CN215599330U

CN215599330U - Power failure detection system

Info

Publication number: CN215599330U
Application number: CN202120615328.XU
Authority: CN
Inventors: 陈强; 王冰; 沈剑; 黄嘉曦
Original assignee: Shenzhen Immotor Technology Co ltd
Current assignee: Shenzhen Immotor Technology Co ltd
Priority date: 2021-03-25
Filing date: 2021-03-25
Publication date: 2022-01-21
Anticipated expiration: 2031-03-25

Abstract

The utility model discloses a power failure detection system belongs to circuit detection technical field. The method comprises the following steps: the ESD protection circuit, the power failure detection circuit, the backflow prevention circuit and the MCU, wherein the power failure detection circuit comprises a voltage regulator tube, m first resistors and an MOS tube; the first end of the ESD protection circuit is connected with the anode of the external power supply, and the second end of the ESD protection circuit is connected with the cathode of the external power supply; the negative electrode of the voltage-regulator tube is connected with the first end of the ESD protection circuit, and the positive electrode of the voltage-regulator tube is connected with the first end of each first resistor; the grid electrode of the MOS tube is connected with the anode of the voltage regulator tube, the drain electrode of the MOS tube is connected with the second end of each first resistor and the second end of the ESD protection circuit, and the source electrode of the MOS tube is connected with the detection end of the MCU; the first end of the backflow prevention circuit is connected with the negative electrode of the voltage regulator tube, and the second end of the backflow prevention circuit is connected with the load and the standby power supply. MCU can accurately judge the power failure condition of external power supply in this application.

Description

Power failure detection system

Technical Field

The application relates to the technical field of circuit detection, in particular to a power failure detection system.

Background

With the development of technology, various electronic devices have entered into thousands of households. Some more important electronic devices need to be powered continuously, and therefore, the electronic devices need to be accurately detected in a real-time manner for power failure, so that the electronic devices can be powered by using a standby power supply in time.

In the related art, a base of the triode is connected to an external power supply through a resistor, and is connected to a standby power supply and a load through a backflow prevention device, an emitter of the triode is grounded through a resistor, and a collector of the triode is connected to an MCU (micro controller Unit). Normally, an external power source is used to power the load. If the external power supply is powered down, the voltage difference between the base electrode and the emitter electrode of the triode can be changed, so that the triode is turned off. The MCU determines that an external power supply is powered off after the triode is determined to be turned off by detecting the level output by the collector of the triode, and then starts a standby power supply to supply power to the load.

However, under the condition that the external power supply is powered off and the standby power supply is used for supplying power, the current output by the standby power supply flows through the backflow prevention device, the backflow prevention device has reverse leakage current, the reverse leakage current can cause the voltage difference between the base electrode and the emitter electrode of the triode to change, so that the triode is conducted, under the condition, the collector electrode of the triode can output the same level as that of the external power supply during normal working, the MCU is caused to mistakenly determine that the external power supply is not powered off, the MCU can mistakenly close the standby power supply at the moment, and the electronic equipment is not available.

SUMMERY OF THE UTILITY MODEL

The application provides a power failure detection system, can reach under the condition that uses stand-by power supply to supply power to the load, MCU can accurately judge the effect of the condition of falling the power of external power source. The technical scheme is as follows:

in a first aspect, a power failure detection system is provided, which includes: the ESD (Electro-Static Discharge) protection circuit comprises an ESD (Electro-Static Discharge) protection circuit, a power-down detection circuit, a backflow prevention circuit and an MCU (microprogrammed control unit), wherein the power-down detection circuit comprises a voltage-regulator tube, m first resistors and an MOS (Metal-Oxide-Semiconductor) tube, and m is a positive integer;

the first end of the ESD protection circuit is connected with the positive pole of an external power supply, and the second end of the ESD protection circuit is connected with the negative pole of the external power supply;

the negative electrode of the voltage-regulator tube is connected with the first end of the ESD protection circuit, and the positive electrode of the voltage-regulator tube is connected with the first end of each first resistor in the m first resistors; the grid electrode of the MOS tube is connected with the anode of the voltage stabilizing tube, the drain electrode of the MOS tube is connected with the second end of each first resistor in the m first resistors, the drain electrode of the MOS tube is connected with the second end of the ESD protection circuit, and the source electrode of the MOS tube is connected with the detection end of the MCU;

the first end of the backflow prevention circuit is connected with the negative electrode of the voltage regulator tube, the second end of the backflow prevention circuit is connected with the load and connected with the standby power supply, and the backflow prevention circuit is used for preventing the current of the standby power supply from flowing backwards.

