A protection circuit

Abstract

The application discloses a protection circuit, comprising: a first transistor, the first transistor comprising a first end, a second end and a third end, the third end being grounded; a compensation module, the compensation module comprising a first compensation output end, a second compensation output end, a first compensation input end and a second compensation input end, the first compensation input end being connected with VDD, the second compensation input end receiving a voltage signal, and the first compensation output end being connected with the first end; and a shutdown module, the shutdown module comprising a first shutdown input end, a second shutdown input end, a third shutdown input end and a first shutdown output end, the first shutdown input end being connected with the compensation module, the second shutdown input end and the third shutdown input end being connected with the second compensation output end, and the first shutdown output end being connected with the second end. According to the application, the current of the first transistor can be kept constant at a fixed value through the compensation module, and the overcurrent degree of the first transistor can be judged through the shutdown module, so that the first transistor can be turned off by using different currents to protect the first transistor.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to the technical field of circuit protection, in particular to a protection circuit. BACKGROUND

[0002] Functional safety chip has a wide application prospect in new energy vehicles and intelligentization of ordinary vehicles. Many motor drives related to life safety on the vehicle need to have functional safety guarantee. Compared with ordinary vehicle chip, functional safety chip has more stringent requirements for protection of IGBT or SIC. DESAT protection is a common IGBT overcurrent protection method, which detects the VCE voltage of IGBT in the start-up stage, and compares the voltage after a certain filtering with the internal reference voltage. If the voltage exceeds the reference voltage, it is judged that IGBT exits the saturation region, i.e. Desaturation, abbreviated as DESAT, indicating that IGBT overflows, and IGBT needs to be closed to protect IGBT. However, the prior art cannot determine the speed of closing IGBT according to DESAT voltage, so that the chip cannot provide effective protection when the current is rapidly overflowing. SUMMARY

[0003] Embodiments of the present application provide a protection circuit to solve the technical problem that the prior art cannot effectively protect IGBT according to DESAT voltage.

[0004] To solve the above technical problems, embodiments of the present application disclose the following technical solutions:

[0005] The embodiments of the present application provide a protection circuit, comprising:

[0006] A first transistor, the first transistor comprising a first end, a second end and a third end, the third end being grounded;

[0007] A compensation module, the compensation module comprising a first compensation output end, a second compensation output end, a first compensation input end and a second compensation input end, the first compensation input end being connected to VDD, the second compensation input end receiving a voltage signal, the first compensation output end being connected to the first end;

[0008] A shutdown module, the shutdown module comprising a first shutdown input end, a second shutdown input end, a third shutdown input end and a first shutdown output end, the first shutdown input end being connected to the compensation module, the second shutdown input end and the third shutdown input end being connected to the second compensation output end, the first shutdown output end being connected to the second end.

[0009] Further, the compensation module comprises an operational amplifier, a second transistor, a first low-voltage tube and a second low-voltage tube;

[0010] The operational amplifier comprises a first positive power supply end, a first negative power supply end, an enable end and an operation output end, the enable end receives a modulation signal; the operation output end is connected to the gate of the second transistor, the first negative power supply end is connected to the source of the second transistor; the gate of the second low-voltage tube is connected to the modulation signal, the source of the second low-voltage tube is connected to the drain of the second transistor; the source of the first low-voltage tube is connected to the source of the second transistor, and the gate of the first low-voltage tube receives the modulation signal.

[0011] Further, the compensation module further comprises a first high-voltage transistor, a second high-voltage transistor and a first diode, the gate of the first high-voltage transistor is a first compensation input end, the collector of the first high-voltage transistor is a first compensation output end, the gate of the second high-voltage transistor is connected to a working voltage, the cathode of the first diode is connected to the first positive power supply end, and the anode of the first diode is grounded.

[0012] Further, the shutdown module comprises a controller, a third low-voltage tube, a third transistor and a fourth transistor.

[0013] The controller comprises a first control input end, a second control input end, a first control output end and a second control output end, the second control output end is connected to the gate of the third low-voltage tube, the first control input end is connected to the second compensation output end, the drain of the fourth transistor and the gate of the third transistor, the gate of the third transistor is connected to the gate of the fourth transistor; the sources of the third transistor and the fourth transistor are both grounded.

[0014] Further, the protection circuit further comprises an adjustment module, the adjustment module is connected to the compensation module and the shutdown module, the adjustment module comprises a first field effect tube, a second field effect tube, a third field effect tube, a fourth field effect tube and a fifth field effect tube.

