CN207398814U - Undervoltage overvoltage protection circuit and power supply system - Google Patents

Abstract

The utility model discloses an under-voltage and over-voltage protection circuit, which comprises a power-off switch, an over-voltage detection unit and an under-voltage detection unit; a power supply system comprises a power module, an under-voltage and over-voltage protection circuit and a working module. Through mutual cooperation among the undervoltage detection unit, the overvoltage detection unit and the power-off switch which are composed of a plurality of simple electronic components, the power supply circuit has undervoltage protection and overvoltage protection functions at the same time, and the safety performance of the power supply system is improved.

Description

Undervoltage and overvoltage protection circuit and power supply system

technical field

The utility model belongs to the technical field of protection circuits, in particular to an undervoltage and overvoltage protection circuit and a power supply system.

Background technique

As shown in FIG. 1 , it is a partial structural schematic diagram of an overvoltage protection circuit of a power supply circuit in the prior art. The traditional power supply circuit only has the overvoltage protection function but cannot realize the undervoltage protection function, and the traditional undervoltage protection uses components such as operational amplifiers and comparators to realize the protection circuit. The cost of the undervoltage protection circuit is high, the components are many, the volume is large, and the control is relatively complicated.

Utility model content

The purpose of the utility model is to provide an undervoltage and overvoltage protection circuit and a power supply system, realize that the power supply circuit has both undervoltage protection and overvoltage protection functions, and improve the safety performance of the power supply system.

In order to solve the above technical problems, an embodiment of the utility model provides an undervoltage and overvoltage protection circuit, including a power-off switch, an overvoltage detection unit, and an undervoltage detection unit; wherein, the power-off switch has a power input terminal, a switch control terminal and power output terminal; the overvoltage detection unit has an overvoltage detection terminal and an overvoltage control terminal; the undervoltage detection unit has an undervoltage detection terminal and an undervoltage control terminal;

The undervoltage detection terminal of the undervoltage detection unit is connected to the power input terminal of the power-off switch, and the undervoltage control terminal of the undervoltage detection unit is connected to the switch control terminal of the power-off switch; the overvoltage The overvoltage detection terminal of the detection unit is connected to the undervoltage detection terminal of the undervoltage detection unit, and the overvoltage control terminal of the overvoltage detection unit is connected to the switch control terminal of the power-off switch.

Further, the undervoltage detection unit includes: a first voltage dividing resistor, a second voltage dividing resistor and a first switch tube;

The first end of the first voltage dividing resistor is connected to the undervoltage detection end of the undervoltage detection unit, and the second end of the first voltage dividing resistor is connected to the first end of the second voltage dividing resistor; The first terminal of the second voltage dividing resistor is connected to the control terminal of the first switch tube, and the second terminal of the second voltage dividing resistor is grounded; the input terminal of the first switch tube is connected to the undervoltage The undervoltage control terminal of the detection unit is connected, the input terminal of the first switch tube is also connected with the undervoltage detection terminal of the undervoltage detection unit, and the output terminal of the first switch tube is grounded.

Preferably, the undervoltage detection unit further includes: a first current limiting resistor connected between the input terminal of the first switch tube and the undervoltage control terminal of the undervoltage detection unit, connected to the first The Zener diode between the second terminal of the voltage dividing resistor and the first terminal of the second voltage dividing resistor and the first terminal connected to the input terminal of the first switching tube and the undervoltage detection terminal of the undervoltage detection unit Two current-limiting resistors; wherein, the cathode of the Zener diode is connected to the second end of the first voltage dividing resistor, and the anode of the Zener diode is connected to the first end of the second voltage dividing resistor.

Preferably, the first switch tube is an NPN transistor;

The control terminal of the first switch transistor corresponds to the base of the NPN transistor, the input terminal of the first switch transistor corresponds to the collector of the NPN transistor, and the output terminal of the first switch transistor corresponds to It is the emitter of the NPN transistor.

Further, the overvoltage detection unit includes: a second switch tube;

The control terminal of the second switch tube is connected to the overvoltage detection terminal of the overvoltage detection unit, the input terminal of the second switch tube is connected to the overvoltage detection terminal of the overvoltage detection unit, and the second switch tube is connected to the overvoltage detection terminal of the overvoltage detection unit. The output terminal of the switch tube is connected with the overvoltage control terminal of the overvoltage detection unit.

