Linear voltage regulator circuit

Abstract

The embodiment of the invention provides a linear voltage regulator circuit, and relates to the technical field of linear voltage regulators. The linear voltage regulator circuit comprises a first MOS tube, a negative feedback loop, a grid turn-off circuit and an overvoltage bleeder circuit. The grid turn-off circuit is used for turning off the first MOS tube when the alternating current component of the first voltage is greater than a first set value; the overvoltage bleeder circuit is used for enabling a part of charges of the drain electrode of the first MOS tube to be released to the ground when the output voltage of the drain electrode of the first MOS tube is too high, the problem that overvoltage is generated by output due to input voltage disturbance is solved, and direct-current voltage-stabilized output is achieved.

Description

Technical Field

[0001] The present application relates to the technical field of linear voltage regulators, and in particular to a linear voltage regulator circuit. Background Art

[0002] Linear regulators often use a larger MOS tube to connect the input and output, and adjust the output voltage by controlling the gate voltage of the MOS tube.

[0003] In normal operation, both the input and output voltages are DC. However, in some scenarios, the input voltage may be disturbed and superimposed with a high-frequency AC signal, which is partially coupled to the gate of the MOS tube through parasitic capacitance. However, since this node has parasitic capacitance to other nodes (such as capacitance to ground), a voltage divider effect is generated, so the driving voltage of the MOS tube will change, causing the output voltage to float higher.

[0004] Therefore, an input disturbance protection circuit is required in the system to deal with such situations.

[0005] How to design an input disturbance protection circuit for the MOS tube of a linear regulator is a technical problem to be solved by this application. Summary of the invention

[0006] The purpose of the present application is to provide a linear regulator circuit to solve the technical problem of how to design an input disturbance protection circuit for a MOS tube of a linear regulator in the prior art.

[0007] To achieve the above objectives, the embodiments of the present application adopt the following technical solutions.

[0008] The embodiment of the present application provides a linear regulator circuit, including a first MOS tube, a negative feedback loop, a gate shutdown circuit and an overvoltage discharge circuit;

[0009] The source of the first MOS tube is used to receive a first voltage, the drain of the first MOS tube is used to output a second voltage, the drain of the first MOS tube is connected to the first end of the overvoltage discharge circuit and the first end of the negative feedback loop; the second end of the negative feedback loop is connected to the gate of the first MOS tube; the second end of the overvoltage discharge circuit is grounded;

[0010] The gate shutoff circuit is connected between the gate and the source of the first MOS tube; the gate shutoff circuit is used to generate a third voltage when the AC component of the first voltage is greater than a first set value, and the third voltage shuts off the first MOS tube;

[0011] The overvoltage discharge circuit is used to release a part of the charge of the drain of the first MOS tube to the ground when the second voltage reaches a second set value.

[0012] Optionally, the overvoltage discharge circuit includes a comparison module, a switch module and a ground current limiting module;

[0013] The comparison module is used for outputting a signal to turn on the switch module when the second voltage reaches a second set value;

[0014] When the switch module is turned on, a portion of the charge at the drain of the first MOS tube passes through the ground current limiting module to the ground.

[0015] Optionally, the linear regulator circuit further includes a voltage-dividing resistor unit; the drain of the first MOS tube is connected to the first end of the overvoltage discharge circuit through the voltage-dividing resistor unit.

[0016] Optionally, the comparison module includes a comparator;

[0017] The first end of the voltage-dividing resistor unit is connected to the drain of the first MOS tube, the second end of the voltage-dividing resistor unit is grounded, and the third end of the voltage-dividing resistor unit is connected to the first input end of the comparator;

[0018] The second input terminal of the comparator is used to receive a first reference voltage;

[0019] The output end of the comparator is connected to the control end of the switch module.

[0020] Optionally, the comparison module further includes an offset voltage adjustment unit, the second input terminal of the comparator is connected to the first terminal of the offset voltage adjustment unit, and the second terminal of the offset voltage adjustment unit is used to receive the first reference voltage.