[0015] The sources of the first field effect tube, the second field effect tube, the third field effect tube, the fourth field effect tube and the fifth field effect tube are commonly connected, the gate of the first field effect tube is connected to the gate of the second field effect tube, the drain and the gate of the first field effect tube are connected to the drain of the first low-voltage tube, the drain of the second field effect tube is connected to the emitter of the first high-voltage transistor and the drain of the third field effect tube, the drain of the fourth field effect tube is connected to the gate of the third field effect tube and the drain of the second low-voltage tube, the drain of the fifth field effect tube is connected to the emitter of the second high-voltage transistor, and the collector of the second high-voltage transistor is connected to the drain of the fourth transistor and the gate of the fourth transistor respectively.

[0016] Further, the protection circuit further comprises a conversion module connected between the compensation module and the shutdown module, the conversion module comprising a comparator, an RS flip-flop and a converter.

[0017] The enable end of the comparator is connected with the modulation signal, the positive power supply end of the comparator is connected with the first compensation output end, and the negative power supply end of the comparator is grounded; the S end of the RS flip-flop is connected with the output end of the comparator, the R end of the RS flip-flop is connected with the modulation signal, and the Q end of the RS flip-flop is connected with the converter.

[0018] Further, the compensation module further comprises a first current source and a first resistor, the first current source is connected with the first resistor in series, the first current source is connected with the source of the first low-voltage tube, and the first resistor is connected with the source of the second transistor.

[0019] Further, the compensation module further comprises a second resistor and a third resistor; one end of the second resistor is grounded, the other end of the second resistor is connected with one end of the third resistor, the first positive power supply end and the positive power supply end of the comparator; the other end of the third resistor is connected with the collector of the first high-voltage transistor.

[0020] Further, the conversion module further comprises a reference voltage source, and the positive electrode of the reference voltage source is connected with the negative power supply end of the comparator.

[0021] Further, the adjustment module further comprises a second current source, one end of the second current source is connected with a power supply voltage, and the other end of the second current source is connected with the third transistor and the second control input end respectively.

[0022] Further, the protection circuit further comprises a second diode, a fourth resistor and a capacitor.

[0023] The cathode of the second diode is connected with the first end, the anode of the second diode is connected with the collector of the first high-voltage transistor, one end of the capacitor is connected with the first end, and the other end of the capacitor is grounded; one end of the fourth resistor is connected with the second end, and the other end of the fourth resistor is connected with the collector of the third low-voltage tube.

[0024] One of the above technical solutions has the following advantages or beneficial effects:

[0025] Compared with the prior art, the embodiment of the application provides a protection circuit, which comprises a first transistor, the first transistor comprising a first end, a second end and a third end, the third end being grounded; a compensation module, the compensation module comprising a first compensation output end, a second compensation output end, a first compensation input end and a second compensation input end, the first compensation input end being connected with VDD, the second compensation input end receiving a voltage signal, and the first compensation output end being connected with the first end; and a turn-off module, the turn-off module comprising a first turn-off input end, a second turn-off input end, a third turn-off input end and a first turn-off output end, the first turn-off input end being connected with the compensation module, the second turn-off input end and the third turn-off input end being connected with the second compensation output end, and the first turn-off output end being connected with the second end. The compensation module can make the current output by the circuit not change with the voltage, so that the current of the first transistor is constant at a fixed value. Meanwhile, the turn-off module can determine the overcurrent degree of the first transistor and adopt different currents to turn off the first transistor, so as to protect the first transistor. BRIEF DESCRIPTION OF DRAWINGS

[0026] The technical scheme and other beneficial effects of the application will be apparent from the following detailed description of the specific embodiments of the application in combination with the drawings.

[0027] Figure 1 The circuit structure schematic diagram provided by the embodiment of the application is shown in the following.

[0028] The reference signs are as follows:

[0029] 1-first high-voltage triode, 2-first low-voltage tube, 3-second low-voltage tube, 4-operational amplifier, 5-comparator, 6-RS flip-flop, 7-converter, 8-controller, 9-third low-voltage tube, 10-first current source, 11-reference voltage source, 12-second current source, 13-third transistor, 14-fourth transistor, 15-first transistor, 16-second transistor, 17-first field effect tube, 18-second field effect tube, 19-third field effect tube, 20-fourth field effect tube, 21-fifth field effect tube, 22-second high-voltage triode, D1-first diode, D2-second diode, R1-first resistor, R2-second resistor, R3-third resistor, R4-fourth resistor, A1-compensation module, A2-conversion module, A3-turn-off module, A4-regulation module. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described in the description of the embodiments of the present application in combination with the drawings in the embodiments of the present application. In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features limited by "first", "second" can be explicitly or implicitly included one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise specifically limited.