In this application, under the condition that external power supply falls electric, external power supply does not export current, just there is not voltage on m first resistance so, just there is not voltage on the grid of MOS pipe this moment, therefore the MOS pipe is shut off, and the source electrode of MOS pipe can export corresponding level to MCU's detection end this moment, and MCU can confirm according to this that external power supply falls electric, and MCU can start stand-by power supply to control stand-by power supply. The current of the standby power supply flows into the load and simultaneously flows into the backflow preventing circuit. A great part of current in the current of the standby power supply is blocked by the backflow prevention circuit, however, a small part of current flows to the voltage stabilizing tube through the backflow prevention circuit, and the small part of current cannot breakdown the voltage stabilizing tube reversely. And because the voltage-regulator tube has one-way conductivity, and the reverse leakage current of the voltage-regulator tube is very small, only about 0.1 milliampere, so the current flowing from the voltage-regulator tube to each first resistor in the m first resistors and to the grid electrode of the MOS tube is very small under the condition, so the voltage generated on the grid electrode of the MOS tube is very small, the MOS tube is not enough to be conducted, and the MOS tube is still in a turn-off state. At the moment, the MCU still accurately determines that the external power supply is powered off, and the standby power supply cannot be turned off. Therefore, the effect that the MCU can accurately judge the power failure condition of the external power supply under the condition that the standby power supply is used for supplying power to the load can be achieved, the MCU can be effectively prevented from being mistakenly turned off to the standby power supply, and the usability of the electronic equipment is ensured.

Optionally, the ESD protection circuit comprises a second resistor;

the first end of the second resistor is connected with the anode of the external power supply, and the second end of the second resistor is connected with the cathode of the external power supply.

Optionally, the backflow prevention circuit includes n first diodes, where n is a positive integer;

and the anode of each first diode in the n first diodes is connected with the cathode of the voltage-stabilizing tube, and the cathode of each first diode in the n first diodes is connected with the load and the standby power supply.

Optionally, the power failure detection system further includes a filter circuit;

the first end of the filter circuit is connected with the first end of the ESD protection circuit, and the second end of the filter circuit is connected with the second end of the ESD protection circuit.

Optionally, the filter circuit includes k first capacitors, where k is a positive integer;

the first electrode plate of each of the k first capacitors is connected with the first end of the ESD protection circuit, and the second electrode plate of each of the k first capacitors is connected with the second end of the ESD protection circuit.

Optionally, the power failure detection system further includes an indication circuit, a first end of the indication circuit is connected to the first end of the ESD protection circuit, a second end of the indication circuit is connected to the second end of the ESD protection circuit, and the indication circuit is configured to indicate a working state of the external power supply.

Optionally, the indication circuit comprises a third resistor and a light emitting diode;

the first end of the third resistor is connected with the first end of the ESD protection circuit, the second end of the third resistor is connected with the anode of the light-emitting diode, and the cathode of the light-emitting diode is connected with the second end of the ESD protection circuit.

Optionally, the second terminal of the ESD protection circuit is connected to ground.

Optionally, the drain of the MOS transistor is connected to ground.

Optionally, a control end of the MCU is connected to the standby power supply for controlling the standby power supply.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

Fig. 1 is a circuit structure diagram of a first power down detection system according to an embodiment of the present application;

fig. 2 is a circuit structure diagram of a second power failure detection system according to an embodiment of the present application;

fig. 3 is a circuit structure diagram of a third power down detection system according to an embodiment of the present application;

fig. 4 is a circuit structure diagram of a fourth power failure detection system according to an embodiment of the present application;

fig. 5 is a circuit structure diagram of a fifth power failure detection system according to an embodiment of the present application;

fig. 6 is a circuit structure diagram of a sixth power failure detection system according to an embodiment of the present application;

fig. 7 is a circuit structure diagram of a seventh power down detection system according to an embodiment of the present application.

