large backflow current will be generated from the VDD terminal to the VIN terminal, affecting the use of the system. Summary of the invention

[0005] The present invention aims to overcome at least one defect (shortcoming) in the above-mentioned prior art, and adopts a voltage-dividing resistor to respectively detect the voltage of the VIN terminal and the VDD terminal, and compares the two through a comparator COMP2, and monitors the voltage of VIN and VDD in real time. The output of the comparator COMP2 is synchronously used as an enable signal of the startup circuit. When VIN<VDD and VDD does not exceed the voltage threshold, the anti-backflow tube PM3 is turned off, and the parasitic diode is used to block the backflow current to solve the current backflow problem when VIN<VDD and VDD does not exceed the voltage threshold, and has no effect on the high-voltage startup function under the state of VIN>VDD.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] An embodiment of the present invention provides a high-voltage startup circuit for preventing backflow, and the high-voltage startup circuit for preventing backflow includes:

[0008] A first voltage-dividing circuit, a starting current generating circuit, a backflow prevention circuit, a second voltage-dividing circuit and a threshold comparison circuit;

[0009] The first voltage divider circuit is used to detect the input voltage at the VIN terminal and divide the voltage to generate a negative input voltage AVIN;

[0010] The starting current generating circuit is used to generate a starting current;

[0011] The anti-backflow circuit is used to generate a mirror current and block the backflow current flowing from the VDD terminal to the VIN terminal;

[0012] The second voltage divider circuit is used to detect the output voltage of the VDD terminal and divide the voltage to generate a first positive input voltage AVDD1 and a second positive input voltage AVDD2;

[0013] The threshold comparison circuit includes a comparator COMP1 and a comparator COMP2;

[0014] The comparator COMP1 is used to detect whether the first positive input voltage is greater than a reference voltage, and to control the shutdown of the anti-backflow circuit and the startup current generating circuit when it is confirmed that the first positive input voltage is greater than the reference voltage; the comparator COMP2 is used to compare the negative input voltage AVIN and the second positive input voltage AVDD2, and to control the shutdown of the anti-backflow circuit when it is confirmed that the second positive input voltage AVDD2 is greater than the negative input voltage AVIN.

[0015] Optionally, the first voltage divider circuit includes a resistor R1 and a resistor R2, the first end of the resistor R1 is connected to the VIN terminal, the second end of the resistor R1 is connected to the first end of the resistor R2, the second end of the resistor R2 is connected to the ground terminal, and the output point of the negative input voltage AVIN is the connection point between the resistor R1 and the resistor R2.

[0016] Optionally, the startup current generating circuit includes a resistor R3, a diode D1, a switch tube NM3, a switch tube NM1, a switch tube PM1 and a reference current source IREF; the gate of the switch tube NM3 is connected to an enable signal xEN to control the switching of the switch tube NM3;

[0017] When the enable signal xEN is at a high level, the switch tube NM3 is turned off, and the startup current generating circuit does not work;

[0018] When the enable signal xEN is at a low level, the switch tube NM3 is turned on, and the startup current generating circuit works.

[0019] Optionally, the anti-backflow circuit includes a diode D2, a switch tube PM2, a switch tube PM3, a resistor R4, a resistor R5 and a switch tube NM2; the gate of the switch tube NM2 is connected to an enable signal VDDOVP to control the switching of the switch tube NM2;

[0020] When the enable signal VDDOVP is at a high level, the switch tube NM2 is turned on, so that the switch tube PM3 is turned on, and the startup current flows from the VIN terminal to the VDD terminal;

[0021] When the enable signal VDDOVP is at a low level, the switch tube NM2 is turned off, so that the switch tube PM3 is turned off, thereby blocking the backflow current from the VDD terminal to the VIN terminal.