[0031] Applicants note that some existing product solutions, such as isolation drive chips such as ucc21750 and NSD6611, charge the DESAT PIN through a current mirror, and the accuracy is related to the DESAT voltage and the DESAT threshold voltage. When the IGBT used in the chip is turned on, it is generally in the saturation region, i.e. the VCE voltage is less than the VBE voltage. If the IGBT current is too large, the VCE voltage will be greater than the VBE voltage, and the IGBT will exit the saturation region and enter the amplification region, i.e. DESAT. At this time, the VCE voltage of the IGBT will rise sharply, which may cause overheating damage. The DESAT charging current generally varies with the DESAT voltage. If there are multiple gears for DESAT, the current will also vary nonlinearly with each gear, making it difficult to predict the DESAT protection time. For example, the DESAT charging current I DEAT0 = 200uA, and the divided voltage is generally small in order to reduce the delay, such as 50K. When the DESAT voltage is 1V, the current flowing through the voltage dividing resistor is 20uA; when the DESAT voltage is 6V, the current flowing through the voltage dividing resistor is 120uA, and the actual charging current I DEAT1 = I DESAT0 -IRdiv = 80uA-180uA, with a large deviation. At the same time, the prior art cannot determine the speed of turning off the IGBT according to the DESAT voltage, so that the chip cannot provide effective protection when the current is rapidly overcurrent.

[0032] The specific implementation of the present application will be described below by way of examples:

[0033] Please refer toFigure 1 The embodiment of the application provides a protection circuit, which comprises a first transistor 15, a compensation module A1, a conversion module A2, an off module A3, an adjustment module A4, a second diode D2, a fourth resistor R4 and a capacitor C out ; wherein the first transistor 15 comprises a first end, a second end and a third end, the first end is a collector end, the second end is a gate end, the third end is an emitter end, and the emitter end is grounded; the compensation module A1 comprises a first compensation output end, a second compensation output end, a first compensation input end and a second compensation input end, the first compensation input end is connected with VDD, the second compensation input end receives a voltage signal, and the first compensation output end is connected with the first end, that is, the collector end; the off module A3 comprises a first off input end, a second off input end, a third off input end and a first off output end, the first off input end is connected with the compensation module A1, the second off input end and the third off input end are connected with the second compensation output end, and the first off output end is connected with the second end, that is, the gate end. It can be understood that the first transistor 15 is an IGBT in the application, the IGBT is the abbreviation of Insulated Gate Bipolar Transistor, the Chinese name is an insulated gate bipolar transistor, which is a composite full-controlled voltage drive power semiconductor device composed of a bipolar junction transistor (BJT) and an insulated gate type field effect transistor (MOS), the driving power of the TGBT is small and the saturation voltage drop is low, and the TGBT is suitable for fields such as alternating current motors, frequency converters, switching power supplies, lighting circuits and traction transmission. The application compensates the DESAT current in real time through the compensation module A1, solves the problem that the DESAT current precision changes with different gear positions and different VCE voltages of the IGBT, and simultaneously through the off module A3, different SSD currents can be used to turn off the IGBT with different overcurrent degrees of the IGBT.

[0034] In the embodiment of the application, the compensation module A1 comprises an operational amplifier 4, a second transistor 16, a first low-voltage tube 2, a second low-voltage tube 3, a first high-voltage triode 1, a second high-voltage triode 22, a first diode D1, a first current source 10, a first resistor R1, a second resistor R2 and a third resistor R3.