[0021] Optionally, the voltage-dividing resistor unit includes a first resistor unit and a second resistor unit;

[0022] The first end of the first resistor unit is connected to the drain of the first MOS tube;

[0023] The second end of the first resistance unit is connected to the second end of the second resistance unit and the first input end of the comparator;

[0024] A second terminal of the second resistance unit is grounded.

[0025] Optionally, the ground current limiting module includes a current source or a resistance module.

[0026] Optionally, the gate shutoff circuit includes a switch tube and an AC voltage generating module;

[0027] The first end of the AC voltage generating module is used to receive the first voltage;

[0028] The second end of the AC voltage generating module is connected to the control end of the switch tube;

[0029] The third terminal of the AC voltage generating module is grounded;

[0030] The first end of the switch tube and the second end of the switch tube are connected between the gate and the source of the first MOS tube; the first MOS tube is an enhancement type PMOS tube.

[0031] Optionally, the AC voltage generating module includes a third resistance unit, a fourth resistance unit and a capacitor;

[0032] The first end of the third resistor unit is used to receive the first voltage;

[0033] The second end of the third resistor unit is connected to the first end of the fourth resistor unit;

[0034] The second end of the fourth resistor unit is connected to the first end of the capacitor;

[0035] The second terminal of the capacitor is grounded.

[0036] Optionally, the negative feedback loop includes an operational amplifier; the linear regulator circuit also includes a voltage divider resistor unit;

[0037] The first end of the first resistor unit is connected to the drain of the first MOS tube;

[0038] The second end of the first resistance unit is connected to the second end of the second resistance unit and the first input end of the operational amplifier;

[0039] The second end of the second resistance unit is grounded;

[0040] The second input terminal of the operational amplifier is used to receive a second reference voltage;

[0041] The output end of the operational amplifier is connected to the gate of the first MOS tube.

[0042] Optionally, the overvoltage relief circuit includes a comparison module, a switch module and a ground current limiting module; the output end of the comparison module is connected to the power supply end of the operational amplifier.

[0043] Compared with the prior art, this application has the following beneficial effects:

[0044] In the linear regulator circuit provided by the embodiment of the present application, when an AC signal of a certain frequency or amplitude appears in the input first voltage, the gate shutoff circuit shuts off the first MOS tube to suppress the possible increase in the output voltage. If the load is too small, simply shutting off the first MOS tube is not enough to suppress the increase in the output voltage. When the output voltage is too high, the overvoltage discharge circuit can also be used to reduce the output voltage, thereby better avoiding affecting the subsequent circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1 A schematic diagram of a linear regulator circuit provided in an embodiment of the present application;

[0047] Figure 2 A schematic diagram of a linear regulator circuit including a MOS tube and an operational amplifier provided in an embodiment of the present application;

[0048] Figure 3 A schematic diagram of a linear voltage regulator circuit including a voltage-dividing resistor unit provided in an embodiment of the present application;

[0049] Figure 4 A schematic diagram of a linear regulator circuit including a gate shutoff circuit provided in an embodiment of the present application;

[0050] Figure 5 A schematic diagram of a linear regulator circuit including a gate shutoff circuit and a voltage dividing resistor unit provided in an embodiment of the present application;

[0051] Figure 6 A schematic diagram of a linear regulator circuit including an overvoltage relief circuit provided in an embodiment of the present application;

[0052] Figure 7 A schematic diagram of a linear regulator circuit including a gate shutdown circuit and an overvoltage discharge circuit provided in an embodiment of the present application;

[0053] Figure 8 A schematic diagram of an overvoltage discharge circuit provided in an embodiment of the present application includes a comparison module, a switch module and a ground current limiting module;

[0054] Fig. 9 for Figure 8 A schematic diagram showing the positions of the switch module and the ground current limiting module being interchanged;

[0055] Fig.10 For Figure 8 The schematic diagram of the linear voltage regulator circuit with a voltage divider resistor unit added to the base;

[0056] Fig.11 A schematic diagram of a comparison module and a negative feedback loop sharing a voltage-dividing resistor unit provided in an embodiment of the present application;

[0057] Fig.12 An overvoltage discharge circuit provided in an embodiment of the present application includes a comparator OV Comp and a current source I1;

[0058] Fig.13 A schematic diagram of an implementation scheme of a gate shutoff circuit provided in an embodiment of the present application, including a switch tube and an AC voltage generating module;

[0059] Fig.14 An AC voltage generating module provided in an embodiment of the present application includes a third resistor unit R1, a fourth resistor unit R2 and a capacitor C1. DETAILED DESCRIPTION

[0060] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. The described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described in the drawings here can be arranged and designed in various different configurations.