[0022] Optionally, the second voltage divider circuit includes resistor R6, resistor R7 and resistor R8, the first end of the resistor R6 is connected to the VDD terminal, the second end of the resistor R6 is connected to the ground terminal through the resistor R7 and the resistor R8 in sequence, the output point of the first positive input voltage is the connection point between the resistor R6 and the resistor R7, and the output point of the second positive input voltage is the connection point between the resistor R7 and the resistor R8.

[0023] Optionally, one end of the resistor R3 is electrically connected to the VIN terminal, the second end of the resistor R3 is respectively connected to the cathode of the diode D1, the drain of the switch tube NM3 and the gate of the switch tube NM1, the anode of the diode D1 is electrically connected to the source and GND terminal of the switch tube NM3, and the gate of the switch tube NM3 is connected to the enable signal xEN; the source of the switch tube PM1 is electrically connected to the VIN terminal, the gate and drain of the switch tube PM1 are both connected to the anti-backflow circuit, the source of the switch tube NM1 is electrically connected to one end of the reference current source IREF; the second end of the reference current source IREF is electrically connected to the GND terminal.

[0024] Optionally, the cathode of the diode D2 is electrically connected to the VIN terminal, and the anode of the diode D2 is connected to the gate of the switch tube PM2 and the starting current generating circuit; the source of the switch tube PM2 is electrically connected to the VIN terminal, the drain of the switch tube PM2 is electrically connected to the drain of the switch tube PM3, the gate of the switch tube PM3 is electrically connected to the first end of the resistor R4 and the first end of R5 respectively, the source of the switch tube PM3 is connected to the second end of the resistor R4 and the VDD terminal, the second end of the resistor R5 is electrically connected to the drain of the switch tube NM2, the gate of the switch tube NM2 is connected to the enable signal VDDOVP, and the source of the switch tube NM2 is electrically connected to the GND terminal.

[0025] Optionally, the threshold comparison circuit also includes an inverter INV1, an inverter INV2 and an AND gate AND, the non-inverting input terminal of the comparator COMP1 is connected to the first positive input voltage AVDD1, the inverting input terminal of the comparator COMP1 is connected to the reference voltage VREF, the output terminal of the comparator COMP1 is electrically connected to the input terminal of the inverter INV1; the output terminal of the inverter INV1 is electrically connected to the first terminal of the AND gate AND; the non-inverting input terminal of the comparator COMP2 is connected to the second positive input voltage AVDD2, the inverting input terminal of the comparator COMP2 is connected to the negative input voltage AVIN, the output terminal of the comparator COMP2 is electrically connected to the input terminal of the inverter INV2, the output terminal of the inverter INV2 is electrically connected to the second terminal of the AND gate AND, and the output terminal of the AND gate AND outputs an enable signal VDDOVP.

[0026] The beneficial effects of the present invention are:

[0027] The present invention detects the voltages of the VIN terminal and the VDD terminal respectively by means of voltage division through the first voltage division circuit and the second voltage division circuit, and compares the two through the comparator COMP2 in the threshold comparison circuit, monitors the voltages of VIN and VDD in real time, and the output of the comparator COMP2 is synchronously used as the enable signal of the startup circuit. When VIN<VDD and VDD does not exceed the voltage threshold, the anti-backflow switch PM3 is turned off, and the backflow current is blocked by the parasitic diode, which can effectively solve the current backflow problem when VIN<VDD and VDD does not exceed the voltage threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the schematic diagram of the traditional high voltage starting circuit;

[0029] Figure 2 is a circuit diagram of an embodiment of the present invention;

[0030] Figure 3 This is a simulation diagram of the reverse current from VDD to VIN in a traditional high-voltage startup circuit under the conditions of VIN = 9V, VDD = 9~25V;

[0031] Figure 4 This is a simulation diagram of the reverse current from VDD to VIN under the condition of VIN=9V, VDD=9-25V according to the embodiment of the present invention;

[0032] Figure 5 This is a simulation diagram of the startup current from VIN to VDD under the conditions of VIN=9-100V and VDD=8V according to an embodiment of the present invention;

[0033] Figure 6 This is a simulation diagram of the startup current from VIN to VDD under the conditions of VIN=9-100V and VDD=12V according to an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The present invention and its beneficial effects will be further described in detail below in conjunction with specific implementations and the accompanying drawings, but the specific implementations of the present invention are not limited thereto.