Preferably, the overvoltage detection unit further includes: a third voltage dividing resistor and a fourth voltage dividing resistor;

The first terminal of the third voltage dividing resistor is connected to the overvoltage detection terminal of the overvoltage detection unit, and the second terminal of the third voltage dividing resistor is connected to the control terminal of the second switching tube; the The first terminal of the fourth voltage dividing resistor is connected to the control terminal of the second switch tube, and the second terminal of the fourth voltage dividing resistor is grounded.

Preferably, the second switch transistor is a PNP transistor;

The control terminal of the second switch tube corresponds to the base of the PNP transistor, the input terminal of the second switch tube corresponds to the collector of the PNP transistor, and the output terminal of the second switch tube corresponds to It is the emitter of the PNP transistor.

Preferably, the power-off switch is a P-channel MOS transistor;

The switch control end of the power-off switch corresponds to the gate of the P-channel MOS transistor, the power input end of the power-off switch corresponds to the source of the P-channel MOS transistor, and the power input terminal of the power-off switch corresponds to the source of the P-channel MOS transistor. The output end of the power supply corresponds to the drain of the P-channel MOS transistor.

The embodiment of the utility model also provides a power supply system, including: a power supply module, an undervoltage and overvoltage protection circuit, and a working module; wherein,

The power module has a power output end, and the working module has a power input end;

The power output end of the power module is connected to the power input end of the power-off switch; the power input end of the working module is connected to the power output end of the power-off switch.

Compared with the prior art, the beneficial effect of the undervoltage and overvoltage protection circuit and power supply system of the present utility model is that: the operation of the power-off switch is controlled by setting the undervoltage detection unit and the overvoltage detection unit; When the voltage of the power input terminal of the electric switch is lower than a certain limit value, the undervoltage detection unit controls the power-off switch to be disconnected, and the power output terminal of the power-off switch does not supply power to the rear end, thereby realizing the undervoltage protection function; when the power-off switch When the voltage at the input terminal of the power supply is higher than a certain limit value, the overvoltage detection unit controls the power-off switch to be turned off, and the power output terminal of the power-off switch does not supply power to the back end, thereby realizing the overvoltage protection function. Through the mutual cooperation between the under-voltage detection unit, over-voltage detection unit and power-off switch composed of several simple electronic components, the problem that the traditional power supply circuit only has the over-voltage protection function but cannot realize the under-voltage protection function is solved at low cost. Realize that the power supply circuit has undervoltage protection and overvoltage protection functions at the same time, and improves the safety performance of the power supply system.

Description of drawings

Fig. 1 is a partial structural schematic diagram of an overvoltage protection circuit of a power supply circuit in the prior art;

Fig. 2 is a structural schematic diagram of an embodiment of the undervoltage and overvoltage protection circuit provided by the utility model;

Fig. 3 is the circuit schematic diagram of the second embodiment of the undervoltage and overvoltage protection circuit provided by the utility model;

Fig. 4 is the circuit schematic diagram of the third embodiment of the undervoltage and overvoltage protection circuit provided by the utility model

Fig. 5 is a schematic structural diagram of the power supply system provided by the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. example. Based on the embodiments of the present utility model, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of protection of the present utility model.

Referring to FIG. 2 , it is a schematic structural diagram of an embodiment of the undervoltage and overvoltage protection circuit provided by the present invention. The undervoltage and overvoltage protection circuit includes: a power-off switch 30 , an overvoltage detection unit 20 and an undervoltage detection unit 10 ; Wherein, the power-off switch 30 has a power input terminal, a switch control terminal and a power output terminal; the overvoltage detection unit 20 has an overvoltage detection terminal and an overvoltage control terminal; the undervoltage detection unit 10 has an undervoltage detection terminal and undervoltage control terminal;

The undervoltage detection terminal of the undervoltage detection unit 10 is connected to the power input terminal of the power-off switch 30, and the undervoltage control terminal of the undervoltage detection unit 10 is connected to the switch control terminal of the power-off switch 30; The overvoltage detection terminal of the overvoltage detection unit 20 is connected to the undervoltage detection terminal of the undervoltage detection unit 10, and the overvoltage control terminal of the overvoltage detection unit 20 is connected to the switch control terminal of the power-off switch 30. end connection.