Reference numerals:

101: ESD protection circuit, 102: power down detection circuit, 103: backflow prevention circuit, 104: MCU, 105: external power supply, 106: load, 107: backup power supply, 108: filter circuit, 109: indication circuit, 110: backup power prevents flowing backward circuit, 111: a standby power supply filter circuit;

DZ: stabilivolt, R1: first resistance, R2: second resistance, R3: third resistance, Q: MOS tube, g: grid electrode of MOS tube, d: drain electrode of MOS tube, s: source of MOS transistor, D1: first diode, D2: second diode, C1: first capacitance, C2: second capacitance, L: a light emitting diode.

Detailed Description

To make the objects, technical solutions and advantages of the present application more clear, embodiments of the present application will be described in further detail below with reference to the accompanying drawings.

It should be understood that reference to "a plurality" in this application means two or more. In addition, for the convenience of clearly describing the technical solutions of the present application, the terms "first", "second", and the like are used to distinguish the same items or similar items having substantially the same functions and actions. Those skilled in the art will appreciate that the terms "first," "second," etc. do not denote any order or quantity, nor do the terms "first," "second," etc. denote any order or importance.

Before explaining the embodiments of the present application in detail, an application scenario of the embodiments of the present application will be described.

In daily production or life, some important electronic devices need uninterrupted power supply during working, but in actual working of the electronic devices, the external power supply may be powered off due to various uncertain factors, and some unnecessary losses may be caused once the external power supply is powered off. Therefore, the important electronic devices need to be accurately detected in real time to acquire the working condition of the external power supply in real time, and once the external power supply is found to be powered down, the important electronic devices can be timely powered by using the standby power supply, so that the requirement of uninterrupted power supply of the electronic devices is met.

Therefore, the power failure detection system provided by the embodiment of the application can achieve the effect that the MCU can accurately judge the power failure condition of the external power supply under the condition that the standby power supply is used for supplying power to a load, so that the MCU can be effectively prevented from being mistakenly turned off to the standby power supply, and the usability of the electronic equipment is ensured.

The power failure detection system provided by the embodiment of the application can be used for detecting power failure of a 6V direct-current external power supply, a 12V direct-current external power supply, a 24V direct-current external power supply, a 48V direct-current external power supply and direct-current external power supplies with other voltage levels, and the embodiment of the application is not limited to the power failure detection system.

The power failure detection system provided in the embodiment of the present application is explained in detail below.

Fig. 1 is a circuit structure diagram of a power failure detection system according to an embodiment of the present application. Referring to fig. 1, the power down detection system includes: the ESD protection circuit 101, the power failure detection circuit 102, the backflow prevention circuit 103 and the MCU104, wherein the power failure detection circuit 102 comprises a voltage regulator tube DZ, m first resistors R1 and an MOS tube Q, and m is a positive integer.

A first terminal of the ESD protection circuit 101 is connected to a positive terminal of the external power source 105, and a second terminal of the ESD protection circuit 101 is connected to a negative terminal of the external power source 105.

The negative electrode of the voltage regulator tube DZ is connected with the first end of the ESD protection circuit 101, and the positive electrode of the voltage regulator tube DZ is connected with the first end of each first resistor R1 in the m first resistors R1; the grid g of the MOS transistor Q is connected with the anode of the voltage regulator DZ, the drain d of the MOS transistor Q is connected with the second end of each first resistor R1 in the m first resistors R1, the drain d of the MOS transistor Q is connected with the second end of the ESD protection circuit 101, and the source s of the MOS transistor Q is connected with the detection end of the MCU 104.

The first end of the reverse flow prevention circuit 103 is connected with the negative electrode of the voltage regulator DZ, the second end of the reverse flow prevention circuit 103 is connected with the load 106 and the standby power supply 107, and the reverse flow prevention circuit 103 is used for preventing the current of the standby power supply 107 from flowing backwards.

The ESD protection circuit 101 is a circuit for preventing static electricity generated from the outside from affecting the inside of the circuit.