[0035] The operation amplifier 4 includes a first positive power supply end, a first negative power supply end, an enable end and an operation output end, the enable end receives a modulation signal, the operation output end is connected to the gate of the second transistor 16, the first negative power supply end is connected to the source of the second transistor 16, the gate of the second low-voltage tube 3 is connected to the modulation signal, the source of the second low-voltage tube 3 is connected to the drain of the second transistor 16, the source of the first low-voltage tube 2 is connected to the source of the second transistor 16, the gate of the first low-voltage tube 2 receives the modulation signal, the gate of the first high-voltage transistor 1 is the first compensation input end, the first compensation input end is connected to VDD, the input voltage of VDD is 5V, the collector of the first high-voltage transistor 1 is the first compensation output end, the cathode of the first diode D1 is connected to the first positive power supply end, and the anode of the first diode D1 is grounded, the gate of the second high-voltage transistor 22 is connected to the working voltage VCC, and the working voltage VCC is 5V, the first current source 10 is connected to the source of the first low-voltage tube 2 in series with the first resistor R1, the first resistor R1 is connected to the source of the second transistor 16, one end of the second resistor R2 is grounded, the other end of the second resistor is connected to one end of the third resistor R3, the first positive power supply end and the positive power supply end of the comparator 5, the other end of the third resistor R3 is connected to the collector of the first high-voltage transistor 1, and the resistance value of the first resistor R1 is equal to the resistance value of the second resistor R2. It can be understood that the operation amplifier 4 can sample the voltage on the second resistor R2 and add the obtained voltage to the first resistor R1, so that the currents flowing through the first resistor R1 and the second resistor R2 are equal. The modulation signal in the application is a PWM signal, which provides a periodic signal for a chip or a transistor. In some other embodiments, the modulation signal can also be other types of modulation signals. In the embodiment of the application, the first current source 10 is a bias current source Ibias0, the second transistor 16 is an NMOS transistor, the first low-voltage tube 2 is an N-type LDMOS transistor, the second low-voltage tube 3 is an N-type LDMOS transistor, and the first high-voltage transistor 1 and the second high-voltage transistor 22 are both P-type LDMOS transistors.

[0036] In the embodiment of the application, the turn-off module A3 includes a controller 8, a third low-voltage tube 9, a third transistor 13 and a fourth transistor 14, the controller 8 includes a first control input end, a second control input end, a first control output end and a second control output end, the second control output end is connected to the gate of the third low-voltage tube 9, the first control input end is connected to the second compensation output end, the drain of the fourth transistor 14 and the gate of the third transistor 13, the gate of the third transistor 13 is connected to the gate of the fourth transistor 14, and the sources of the third transistor 13 and the fourth transistor 14 are both grounded. In the embodiment of the application, the controller 8 can include; the third low-voltage tube 9 is an N-type LDMOS transistor, the third transistor 13 is an NMOS transistor, and the fourth transistor 14 is an NMOS transistor.

[0037] In the embodiment of the present application, the adjusting module A4 is connected with the compensation module A1 and the turn-off module A3, the adjusting module A4 comprises a first field effect tube 17, a second field effect tube 18, a third field effect tube 19, a fourth field effect tube 20, a fifth field effect tube 21 and a second current source 12; the sources of the first field effect tube 17, the second field effect tube 18, the third field effect tube 19, the fourth field effect tube 20 and the fifth field effect tube 21 are commonly connected, the gate of the first field effect tube 17 is connected with the gate of the second field effect tube 18, the drain and the gate of the first field effect tube 17 are connected with the drain of the first low-voltage tube 2, the drain of the second field effect tube 18 is connected with the emitter of the first high-voltage triode 1 and the drain of the third field effect tube 19, the drain of the fourth field effect tube 20 is connected with the gate of the third field effect tube 19 and the drain of the second low-voltage tube 3, the drain of the fifth field effect tube 21 is connected with the emitter of the second high-voltage triode 22, the collector of the second high-voltage triode 22 is connected with the drain of the fourth transistor 14 and the gate of the fourth transistor 14 respectively; one end of the second current source 12 is connected with a power supply voltage, the other end of the second current source 12 is connected with the third transistor 13 and the second control input end respectively. In the embodiment of the present application, the first field effect tube 17 is a PMOS transistor; the second field effect tube 18 is a PMOS transistor; the third field effect tube 19 is a PMOS transistor; the fourth field effect tube 20 is a PMOS transistor; the fifth field effect tube 21 is a PMOS transistor.

[0038] In the embodiment of the present application, the conversion module A2 is connected between the compensation module A1 and the turn-off module A3, the conversion module A2 comprises a comparator 5, an RS flip-flop 6, a converter 7 and a reference voltage source 11; the enable end of the comparator 5 is connected with a modulation signal, the positive power supply end of the comparator 5 is connected with a first compensation output end, and the negative power supply end of the comparator 5 is grounded; the S end of the RS flip-flop 6 is connected with the output end of the comparator 5, the R end of the RS flip-flop 6 is connected with a modulation signal, and the Q end of the RS flip-flop 6 is connected with a converter; the positive pole of the reference voltage source 11 is connected with the negative power supply end of the comparator 5. In the embodiment of the present application, the comparator 5 comprises a zero-crossing comparator or a voltage comparator; the converter 7 comprises a voltage converter or a level converter, and the main function is to switch the input signal from one voltage domain to another voltage domain.