It should be noted that an undervoltage and overvoltage protection circuit provided by the utility model controls the operation of the power-off switch by setting an undervoltage detection unit and an overvoltage detection unit; specifically, when the voltage of the power input terminal of the power-off switch is low At a certain limit, the under-voltage detection unit controls the power-off switch to be disconnected, and the power output end of the power-off switch does not supply power to the rear end, thereby realizing the under-voltage protection function; when the voltage of the power input end of the power-off switch is higher than When a certain limit value is reached, the overvoltage detection unit controls the power-off switch to be turned off, and the power output terminal of the power-off switch does not supply power to the rear end, thereby realizing the overvoltage protection function. Through the mutual cooperation between the under-voltage detection unit, over-voltage detection unit and power-off switch composed of several simple electronic components, the problem that the traditional power supply circuit only has the over-voltage protection function but cannot realize the under-voltage protection function is solved at low cost. Realize that the power supply circuit has both undervoltage protection and overvoltage protection functions.

As shown in FIG. 3 , it is a schematic circuit diagram of the second embodiment of the undervoltage and overvoltage protection circuit provided by the present invention.

The undervoltage and overvoltage protection circuit provided in this embodiment further optimizes the structure of some functional circuits on the basis of the above embodiments, as follows:

The undervoltage detection unit 10 includes: a first voltage dividing resistor RD1, a second voltage dividing resistor RD2 and a first switch tube Q1;

The first terminal of the first voltage dividing resistor RD1 is connected to the undervoltage detection terminal of the undervoltage detection unit 10, and the second terminal of the first voltage dividing resistor RD1 is connected to the second terminal of the second voltage dividing resistor RD2. connected at one end; the first end of the second voltage dividing resistor RD2 is connected to the control terminal of the first switching tube Q1, and the second end of the second voltage dividing resistor RD2 is grounded; the first switching tube Q1 The input terminal of the undervoltage detection unit 10 is connected to the undervoltage control terminal, and the input terminal of the first switch tube Q1 is also connected to the undervoltage detection terminal of the undervoltage detection unit 10. The first switch tube The output of Q1 is grounded.

Preferably, the undervoltage detection unit 10 further includes: a first current limiting resistor R1 connected between the input terminal of the first switching transistor Q1 and the undervoltage control terminal of the undervoltage detection unit 10; A voltage stabilizing diode D1 between the second end of the first voltage dividing resistor RD1 and the first end of the second voltage dividing resistor RD2; wherein, the cathode of the voltage stabilizing diode D1 is connected to the first voltage dividing The second end of the resistor RD1 is connected, the anode of the Zener diode D1 is connected to the first end of the second voltage dividing resistor RD2; the input end of the first switching transistor Q1 is connected to the undervoltage detection unit The second current limiting resistor R2 between the undervoltage detection terminals of 10. The under-voltage detection unit 10 divides the voltage detected by the under-voltage detection terminal of the under-voltage detection unit 10 through the first voltage dividing resistor RD1, the second voltage dividing resistor RD2 and the Zener diode D1, so that when When the voltage detected by the under-voltage detection terminal is the under-voltage point, the voltage U _RD2 across the second voltage dividing resistor RD2 is just equal to the conduction threshold of the first switching transistor Q1 (generally 0.6V).

Preferably, the first switching transistor Q1 is an NPN transistor;

The control terminal of the first switching transistor Q1 corresponds to the base of the NPN transistor, the input terminal of the first switching transistor Q1 corresponds to the collector of the NPN transistor, and the first switching transistor Q1 The output end corresponds to the emitter of the NPN transistor.

Further, the overvoltage detection unit 20 includes: a second switch tube Q2;

The control terminal of the second switch tube Q2 is connected to the overvoltage detection terminal of the overvoltage detection unit 20 , the input terminal of the second switch tube Q2 is connected to the overvoltage detection terminal of the overvoltage detection unit 20 , The output terminal of the second switch tube Q2 is connected to the overvoltage control terminal of the overvoltage detection unit 20 .

Preferably, the overvoltage detection unit 20 further includes: a third voltage dividing resistor RD3 and a fourth voltage dividing resistor RD4;

The first terminal of the third voltage dividing resistor RD3 is connected to the overvoltage detection terminal of the overvoltage detection unit 20, the second terminal of the third voltage dividing resistor RD3 is connected to the control terminal of the second switching tube Q2 connection; the first terminal of the fourth voltage dividing resistor RD4 is connected to the control terminal of the second switching transistor Q2, and the second terminal of the fourth voltage dividing resistor RD4 is grounded. The overvoltage detection unit 20 divides the voltage detected by the overvoltage detection terminal of the overvoltage detection unit 20 through the third voltage dividing resistor RD3, so that when the voltage value detected by the overvoltage detection terminal is too high When the voltage is lower than the voltage point, the voltage U _RD3 at both ends of the third voltage dividing resistor RD3 is just equal to the conduction threshold of the second switching transistor Q2 (generally 0.6V).