The voltage regulator DZ is a semiconductor device with high resistance until the critical reverse breakdown voltage, and has the characteristic of extremely small reverse leakage current. For example, in the case where the voltage level of the external power source 105 is 12V, the regulator DZ may be a model SZAF6.8A/1W regulator, and the regulator DZ has a regulated value VZ of 6.8V (volts), a regulated current IZ of 37mA (milliamperes), and a steady-state power consumption P of 1W (watts).

The backflow prevention circuit 103 is a circuit that prevents the current of the backup power supply 107 from flowing backward into the power down detection circuit 102 and the external power supply 105.

MCU104 is a chip-scale computer formed by appropriately reducing the frequency and specification of a cpu and integrating a memory, a counter, and various interfaces and circuits on a single chip.

The MOS transistor Q is a field effect transistor that can be used in an analog circuit and a digital circuit, can be used as an electronic switch, a controllable rectifier, and the like, and is a voltage-driven type device.

The load 106 may be various electronic devices, for example, the load 106 may be a camera, a fire sprinkler, an alarm, or the like, which is not limited in this embodiment.

In the power failure detection system provided in the embodiment of the present application, under the condition that the external power supply 105 works normally, the current output by the external power supply 105 sequentially flows to the load 106 through the ESD protection circuit 101, the power failure detection circuit 102, and the backflow prevention circuit 103, so as to supply power to the load 106. In this process, if static electricity exists, the ESD protection circuit 101 may conduct the static electricity away to protect other components in the power down detection system. The current flowing from the external power supply 105 to the voltage regulator DZ breaks down the voltage regulator DZ in the reverse direction, so that a large voltage is generated across the m first resistors R1, that is, a large voltage is generated across the gate g of the MOS transistor Q, and the MOS transistor Q is turned on, at this time, the source s of the MOS transistor Q outputs a corresponding level (for example, a low level) to the detection terminal of the MCU104, and the MCU104 can determine that the external power supply 105 operates normally according to the level, and does not start the standby power supply 107. In this case, power consumption by the zener diode DZ is relatively small.

However, under the condition that the external power source 105 is powered off, the external power source 105 does not output current, so that there is no voltage across the m first resistors R1, and there is no voltage across the gate g of the MOS transistor Q at this time, so that the MOS transistor Q is turned off, and at this time, the source s of the MOS transistor Q outputs a corresponding level (for example, a high level) to the detection end of the MCU104, so that the MCU104 can determine that the external power source 105 is powered off, and the MCU104 can start the standby power source 107 to control the standby power source 107 to supply power.

The current of the backup power supply 107 flows into the reverse flow prevention circuit 103 while flowing into the load 106. A large part of the current of the standby power supply 107 is blocked by the reverse flow prevention circuit 103, but a small part of the current flows to the voltage regulator DZ through the reverse flow prevention circuit 103, and the small part of the current cannot reversely break down the voltage regulator DZ. And because the voltage regulator tube DZ has one-way conductivity, and the reverse leakage current of the voltage regulator tube DZ is extremely small, only about 0.1 milliampere, under the condition, the current flowing from the voltage regulator tube DZ to each first resistor R1 in the m first resistors R1 and to the grid g of the MOS tube Q is very small, so the voltage generated on the grid g of the MOS tube Q is also very small, the MOS tube Q is not sufficiently conducted, and the MOS tube Q is still in a turn-off state. At this time, MCU104 still accurately determines that external power supply 105 is powered down and will not turn off standby power supply 107. Therefore, the effect that the power failure condition of the external power supply 105 can be accurately judged by the MCU104 under the condition that the standby power supply 107 is used for supplying power to the load 106 can be achieved, so that the error closing of the MCU104 on the standby power supply 107 can be effectively avoided, and the usability of the electronic equipment is ensured.

It is worth to be noted that the embodiment of the present application solves the problem of the MCU turning off the standby power supply by mistake, which may be generated by a common circuit in the related art, with a very low cost. The power failure detection system provided by the embodiment of the application is stable and reliable and is suitable for wide application.