[0039] In the embodiment of the present application, the cathode of the second diode D2 is connected with the first end, the anode of the second diode D2 is connected with the collector of the first high-voltage triode 1; one end of a capacitor is connected with the first end, and the other end of the capacitor is grounded; one end of a fourth resistor is connected with the second end, and the other end of the fourth resistor is connected with the collector of the third low-voltage tube 9.

[0040] In this application, the converter 7 includes a voltage / level shifter (LS), a fundamental circuit often used in SOC design. Its primary function is to switch the input signal from one voltage domain to another. Different voltage domains have different VDDs, and without voltage conversion, the device will not function properly.

[0041] The working principle of the circuit of the present application includes that after the first transistor 15 is turned on, the first low-voltage tube 2 is turned on, and the first field effect tube 17 copies the reference current I of the first current source 10. bias0 To the second field effect tube 18, the current of the first field effect tube 17 and the second field effect tube 18 satisfies: I 18 / I 17 =K, and at the same time, the operational amplifier 4 samples the voltage on the second resistor R2 and adds it to the first resistor R1 with the same resistance, so that the current I1 flowing through the first resistor R1 is equal to the current I2 flowing through the second resistor R2. The current I1 is mirrored by the fourth field effect transistor 20 and the third field effect transistor 19 and then added to the first high-voltage transistor 1. The current I3 on ​​the first high-voltage transistor 1 = I1 + K·I bias0 The current I2 on the second resistor R2 = V DESAT / (R3+R2), the voltage V2 on the second resistor R2 = V DESAT *R2 / (R3+R2), the current flowing through the second diode D2 is I DESAT =I1+K·I bias0 -I1=K·I bias0 , we can find the current I of the second diode D2 DESAT It has nothing to do with the DESAT current and the first resistor R1. Therefore, the DESAT filtering time is equal to T DESAT =C out VREF (R2+R3) / R2 / I DESAT , and V DESAT Irrelevant T DESAT time.

[0042] Accordingly, the working principle of soft shutdown technology includes, for example Figure 1 As shown, after the operational amplifier 4 converts the DESAT voltage into a current, it copies the current to the fifth field effect transistor 21 through the fourth field effect transistor 20. At this time, an initial SSD current I_SSD0 is set, that is, at V DESAT When it is just equal to the threshold, the soft shutdown current I_SSD1=I SSD0 -V DESATVDESAT continues to increase, I_SSD1 will decrease accordingly until I_SSD1 reaches the minimum current I_SSD1 = I_SSD0 - V zener R2.

[0043] The above has carried out the detailed introduction to the protection circuit provided by the embodiment of the application, the principle and implementation mode of the application are described in this paper, the above embodiment is only used to help understanding the technical scheme of the application and its core idea; The ordinary skilled in the art should understand that: it can still modify the technical scheme recorded by the foregoing embodiments, or make equivalent replacement to part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical scheme deviate from the scope of the technical scheme of the embodiments of the application.

Claims

1. A protection circuit, characterized in that: include: A first transistor (15), the first transistor (15) comprising a first terminal, a second terminal and a third terminal, the third terminal being grounded; a compensation module, the compensation module comprising a first compensation output terminal, a second compensation output terminal, a first compensation input terminal, and a second compensation input terminal, the first compensation input terminal being connected to VDD, the second compensation input terminal receiving a voltage signal, and the first compensation output terminal being connected to the first terminal; The compensation module further comprises a first high-voltage triode (1), the gate of the first high-voltage triode (1) being a first compensation input terminal, and the collector of the first high-voltage triode (1) being a first compensation output terminal; A shutdown module, the shutdown module comprising a first shutdown input terminal, a second shutdown input terminal, a third shutdown input terminal and a first shutdown output terminal, the first shutdown input terminal being connected to the compensation module, the second shutdown input terminal and the third shutdown input terminal being connected to the second compensation output terminal, and the first shutdown output terminal being connected to the second terminal.

2. The protection circuit according to claim 1, wherein: The compensation module comprises an operational amplifier (4), a second transistor (16), a first low-voltage tube (2) and a second low-voltage tube (3); The operational amplifier (4) comprises a first positive power supply terminal, a first negative power supply terminal, an enable terminal and an operational output terminal, wherein the enable terminal receives a modulation signal; the operational output terminal is connected to the gate of the second transistor (16), and the first negative power supply terminal is connected to the source of the second transistor (16); the gate of the second low-voltage tube (3) is connected to the modulation signal, and the source of the second low-voltage tube (3) is connected to the drain of the second transistor (16); the source of the first low-voltage tube (2) is connected to the source of the second transistor (16), and the gate of the first low-voltage tube (2) receives the modulation signal.