Preferably, the second switching transistor Q2 is a PNP transistor;

The control terminal of the second switching transistor Q2 corresponds to the base of the PNP transistor, the input terminal of the second switching transistor Q2 corresponds to the collector of the PNP transistor, and the second switching transistor Q2 The output end corresponds to the emitter of the PNP transistor.

Preferably, the power-off switch 30 is a P-channel MOS transistor;

The switch control end of the power-off switch 30 corresponds to the gate of the P-channel MOS transistor, the power input end of the power-off switch 30 corresponds to the source of the P-channel MOS transistor, and the power-off switch 30 corresponds to the source of the P-channel MOS transistor. The power output end of the switch 30 corresponds to the drain of the P-channel MOS transistor.

Preferably, the undervoltage and overvoltage protection circuit further includes: a capacitor C1 and a power supply grounding capacitor E1;

The first end of the capacitor C1 is connected to the power output end of the power-off switch 30, the second end of the capacitor C1 is grounded; the first end of the power supply grounding capacitor E1 is connected to the power supply of the power-off switch 30 The output end is connected, and the second end of the power supply grounding capacitor E1 is grounded.

As shown in FIG. 4 , it is a schematic circuit diagram of the third embodiment of the undervoltage and overvoltage protection circuit provided by the present invention. The under-voltage and over-voltage protection circuit provided in this embodiment provides another connection mode between the under-voltage detection unit 10 and the power input end of the power-off switch on the basis of the above-mentioned embodiments, as follows:

The overvoltage detection terminal of the overvoltage detection unit 20 is connected to the power input terminal of the power-off switch 30, and the overvoltage control terminal of the overvoltage detection unit 20 is connected to the switch control terminal of the power-off switch 30; The undervoltage detection terminal of the undervoltage detection unit 10 is connected to the second end of the third voltage dividing resistor RD3 of the overvoltage detection unit 20, and the input voltage of the power supply input terminal of the power-off switch is passed through the overvoltage detection unit. The voltage divided by the third voltage dividing resistor RD3 of the unit 20 is then input to the undervoltage detection port of the undervoltage detection unit 10, and the undervoltage control terminal of the undervoltage detection unit is connected to the switch control terminal of the power-off switch ; wherein, since the fourth voltage dividing resistor RD4 in the overvoltage detection unit 20 is equivalent to the first voltage dividing resistor RD1, the Zener diode D1 and the second voltage dividing resistor RD2 in the undervoltage detection unit 10 ; By replacing the fourth voltage dividing resistor RD4 in the overvoltage detection unit 20, another connection mode between the undervoltage detection unit 10 and the power input end of the power-off switch can be obtained.

When the undervoltage and overvoltage protection circuit is working, when the voltage of the power input terminal of the power-off switch 30 decreases, the voltage detected by the undervoltage detection terminal of the undervoltage detection module 10 becomes smaller, and then flows through the The current of the second voltage dividing resistor RD2 in the undervoltage detection unit 10 decreases, and the voltage U _RD2 at both ends of the second voltage dividing resistor RD2 will also decrease accordingly; since the overvoltage voltage point is greater than the undervoltage voltage point, the In the overvoltage detection unit 20, when the voltage at the power input terminal of the power-off switch 30 drops below the undervoltage voltage point, the voltage U _RD3 at both ends of the third voltage dividing resistor RD3 of the overvoltage detection unit 20 is smaller than that of the second switch. The conduction threshold of the tube Q2, the second switching tube Q2 is cut off, so the overvoltage detection unit 20 does not participate in controlling the power-off switch 30;

When the voltage at the power input terminal of the power-off switch 30 drops below the undervoltage voltage point, the voltage U _RD2 at both ends of the second voltage dividing resistor RD2 of the undervoltage detection unit 10 is smaller than the conductance of the first switching transistor Q1 threshold, the first switching tube Q1 is turned off, and at this time, the level of the undervoltage control terminal of the undervoltage detection unit 10 is pulled up by the first resistor R1 and the resistor R2 in the undervoltage detection unit 10, so that the The input terminal of the first switch tube Q1 gives a high-level signal to the undervoltage control terminal of the undervoltage detection unit 10; after the switch control terminal of the power-off switch 30 receives the high-level signal, the power-off The switch 30 changes from on to off, so that the power output terminal of the power-off switch 30 does not supply power to the rear end, and through the mutual cooperation between the under-voltage detection unit 10, the over-voltage detection unit 20 and the power-off switch 30, the power supply is realized. The undervoltage protection function of the circuit.