Optionally, referring to fig. 2, the ESD protection circuit 101 includes a second resistor R2. A first terminal of the second resistor R2 is connected to the positive terminal of the external power source 105, and a second terminal of the second resistor R2 is connected to the negative terminal of the external power source 105.

The second resistor R2 may be a piezo-resistor. The voltage dependent resistor utilizes the voltage dependent characteristic of voltage dependent ceramic material, and when the voltage applied to two ends of the voltage dependent resistor is less than the voltage dependent voltage, the voltage dependent resistor is equivalent to an insulation resistor with the voltage of more than 10MQ (megaohms). When overvoltage larger than the voltage-sensitive voltage is applied to the two ends of the voltage-sensitive resistor, the resistance of the voltage-sensitive resistor is sharply reduced to present a low resistance state, so that charges are quickly conducted away. Therefore, the protection to static electricity can be realized, and other components in the circuit are effectively protected from being damaged due to overvoltage.

Optionally, referring to fig. 3, the anti-backflow circuit 103 includes n first diodes D1, where n is a positive integer. The anode of each of the n first diodes D1 and D1 is connected to the cathode of the zener diode DZ, and the cathode of each of the n first diodes D1 and D1 is connected to the load 106 and the backup power source 107.

The first diode D1 is an electronic element made of a semiconductor material, and the first diode D1 has unidirectional conductivity. That is, when a forward voltage is applied to the anode and cathode of the first diode D1, the first diode D1 is turned on. When a reverse voltage is applied to the positive electrode and the negative electrode of the first diode D1, the first diode D1 is turned off.

When the load 106 is supplied with power using the backup power supply 107, a current of the backup power supply 107 flows into the load 106 to supply the power. Meanwhile, the current of the standby power 107 flows into the cathode of the n first diodes D1, and the n first diodes D1 generate a reverse leakage current, which flows from the anode of the n first diodes D1 into the cathode of the regulator DZ.

It should be noted that, in the case of using the backup power source 107 to supply power to the load 106, the current outputted by the backup power source 107 flows into the cathodes of the n first diodes D1, and since the first diode D1 has the characteristic of unidirectional conduction, the current outputted by the backup power source 107 is blocked by the n first diodes D1. Therefore, the current of the standby power supply 107 can be effectively prevented from flowing backwards, the effects of protecting the external power supply 105, the ESD protection circuit 101 and the power failure detection circuit 102 can be achieved, and the normal power supply of the standby power supply 107 to the load 106 can be ensured.

Further, referring to fig. 4, the power down detection system further includes a filter circuit 108. A first terminal of the filter circuit 108 is connected to a first terminal of the ESD protection circuit 101, and a second terminal of the filter circuit 108 is connected to a second terminal of the ESD protection circuit 101. The filter circuit 108 may function to stabilize the voltage of the external power supply 105.

Under the condition that the external power supply 105 normally works, the current of the external power supply 105 flows through the ESD protection circuit 101 to eliminate static electricity and then flows into the filter circuit 108, the filter circuit 108 can stabilize the voltage of the external power supply 105, and the current flowing through the filter circuit 108 flows through the power failure detection circuit 102 and the backflow prevention circuit 103 and then flows into the load 106 to supply power to the load.

Optionally, the filter circuit 108 may include k first capacitors C1, k being a positive integer. A first plate of each of the k first capacitors C1 and C1 is connected to a first terminal of the ESD protection circuit 101, and a second plate of each of the k first capacitors C1 and C1 is connected to a second terminal of the ESD protection circuit 101.

It should be noted that in the embodiment of the present application, the k first capacitors D1 are connected in parallel to the ESD protection circuit 101 to the external power source 105, so as to implement the filtering function. The k first capacitors C1 are used to stabilize the filtered output voltage to a stable dc voltage. The operation principle of the k first capacitors C1 is that when the voltage of the external power source 105 is higher than the voltage of the k first capacitors C1, the k first capacitors C1 are charged, and when the voltage of the external power source 105 is lower than the voltage of the k first capacitors C1, the k first capacitors C1 are discharged. During the charging and discharging of the k first capacitors C1, the output voltage can be substantially stabilized.