3. The protection circuit according to claim 2, wherein: The compensation module further comprises a second high-voltage triode (22) and a first diode, wherein the gate of the second high-voltage triode (22) is connected to the operating voltage, the cathode of the first diode is connected to the first positive power supply terminal, and the anode of the first diode is grounded.

4. The protection circuit according to claim 3, wherein: The shutdown module comprises a controller (8), a third low-voltage tube (9), a third transistor (13) and a fourth transistor (14); The controller (8) comprises a first control input terminal, a second control input terminal, a first control output terminal and a second control output terminal, wherein the second control output terminal is connected to the gate of the third low-voltage tube (9), the first control input terminal is connected to the second compensation output terminal, the drain of the fourth transistor (14) and the gate of the third transistor (13), and the gate of the third transistor (13) is connected to the gate of the fourth transistor (14); and the sources of the third transistor (13) and the fourth transistor (14) are both grounded.

5. The protection circuit according to claim 4, wherein: The protection circuit further comprises a regulating module, the regulating module being connected to the compensation module and the shut-down module, the regulating module comprising a first field effect transistor (17), a second field effect transistor (18), a third field effect transistor (19), a fourth field effect transistor (20) and a fifth field effect transistor (21); The sources of the first field effect transistor (17), the second field effect transistor (18), the third field effect transistor (19), the fourth field effect transistor (20) and the fifth field effect transistor (21) are connected in common; the gate of the first field effect transistor (17) is connected to the gate of the second field effect transistor (18); the drain and gate of the first field effect transistor (17) are connected to the drain of the first low-voltage transistor (2); the drain of the second field effect transistor (18) is connected to the emitter of the first high-voltage transistor (1) and the drain of the third field effect transistor (19); the drain of the fourth field effect transistor (20) is connected to the gate of the third field effect transistor (19) and the drain of the second low-voltage transistor (3); the drain of the fifth field effect transistor (21) is connected to the emitter of the second high-voltage transistor (22); and the collector of the second high-voltage transistor (22) is connected to the drain of the fourth transistor (14) and the gate of the fourth transistor (14) respectively.

6. The protection circuit according to claim 3, wherein: The protection circuit further comprises a conversion module, the conversion module being connected between the compensation module and the shutdown module, the conversion module comprising a comparator (5), an RS trigger (6) and a converter (7); The enable terminal of the comparator (5) is connected to the modulation signal, the positive power supply terminal of the comparator (5) is connected to the first compensation output terminal, and the negative power supply terminal of the comparator (5) is grounded; the S terminal of the RS trigger (6) is connected to the output terminal of the comparator (5), the R terminal of the RS trigger (6) is connected to the modulation signal, and the Q terminal of the RS trigger (6) is connected to the converter (7).

7. The protection circuit according to claim 3, wherein: The compensation module further comprises a first current source (10) and a first resistor, wherein the first current source (10) is connected in series with the first resistor, the first current source (10) is connected to the source of the first low-voltage tube (2), and the first resistor is connected to the source of the second transistor (16).

8. The protection circuit according to claim 6, wherein: The compensation module further includes a second resistor and a third resistor; one end of the second resistor is grounded, and the other end of the second resistor is connected to one end of the third resistor, the first positive power supply end, and the positive power supply end of the comparator (5); the other end of the third resistor is connected to the collector of the first high-voltage transistor (1).

9. The protection circuit according to claim 6, wherein: The conversion module further comprises a reference voltage source (11), the positive electrode of the reference voltage source (11) being connected to the negative power supply terminal of the comparator (5).

10. The protection circuit according to claim 5, wherein: The regulating module further comprises a second current source (12), one end of the second current source (12) is connected to the power supply voltage, and the other end of the second current source (12) is respectively connected to the third transistor (13) and the second control input end.

11. The protection circuit according to claim 4, wherein: The protection circuit further includes a second diode, a fourth resistor and a capacitor; The cathode of the second diode is connected to the first end, and the anode of the second diode is connected to the collector of the first high-voltage transistor (1); one end of the capacitor is connected to the first end, and the other end of the capacitor is grounded; one end of the fourth resistor is connected to the second end, and the other end of the fourth resistor is connected to the collector of the third low-voltage transistor (9).

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