When the undervoltage and overvoltage protection circuit works normally, that is, when the voltage at the power input terminal of the power-off switch 30 is greater than the undervoltage voltage point and less than the overvoltage voltage point, the third voltage dividing resistor RD3 of the overvoltage detection unit 20 The voltage U _RD3 at both ends is less than the conduction threshold of the second switch tube Q2, the second switch tube Q2 is cut off, the overvoltage detection unit 20 does not participate in controlling the power-off switch 30, and the undervoltage detection unit The voltage U _RD2 at both ends of the second voltage dividing resistor RD2 of 10 is greater than the conduction threshold of the first switching tube Q1, and the first switching tube Q1 is turned on. Since the output terminal of the first switching tube Q1 is grounded, the The high level of the input terminal of the first switching tube Q1 is pulled low, causing the undervoltage control terminal of the undervoltage detection unit to output a low level, so that the power-off switch 30 is turned on, and the power-off switch 30 The output terminal of the power supply normally supplies power to the back end.

When the undervoltage and overvoltage protection circuit is working, when the voltage of the power input terminal of the power-off switch 30 rises, the voltage detected by the overvoltage detection terminal of the overvoltage detection module 20 becomes larger, and the voltage flowing through the overvoltage detection terminal increases. The current of the third voltage dividing resistor RD3 in the overvoltage detection module 20 increases; The voltage U RD3 at both ends of the three-divider resistor _RD3 is greater than the conduction threshold of the second switch tube Q2, the second switch tube Q2 is turned on, and the overvoltage is applied through the input terminal of the second switch tube Q2 The high-level signal of the overvoltage control terminal of the detection unit 20; because the overvoltage voltage point is greater than the undervoltage voltage point, when the voltage of the power input terminal of the power-off switch 30 of the undervoltage detection unit 10 rises above the overvoltage voltage point , the voltage U _RD2 across the second voltage dividing resistor RD2 of the undervoltage detection unit 10 is greater than the conduction threshold of the first switch transistor Q1, the first switch transistor Q1 is turned on, and the undervoltage detection unit 10 Both the first current-limiting resistor R1 and the second current-limiting resistor R2 are pull-up resistors, so that the switch control terminal of the final power-off switch 30 receives a high-level signal, and the power-off switch 30 is driven by The switch is turned off, so that the power output terminal of the power-off switch 30 does not supply power to the rear end, and the overvoltage protection of the power circuit is realized through the mutual cooperation between the undervoltage detection unit 10, the overvoltage detection unit 20 and the power-off switch 30 Function.

As shown in Figure 5, the embodiment of the utility model also provides a power supply system, including: a power supply module 301, an undervoltage and overvoltage protection circuit 302, and a working module 303; wherein,

The power module 301 has a power output end; the working module 303 has a power input end;

The power output end of the power module 301 is connected to the power input end of the power-off switch 30 , and the power input end of the working module 303 is connected to the power output end of the power-off switch 30 .

To sum up, the beneficial effects of an undervoltage and overvoltage protection circuit and power supply system of the present invention are: the operation of the power-off switch is controlled by setting the undervoltage detection unit and the overvoltage detection unit; specifically, when the power-off switch When the voltage at the power input terminal of the power supply is lower than a certain limit value, the undervoltage detection unit controls the power-off switch to be disconnected, and the power output terminal of the power-off switch does not supply power to the rear end, thereby realizing the undervoltage protection function; when the power-off switch is turned off When the voltage at the input terminal of the power supply is higher than a certain limit value, the overvoltage detection unit controls the power-off switch to be turned off, and the power output terminal of the power-off switch does not supply power to the back end, thereby realizing the overvoltage protection function. Through the mutual cooperation between the under-voltage detection unit, over-voltage detection unit and power-off switch composed of several simple electronic components, the problem that the traditional power supply circuit only has the over-voltage protection function but cannot realize the under-voltage protection function is solved at low cost. Realize that the power supply circuit has undervoltage protection and overvoltage protection functions at the same time, and improves the safety performance of the power supply system.

The above is a preferred embodiment of the present utility model, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present utility model, some improvements and modifications can also be made, these improvements and modifications It is also regarded as the protection scope of the present utility model.