[0035] Figure 2 : is a circuit schematic diagram of an embodiment of the present invention, which provides an anti-backflow high-voltage startup circuit, which specifically includes a first voltage divider circuit 100, a startup current generating circuit 200, an anti-backflow circuit 300, a second voltage divider circuit 400 and a threshold comparison circuit 500;

[0036] The first voltage divider circuit 100 is used to detect the input voltage at the VIN terminal and divide the voltage to generate a negative input voltage AVIN;

[0037] A starting current generating circuit 200, used to generate a starting current;

[0038] The anti-backflow circuit 300 is used to generate a mirror current and block the backflow current flowing from the VDD terminal to the VIN terminal;

[0039] The second voltage divider circuit 400 is used to detect the output voltage of the VDD terminal and divide the voltage to generate a first positive input voltage AVDD1 and a second positive input voltage AVDD2;

[0040] The threshold comparison circuit 500 includes a comparator COMP1 and a comparator COMP2;

[0041] The comparator COMP1 is used to detect whether the first positive input voltage is greater than the reference voltage, and to control the shutdown of the anti-backflow circuit 300 and the startup current generating circuit 200 when it is confirmed that the first positive input voltage is greater than the reference voltage; the comparator COMP2 is used to compare the negative input voltage AVIN and the second positive input voltage AVDD2, and to control the shutdown of the anti-backflow circuit 300 when it is confirmed that the second positive input voltage AVDD2 is greater than the negative input voltage AVIN.

[0042] In this embodiment, the first voltage divider circuit 100 includes a resistor R1 and a resistor R2; one end of the resistor R1 is electrically connected to the VIN terminal, and the second end is electrically connected to one end of the resistor R2 and is also electrically connected to the inverting input terminal of the comparator COMP2, and the second end of the resistor R2 is electrically connected to the GND terminal;

[0043] The startup current generating circuit 200 includes a resistor R3, a diode D1, a switch tube NM3, a switch tube NM1, a switch tube PM1, a reference current source I REF ; One end of the resistor R3 is electrically connected to the VIN end, and the second end is electrically connected to the cathode of the diode D1 and the drain of the switch tube NM3, and is also electrically connected to the gate of the switch tube NM1; the anode of the diode D1 is electrically connected to the source of the switch tube NM3, and is also electrically connected to the GND end; the gate of the switch tube NM3 is electrically connected to the output end of the comparator COMP1 and the input end of the inverter INV1; the source of the switch tube PM1 is electrically connected to the VIN end, the gate and the drain are electrically connected to the drain of the switch tube NM1, and are also electrically connected to the anode of the diode D2 and the gate of the switch tube PM2; the source of the high-voltage NMOS switch tube is electrically connected to the reference current source I REF One end of the reference current source I REF The second end is electrically connected to the GND end;

[0044] The backflow prevention circuit 300 includes a diode D2, a switch tube PM2, a switch tube PM3, resistors R4 and R5, and a switch tube NM2; the cathode of the diode D2 is electrically connected to the VIN terminal, the anode is electrically connected to the gate of the switch tube PM2, and is also electrically connected to the gate and drain of the switch tube PM1 and the drain of the switch tube NM1; the source of the switch tube PM2 is electrically connected to the VIN terminal, and the drain is electrically connected to the drain of the switch tube PM3; the gate of the switch tube PM3 is electrically connected to one end of the resistors R4 and R5, the source is electrically connected to the second end of the resistor R4 and one end of the resistor R6, and is also electrically connected to the VDD output terminal; the second end of the resistor R5 is electrically connected to the drain of the switch tube NM2; the gate of the switch tube NM2 is electrically connected to the output end of the AND gate AND, and the source is electrically connected to the GND terminal;