[0061] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0062] In the description of this application, it should be noted that:

[0063] Relational terms such as first and second, etc., are used merely to distinguish one entity or operation from another entity or operation, but do not necessarily require or imply any such actual relationship or order between these entities or operations;

[0064] “Connection” 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 direct connection or an indirect connection through an intermediate medium.

[0065] like Figure 1, Figure 1 A linear regulator circuit is shown, including a first MOS tube and a negative feedback loop, wherein the source of the first MOS tube is used to receive an input voltage VIN, the drain of the first MOS tube is used to output an output voltage VOUT, the drain of the first MOS tube is connected to a first end of the negative feedback loop, and the second end of the negative feedback loop is connected to a gate of the first MOS tube.

[0066] like Figure 2 , the negative feedback loop can include an operational amplifier. The operational amplifier has the following connections:

[0067] The drain of the first MOS tube is connected to the first input terminal of the operational amplifier;

[0068] The second input terminal of the operational amplifier is used to receive a reference voltage VREF;

[0069] The output end of the operational amplifier is connected to the gate of the first MOS tube.

[0070] The voltage at the output end of the operational amplifier affects the gate voltage of the first MOS tube, thereby affecting the voltage between the gate and the source of the first MOS tube, thereby achieving negative feedback regulation of the output voltage VOUT output by the first MOS tube.

[0071] like Figure 3 The linear regulator circuit may further include a voltage-dividing resistor unit, and the drain of the first MOS tube is connected to the first input terminal of the operational amplifier through the voltage-dividing resistor unit.

[0072] The voltage-dividing resistor unit includes a first resistor unit R11 and a second resistor unit R12, which have the following connection relationship:

[0073] A first end of the first resistor unit R11 is connected to the drain of the first MOS tube;

[0074] The second end of the first resistance unit R11 is connected to the second end of the second resistance unit R12 and the first input end of the comparator;

[0075] A second end of the second resistance unit R12 is grounded.

[0076] The voltage-dividing resistor unit can provide the output voltage VOUT output by the first MOS tube to the operational amplifier in proportion, so as to better meet the requirements of the operational amplifier and the reference voltage VREF.

[0077] like Figure 4 ,exist Figure 1 A gate turn-off circuit can be added on the basis of the linear regulator circuit, the linear regulator circuit includes a first MOS tube, a negative feedback loop and a gate turn-off circuit. The gate turn-off circuit has the following connection relationship: the gate turn-off circuit is connected between the gate and the source of the first MOS tube.

[0078] The gate turn-off circuit can obtain an input voltage at the source of the first MOS tube. The gate turn-off circuit is used to generate a third voltage between the gate and the source of the first MOS tube when the AC component of the input voltage is greater than a first set value. The third voltage turns off the first MOS tube, thereby suppressing the fluctuation of the output voltage VOUT.

[0079] like Figure 5 Taking the enhancement type PMOS tube as the first MOS tube as an example, the third voltage can be a voltage close to 0, and the gate turn-off circuit can turn on or off the gate and source of the first MOS tube, thereby controlling the on or off state of the first MOS tube.

[0080] Although when the AC component of the input voltage is greater than the first set value, turning off the first MOS tube can suppress the fluctuation of the output voltage VOUT, if the load connected to the output voltage VOUT is too small, the output voltage VOUT still has the problem of not being able to decrease quickly when the output voltage VOUT is large, especially when there is an output capacitor at the output end, the output capacitor forms additional charge. The output voltage VOUT maintains a high value for a long time, affecting the subsequent circuit and even causing the risk of overvoltage burning.