Claims (9)

1. An under-voltage and over-voltage protection circuit is characterized by comprising a power-off switch, an over-voltage detection unit and an under-voltage detection unit; wherein the power-off switch has a power input terminal, a switch control terminal and a power output terminal; the overvoltage detection unit is provided with an overvoltage detection end and an overvoltage control end; the undervoltage detection unit is provided with an undervoltage detection end and an undervoltage control end;

the under-voltage detection end of the under-voltage detection unit is connected with the power supply input end of the power-off switch, and the under-voltage control end of the under-voltage detection unit is connected with the switch control end of the power-off switch; the overvoltage detection end of the overvoltage detection unit is connected with the undervoltage detection end of the undervoltage detection unit, and the overvoltage control end of the overvoltage detection unit is connected with the switch control end of the power-off switch.

2. The undervoltage and overvoltage protection circuit of claim 1, wherein the undervoltage detection unit comprises: the first voltage-dividing resistor, the second voltage-dividing resistor and the first switch tube;

a first end of the first voltage-dividing resistor is connected with an under-voltage detection end of the under-voltage detection unit, and a second end of the first voltage-dividing resistor is connected with a first end of the second voltage-dividing resistor; the first end of the second voltage-dividing resistor is connected with the control end of the first switching tube, and the second end of the second voltage-dividing resistor is grounded; the input end of the first switch tube is connected with the under-voltage control end of the under-voltage detection unit, the input end of the first switch tube is also connected with the under-voltage detection end of the under-voltage detection unit, and the output end of the first switch tube is grounded.

3. The undervoltage and overvoltage protection circuit of claim 2, wherein the undervoltage detection unit further comprises: the undervoltage detection circuit comprises a first switch tube, a second switch tube, a first voltage division resistor, a voltage stabilizing diode and a second voltage division resistor, wherein the first voltage division resistor is connected between the input end of the first switch tube and the undervoltage control end of the undervoltage detection unit; the cathode of the voltage stabilizing diode is connected with the second end of the first voltage dividing resistor, and the anode of the voltage stabilizing diode is connected with the first end of the second voltage dividing resistor.

4. The undervoltage and overvoltage protection circuit according to claim 2, wherein the first switching transistor is an NPN transistor;

the control end of the first switch tube corresponds to the base electrode of the NPN type triode, the input end of the first switch tube corresponds to the collector electrode of the NPN type triode, and the output end of the first switch tube corresponds to the emitter electrode of the NPN type triode.

5. The undervoltage overvoltage protection circuit of claim 1, wherein the overvoltage detection unit comprises: a second switching tube;

the control end of the second switch tube is connected with the overvoltage detection end of the overvoltage detection unit, the input end of the second switch tube is connected with the overvoltage detection end of the overvoltage detection unit, and the output end of the second switch tube is connected with the overvoltage control end of the overvoltage detection unit.

6. The undervoltage overvoltage protection circuit of claim 5, wherein the overvoltage detection unit further comprises: a third voltage dividing resistor and a fourth voltage dividing resistor;

a first end of the third voltage-dividing resistor is connected with an overvoltage detection end of the overvoltage detection unit, and a second end of the third voltage-dividing resistor is connected with a control end of the second switching tube; the first end of the fourth voltage-dividing resistor is connected with the control end of the second switch tube, and the second end of the fourth voltage-dividing resistor is grounded.

7. The undervoltage and overvoltage protection circuit according to claim 5, wherein said second switching transistor is a PNP type triode;

the control end of the second switch tube corresponds to the base electrode of the PNP type triode, the input end of the second switch tube corresponds to the collector electrode of the PNP type triode, and the output end of the second switch tube corresponds to the emitting electrode of the PNP type triode.

8. The undervoltage overvoltage protection circuit according to claim 1, wherein said power-off switch is a P-channel MOS transistor;

the switch control end of the power-off switch corresponds to the grid electrode of the P-channel MOS tube, the power input end of the power-off switch corresponds to the source electrode of the P-channel MOS tube, and the power output end of the power-off switch corresponds to the drain electrode of the P-channel MOS tube.

9. A power supply system is characterized by comprising a power supply module, an under-voltage and over-voltage protection circuit and a working module;

the undervoltage overvoltage protection circuit is the undervoltage overvoltage protection circuit of any one of claims 1 to 8;

the power supply module is provided with a power supply output end, and the working module is provided with a power supply input end;

the power supply output end of the power supply module is connected with the power supply input end of the power-off switch; and the power input end of the working module is connected with the power output end of the power-off switch.