[0045] The second voltage divider circuit 400 includes a resistor R6, a resistor R7, and a resistor R8; one end of the resistor R6 is electrically connected to one end of the resistor R4 and the source of the switch tube PM3, and is also electrically connected to the VDD output terminal, and the second end is electrically connected to one end of the resistor R7 and the non-inverting input terminal of the comparator COMP1; the second end of the resistor R7 is electrically connected to one end of the resistor R8 and the non-inverting input terminal of the comparator COMP2; the second end of the resistor R8 is electrically connected to the GND terminal;

[0046] The threshold comparison circuit 500 includes comparators COMP1 and COMP2, inverters INV1 and INV2, and an AND gate AND; the non-inverting input terminal of the comparator COMP1 is electrically connected to one end of the resistor R6 and the resistor R7, and the inverting input terminal is electrically connected to the reference voltage V REF The comparator COMP2 is electrically connected to the input end of the inverter INV1, and its output end is electrically connected to the input end of the inverter INV1; the output end of the inverter INV1 is electrically connected to one end of the AND gate AND; the non-inverting input end of the comparator COMP2 is electrically connected to one end of the resistor R7 and the resistor R8, the inverting input end is electrically connected to one end of the resistor R1 and the resistor R2, and the output end is electrically connected to the input end of the inverter INV2; the output end of the inverter INV2 is electrically connected to the second end of the AND gate AND; the output end of the AND gate AND is electrically connected to the gate of the switch tube NM2.

[0047] The working principle of this embodiment is:

[0048] When the startup circuit is just powered on, the voltage at the VDD terminal is low. At this time, the comparator is enabled and the default output is low. Then xEN is low, VDDOVP is high, and the switch NM2 is turned on. As the VIN voltage rises, V DZ The voltage follows the rise, when V DZ Greater than the threshold voltage V of the switch tube NM1 TH When NM1 is turned on, I REFThe current generates a startup current through the mirror effect of current mirrors PM1 and PM2, and starts to charge the VDD terminal. The VDD voltage gradually rises, and comparators COMP1 and COMP2 are disabled and start to work normally.

[0049] When VIN>VDD, and VDD does not exceed the voltage threshold, the output signal xEN of comparator COMP1 is low, and the output signal of comparator COMP2 is high, then the VDDOVP signal is high, the startup circuit works normally, the anti-backflow tube PM3 is turned on, and V GS =VDD*R5 / (R4+R5), the startup current continues to charge the VDD port; when VIN>VDD, and VDD exceeds the voltage threshold, the output signal xEN of comparator COMP1 is high, the output signal of comparator COMP2 is high, then the VDDOVP signal is low, the switch tube NM1 is turned on, V DZ is pulled down to GND, the switch tube NM2 is turned off, the anti-backflow tube PM3 is turned off, and V GS =VDD, the startup circuit is closed, there is no startup current, and the VDD terminal is powered by the peripheral winding. At this time, if the VDD voltage is greater than the VIN voltage, the parasitic diode will block the backflow current from the VDD terminal to the VIN terminal.

[0050] When the VIN voltage is lower than the VDD overvoltage threshold, at the initial power-on stage, the startup circuit works normally, and there is still startup current charging the VDD terminal. The VDD voltage gradually rises to near the VIN voltage, the comparator COMP1 output signal xEN is low, and the comparator COMP2 output signal is high. Then the VDDOVP signal is low, the anti-backflow tube PM3 is turned off, VGS = VDD, and the parasitic diode blocks the backflow current from the VDD terminal to the VIN terminal. The maximum VDD voltage is equal to VIN.

[0051] The conventional high voltage startup circuit and the high voltage startup circuit of the present embodiment are designed and simulated using DB HiTek 0.18um 100V process. In the DC simulation diagram, Ivdd_vin represents the reverse current from the VDD terminal to the VIN terminal, and Ivin_vdd represents the startup current from the VIN terminal to the VDD terminal.