[0081] like Figure 6 , an overvoltage relief circuit can be set at the position of the output voltage VOUT, and the linear regulator circuit includes a first MOS tube, a negative feedback loop and an overvoltage relief circuit. The overvoltage relief circuit has the following connection relationship:

[0082] The drain of the first MOS tube is connected to the first end of the overvoltage discharge circuit;

[0083] The second terminal of the overvoltage discharge circuit is grounded.

[0084] The function set by the overvoltage discharge circuit includes: when the output voltage VOUT reaches a second set value, a part of the charge of the drain of the first MOS tube is released to the ground.

[0085] At this time, when the first MOS tube is turned off, the overvoltage discharge circuit can still quickly reduce the output voltage VOUT of the first MOS tube, avoiding the above-mentioned problem that the output voltage VOUT maintains a high value for a long time even when the first MOS tube is turned off.

[0086] like Figure 7 , you can also Figure 6 On the basis of the overvoltage discharge circuit, the gate shutdown circuit is combined with the overvoltage discharge circuit. At this time, the linear regulator circuit includes a first MOS tube, a negative feedback loop, a gate shutdown circuit and an overvoltage discharge circuit.

[0087] It can be controlled by the gate turn-off circuit at the input end and by the overvoltage relief circuit at the output end. Therefore, the linear regulator circuit combining the gate turn-off circuit with the overvoltage relief circuit has a faster recovery speed of the output voltage VOUT and runs more smoothly.

[0088] like Figure 8 The overvoltage discharge circuit may include a comparison module, a switch module and a ground current limiting module.

[0089] The comparison module has the following functions: when the output voltage VOUT reaches the second set value, the comparison module outputs a signal to turn on the switch module. When the switch module is turned on, a portion of the charge of the drain of the first MOS tube passes through the ground current limiting module to the ground.

[0090] In order to achieve the effect that a part of the charge at the drain of the first MOS tube passes through the grounding current limiting module to the ground when the switch module is turned on, the connection method can be: the first input end of the comparison module is connected to the drain of the first MOS tube to obtain the output voltage VOUT, the second input end of the comparison module receives the reference voltage (this reference voltage can be the same as the reference voltage of the above-mentioned operational amplifier, and can also be different from the reference voltage of the above-mentioned operational amplifier), the output end of the comparison module is connected to the control end of the switch module, the first end of the switch module is connected to the drain of the first MOS tube, the second end of the switch module is connected to the first end of the grounding current limiting module, and the second end of the grounding current limiting module is grounded, that is, Figure 8 Connection method shown.

[0091] Fig. 9 An alternative connection method is shown. The positions of the switch module and the ground current limiting module are interchanged, which can also achieve the effect that when the switch module is turned on, part of the charge of the drain of the first MOS tube passes through the ground current limiting module to the ground. The ground current limiting module can be a current source or a resistor.

[0092] like Fig.10 In order to adapt to the comparison module and the reference voltage connected to the comparison module, a voltage-dividing resistor unit can be provided. The drain of the first MOS tube is connected to the first input terminal of the comparison module through the voltage-dividing resistor unit. Fig.11 The first input terminal of the comparison module can also share a voltage-dividing resistor unit with the negative feedback loop.

[0093] Fig.12 An implementation of an overvoltage discharge circuit including a comparator OV Comp and a current source I1 is shown, and the connection relationship is as follows:

[0094] A first end of the voltage-dividing resistor unit is connected to the drain of the first MOS transistor M0, and a second end of the voltage-dividing resistor unit is grounded;

[0095] The third terminal of the voltage dividing resistor unit is connected to the first input terminal of the comparator OV Comp;

[0096] The second input terminal of the comparator OV Comp is used to receive the reference voltage VREF;

[0097] The output end of the comparator OV Comp is connected to the control end of the switch module Q1;

[0098] The switch module Q1 is connected in series with the current source I1.

[0099] Fig.12 In the embodiment, the negative feedback loop includes the operational amplifier EA, and the output end of the comparator OV Comp can also be connected to the power supply end of the operational amplifier EA. When the comparator OV Comp detects that the output voltage is too high, the output signal disconnects the switch module Q1 and the output signal can also stop the operational amplifier EA from working, thereby better ensuring that the output voltage is not too high and saving the power consumption of the operational amplifier EA.

[0100] like Fig.12 The comparison module may further include an offset voltage adjustment unit, the second input terminal of the comparator OV Comp is connected to the first terminal of the offset voltage adjustment unit, and the second terminal of the offset voltage adjustment unit is used to receive the first reference voltage. The offset voltage adjustment unit can make the working accuracy of the comparator OV Comp more accurate, and the specific principle is as follows:

[0101] The voltage across the offset voltage adjustment unit is recorded as Vos. When the feedback voltage FB exceeds VREF+Vos, overvoltage is determined. If the input voltage VIN has multiple continuous disturbances and the output voltage VOUT is extremely lightly loaded, the gate shutdown circuit alone cannot prevent the output voltage VOUT from floating up. The overvoltage discharge circuit can effectively clamp the output voltage VOUT to keep it at a lower value. The maximum value of the output voltage VOUT is:

[0102]

[0103] Vset in the formula is the set value of VOUT, which is obtained by dividing the feedback resistor voltage.

[0104] Fig.13 The gate cut-off circuit includes a switch tube and an AC voltage generating module. Each end of the AC voltage generating module has the following functions and connection relationships:

[0105] The first end of the AC voltage generating module is used to receive an input voltage VIN;

[0106] The second end of the AC voltage generating module is connected to the control end of the switch tube;

[0107] The third terminal of the AC voltage generating module is grounded;

[0108] The first end of the switch tube and the second end of the switch tube are connected between the gate and the source of the first MOS tube M0.

[0109] When the input voltage has an AC disturbance, the voltage generated by the AC voltage generating module turns on the switch tube, thereby reducing the gate-source voltage of the first MOS tube M0 and turning off the first MOS tube M0 to avoid excessive output voltage.

[0110] Fig.14 The embodiment of the AC voltage generating module including the third resistor unit R1, the fourth resistor unit R2 and the capacitor C1 is shown, and the connection relationship is as follows:

[0111] The first end of the third resistor unit R1 is used to receive the input voltage VIN;

[0112] The second end of the third resistance unit R1 is connected to the first end of the fourth resistance unit R2;

[0113] The second end of the fourth resistor unit R2 is connected to the first end of the capacitor C1;

[0114] The second terminal of the capacitor C1 is grounded.

[0115] The third resistor unit R1, the fourth resistor unit R2 and the capacitor C2 form a high-pass filter. When the input voltage VIN has an AC component, an additional voltage drop is generated across the third resistor unit R1. This voltage drop is also the gate-source voltage VGS1 of the switch tube M1:

[0116]

[0117] If the amplitude of the AC component of VIN is high enough and the frequency f is large enough to make VGS1 exceed the threshold VTH1 of the switch tube M1, the switch tube M1 is turned on to pull the gate-source voltage VGS of the first MOS tube M0 down to 0.

[0118] The high-pass filter mentioned above can be replaced by an active filter or the like which can realize the function of detecting the AC component.

[0119] Furthermore, when the first MOS tube M0 is turned off, if the output voltage VOUT across the output capacitor is still too high, the overvoltage discharge circuit can discharge the charge of the output capacitor in time.

[0120] In general, the present application proposes a linear regulator circuit, which can be used as a power stage of a linear regulator to solve the problem of output overvoltage caused by input voltage disturbance and achieve DC regulated output.

[0121] The above-described device and system embodiments are merely illustrative, and some or all of the modules may be selected according to actual needs to achieve the purpose of the present embodiment. A person skilled in the art may understand and implement the present embodiment without creative effort.

[0122] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A linear regulator circuit, characterized in that: It includes a first MOS tube, a negative feedback loop, a gate shutoff circuit and an overvoltage discharge circuit; The source of the first MOS tube is used to receive a first voltage, the drain of the first MOS tube is used to output a second voltage, the drain of the first MOS tube is connected to the first end of the overvoltage discharge circuit and the first end of the negative feedback loop; the second end of the negative feedback loop is connected to the gate of the first MOS tube; The second end of the overvoltage discharge circuit is grounded; The gate shutoff circuit is connected between the gate and the source of the first MOS tube; the gate shutoff circuit is used to generate a third voltage when the AC component of the first voltage is greater than a first set value, and the third voltage shuts off the first MOS tube; The overvoltage discharge circuit is used to release a part of the charge of the drain of the first MOS tube to the ground when the second voltage reaches a second set value.