[0052] Figure 3 The figure shows the simulated waveform of the reverse current from the VDD end to the VIN end of the traditional high-voltage startup circuit under the conditions of VIN = 9V, VDD = 9 ~ 25V. When VDD < VIN and does not exceed the voltage threshold of 9.96V, the maximum reverse current from the VDD end to the VIN end can reach 66.416mA; Figure 4The figure shows the simulation waveform of the reverse current from the VDD terminal to the VIN terminal under the condition of VIN=9V, VDD=9-25V in the embodiment of the present invention. When VDD<VIN and does not exceed the voltage threshold of 9.96V, the maximum reverse current from the VDD terminal to the VIN terminal is only 114.8pA. Figure 5 The figure shows the simulation waveform of the startup current from VIN to VDD under the condition of VIN=9-100V and VDD=8V in the embodiment of the present invention, and the high-voltage startup function is normal; Figure 6 The figure shows the simulation waveform of the startup current from VIN to VDD under the conditions of VIN=9-100V and VDD=12V in the embodiment of the present invention. When VDD<VIN and exceeds the voltage threshold, the startup circuit is closed and the maximum startup current from VIN to VDD is only 284.2pA.

[0053] It can be seen from the simulation results that the high-voltage circuit of the embodiment of the present invention can normally realize the high-voltage startup function under the state of VIN>VDD, and compared with the traditional high-voltage startup circuit, when VIN<VDD and VDD does not exceed the voltage threshold, the problem of backflow of current from the VDD end to the VIN end can be solved.

[0054] The above are only preferred embodiments of the present invention. It should be pointed out that the above preferred embodiments should not be regarded as limitations of the present invention. For ordinary technicians in this technical field, several equivalent substitutions, improvements and modifications can be made without departing from the spirit and scope of the present invention. These equivalent substitutions, improvements and modifications should also be regarded as the protection scope of the present invention. The embodiments will not be repeated here. The protection scope of the present invention should be based on the scope defined by the claims.

Claims

1. A high voltage startup circuit for preventing backflow, characterized in that: The anti-backflow high-voltage startup circuit comprises a first voltage-dividing circuit, a startup current generating circuit, an anti-backflow circuit, a second voltage-dividing circuit and a threshold comparison circuit; The first voltage divider circuit is used to detect the input voltage at the VIN terminal and divide the voltage to generate a negative input voltage AVIN; the startup current generating circuit is used to generate a startup current; The anti-backflow circuit is used to generate a mirror current and block the backflow current flowing from the VDD terminal to the VIN terminal; the second voltage divider circuit is used to detect the output voltage of the VDD terminal and divide the voltage to generate a first positive input voltage AVDD1 and a second positive input voltage AVDD2; The threshold comparison circuit includes a comparator COMP1 and a comparator COMP2; The comparator COMP1 is used to detect whether the first forward input voltage is greater than a reference voltage, and control the shutdown of the anti-backflow circuit and the startup current generating circuit when it is confirmed that the first forward input voltage is greater than the reference voltage; The comparator COMP2 is used for comparing the negative input voltage AVIN with the second positive input voltage AVDD2, and controlling the anti-backflow circuit to be turned off when it is confirmed that the second positive input voltage AVDD2 is greater than the negative input voltage AVIN.

2. The anti-backflow high-voltage starting circuit according to claim 1, characterized in that: The first voltage divider circuit includes a resistor R1 and a resistor R2, the first end of the resistor R1 is connected to the VIN end, the second end of the resistor R1 is connected to the first end of the resistor R2, the second end of the resistor R2 is connected to the ground end, and the output point of the negative input voltage AVIN is the connection point between the resistor R1 and the resistor R2.