2. The linear regulator circuit according to claim 1, characterized in that: The overvoltage discharge circuit includes a comparison module, a switch module and a ground current limiting module; The comparison module is used for outputting a signal to turn on the switch module when the second voltage reaches a second set value; When the switch module is turned on, a portion of the charge at the drain of the first MOS tube passes through the ground current limiting module to the ground.

3. The linear regulator circuit according to claim 2, characterized in that: The linear voltage regulator circuit further includes a voltage-dividing resistor unit; the drain of the first MOS tube is connected to the first end of the overvoltage discharge circuit through the voltage-dividing resistor unit; The comparison module includes a comparator; The first end of the voltage-dividing resistor unit is connected to the drain of the first MOS tube, the second end of the voltage-dividing resistor unit is grounded, and the third end of the voltage-dividing resistor unit is connected to the first input end of the comparator; The second input terminal of the comparator is used to receive a first reference voltage; The output end of the comparator is connected to the control end of the switch module.

4. The linear regulator circuit according to claim 3, characterized in that: The comparison module further includes an offset voltage adjustment unit, the second input terminal of the comparator is connected to the first terminal of the offset voltage adjustment unit, and the second terminal of the offset voltage adjustment unit is used to receive the first reference voltage.

5. The linear regulator circuit according to claim 3, characterized in that: The voltage-dividing resistor unit includes a first resistor unit and a second resistor unit; The first end of the first resistor unit is connected to the drain of the first MOS tube; The second end of the first resistance unit is connected to the second end of the second resistance unit and the first input end of the comparator; A second terminal of the second resistance unit is grounded.

6. The linear regulator circuit according to claim 2, characterized in that: The ground current limiting module includes a current source or a resistance module.

7. The linear regulator circuit according to claim 1, wherein: The gate shutoff circuit includes a switch tube and an AC voltage generating module; The first end of the AC voltage generating module is used to receive the first voltage; The second end of the AC voltage generating module is connected to the control end of the switch tube; The third terminal of the AC voltage generating module is grounded; The first end of the switch tube and the second end of the switch tube are connected between the gate and the source of the first MOS tube; the first MOS tube is an enhancement type PMOS tube.

8. The linear regulator circuit according to claim 7, characterized in that: The AC voltage generating module includes a third resistance unit, a fourth resistance unit and a capacitor; The first end of the third resistor unit is used to receive the first voltage; The second end of the third resistor unit is connected to the first end of the fourth resistor unit; The second end of the fourth resistor unit is connected to the first end of the capacitor; The second terminal of the capacitor is grounded.

9. The linear regulator circuit according to claim 1, wherein: The linear voltage regulator circuit further includes a voltage-dividing resistor unit; the drain of the first MOS tube is connected to the first end of the overvoltage discharge circuit and the first end of the negative feedback loop through the voltage-dividing resistor unit; The negative feedback loop includes an operational amplifier; the voltage-dividing resistor unit includes a first resistor unit and a second resistor unit; The first end of the first resistor unit is connected to the drain of the first MOS tube; The second end of the first resistance unit is connected to the second end of the second resistance unit and the first input end of the operational amplifier; The second end of the second resistance unit is grounded; The second input terminal of the operational amplifier is used to receive a second reference voltage; The output end of the operational amplifier is connected to the gate of the first MOS tube.

10. The linear regulator circuit according to claim 9, characterized in that: The overvoltage discharge circuit includes a comparison module, a switch module and a ground current limiting module; The comparison module is used for outputting a signal to turn on the switch module when the second voltage reaches a second set value; When the switch module is turned on, a portion of the charge of the drain of the first MOS tube passes through the ground current limiting module to the ground; The output end of the comparison module is connected to the power supply end of the operational amplifier.

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