3. The anti-backflow high-voltage starting circuit according to claim 1, characterized in that: The startup current generating circuit includes a resistor R3, a diode D1, a switch tube NM3, a switch tube NM1, a switch tube PM1 and a reference current source I REF The gate of the switch tube NM3 is connected to the enable signal xEN to control the on and off of the switch tube NM3; When the enable signal xEN is at a high level, the switch tube NM3 is turned off, and the startup current generating circuit does not work; When the enable signal xEN is at a low level, the switch tube NM3 is turned on, and the startup current generating circuit works.

4. The anti-backflow high-voltage starting circuit according to claim 1, characterized in that: The anti-backflow circuit includes a diode D2, a switch tube PM2, a switch tube PM3, a resistor R4, a resistor R5 and a switch tube NM2; the gate of the switch tube NM2 is connected to an enable signal VDDOVP to control the on and off of the switch tube NM2; when the enable signal VDDOVP is at a high level, the switch tube NM2 is turned on, so that the switch tube PM3 is turned on, and the startup current flows from the VIN terminal to the VDD terminal; When the enable signal VDDOVP is at a low level, the switch tube NM2 is turned off, so that the switch tube PM3 is turned off, thereby blocking the backflow current from the VDD terminal to the VIN terminal.

5. The anti-backflow high-voltage starting circuit according to claim 1, characterized in that: The second voltage divider circuit includes resistors R6, R7 and R8, the first end of the resistor R6 is connected to the VDD end, the second end of the resistor R6 is connected to the ground end through the resistors R7 and R8 in sequence, the output point of the first positive input voltage is the connection point between the resistors R6 and R7, and the output point of the second positive input voltage is the connection point between the resistors R7 and R8.

6. The anti-backflow high-voltage starting circuit according to claim 3, characterized in that: One end of the resistor R3 is electrically connected to the VIN terminal, the second end of the resistor R3 is respectively connected to the cathode of the diode D1, the drain of the switch tube NM3 and the gate of the switch tube NM1, the anode of the diode D1 is electrically connected to the source of the switch tube NM3 and the GND terminal, and the gate of the switch tube NM3 is connected to the enable signal xEN; the source of the switch tube PM1 is electrically connected to the VIN terminal, the gate and drain of the switch tube PM1 are both connected to the anti-backflow circuit, and the source of the switch tube NM1 is connected to the reference current source I REF One end of the reference current source I REF The second end is electrically connected to the GND end.

7. The anti-backflow high-voltage starting circuit according to claim 4, characterized in that: The cathode of the diode D2 is electrically connected to the VIN terminal, and the anode of the diode D2 is connected to the gate of the switch tube PM2 and the startup current generating circuit; the source of the switch tube PM2 is electrically connected to the VIN terminal, the drain of the switch tube PM2 is electrically connected to the drain of the switch tube PM3, the gate of the switch tube PM3 is electrically connected to the first end of the resistor R4 and the first end of R5 respectively, the source of the switch tube PM3 is connected to the second end of the resistor R4 and the VDD terminal, the second end of the resistor R5 is electrically connected to the drain of the switch tube NM2, the gate of the switch tube NM2 is connected to the enable signal VDDOVP, and the source of the switch tube NM2 is electrically connected to the GND terminal.

8. The anti-backflow high-voltage starting circuit according to claim 1, characterized in that: The threshold comparison circuit further includes an inverter INV1, an inverter INV2 and an AND gate AND. The non-inverting input terminal of the comparator COMP1 is connected to the first positive input voltage AVDD1, and the inverting input terminal of the comparator COMP1 is connected to the reference voltage V REF , the output end of the comparator COMP1 is electrically connected to the input end of the inverter INV1; The output end of the inverter INV1 is electrically connected to the first end of the AND gate AND; the non-inverting input end of the comparator COMP2 is connected to the second positive input voltage AVDD2, the inverting input end of the comparator COMP2 is connected to the negative input voltage AVIN, the output end of the comparator COMP2 is electrically connected to the input end of the inverter INV2, the output end of the inverter INV2 is electrically connected to the second end of the AND gate AND, and the output end of the AND gate AND outputs an enable signal VDDOVP.

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