Further, referring to fig. 5, the power down detection system further includes an indication circuit 109. A first terminal of the indication circuit 109 is connected to a first terminal of the ESD protection circuit 101, a second terminal of the indication circuit 109 is connected to a second terminal of the ESD protection circuit 101, and the indication circuit 109 is used for indicating an operation state of the external power supply 105.

When the external power source 105 operates normally, the current of the external power source 105 flows through the ESD protection circuit 101 to remove static electricity, and then flows into the indication circuit 109, and at this time, the indication circuit 109 can indicate the operating state of the external power source 105.

Optionally, the indication circuit 109 comprises a third resistor R3 and a light emitting diode L. A first end of the third resistor R3 is connected to a first end of the ESD protection circuit 101, a second end of the third resistor R3 is connected to an anode of the light emitting diode L, and a cathode of the light emitting diode L is connected to a second end of the ESD protection circuit 101.

The third resistor R3 can perform voltage dividing and current limiting functions to protect the led L from breakdown.

It should be noted that, when the external power supply 105 operates normally, the current flowing from the external power supply 105 flows into the indication circuit 109, and the light emitting diode L emits light normally, which indicates that the external power supply 105 operates normally. In the event that the external power source 105 is powered down, no current flows from the external power source 105 to the indicating circuit 109, and the light emitting diode L does not emit light, indicating that the external power source 105 is powered down.

Alternatively, referring to fig. 6, the second terminal of the ESD protection circuit 101 is connected to the ground. And the drain electrode d of the MOS tube Q is connected with the ground wire. Therefore, each circuit in the power failure detection system can be ensured to work stably and reliably, and the effect of protecting the personal safety of related personnel can be achieved.

Optionally, a control terminal of the MCU104 is connected to the backup power 107 for controlling the backup power 107. The MCU104 may turn off the standby power 107 when it determines that the external power 105 is operating normally; upon determining that the external power source 105 is powered down, the backup power source 107 is enabled.

In one possible implementation manner, referring to fig. 7, the power failure detection system may further include a backup power filter circuit 111 and a backup power backflow prevention circuit 110.

A first terminal of the backup power filter circuit 111 is connected to the positive terminal of the backup power 107, and a second terminal of the backup power filter circuit 111 is connected to the negative terminal of the backup power 107. The first end of the backup power supply backflow prevention circuit 110 is connected with the first end of the backup power supply filter circuit 110, and the second end of the backup power supply backflow prevention circuit 110 is connected with the load 106. The backup power filter circuit 111 can stabilize the voltage of the backup power 107, and the backup power anti-backflow circuit 110 can prevent the current of the external power 105 from flowing backward.

In the case where the load 106 is supplied with power from the backup power supply 107, the current of the backup power supply 107 flows into the backup power supply filter circuit 111 to stabilize the voltage, and then flows into the load 106 to supply power thereto.

Optionally, the second terminal of the standby power filter circuit 111 is connected to ground. Therefore, each circuit in the power failure detection system can be ensured to work stably and reliably, and the effect of protecting the personal safety of related personnel can be achieved.

Optionally, the standby power filter circuit 111 includes p second capacitors C2, where p is a positive integer. The first plate of each second capacitor C2 of the p second capacitors C2 is connected to the positive pole of the backup power source 107, and the second plate of each second capacitor C2 of the k second capacitors C2 is connected to the negative pole of the backup power source 107.

In the embodiment of the present application, the p second capacitors C2 are connected to the standby power supply 107 to implement the filtering function. The p second capacitors C2 are used to stabilize the filtered output voltage to a stable dc voltage. The p second capacitors C2 operate on the principle that when the voltage of the backup power source 107 is higher than the voltage of the p second capacitors C2, the p second capacitors C2 are charged. When the voltage of the standby power 107 is lower than the voltage of the p second capacitors C2, the p second capacitors C2 discharge. In the process of charging and discharging the p second capacitors C2, the output voltage can be basically stabilized.

Optionally, the backup power supply backflow prevention circuit 110 includes q second diodes D2, q being a positive integer. An anode of each of the q second diodes D2, D2, is connected to the first terminal of the backup power filter circuit 110, and a cathode of each of the q second diodes D2, D2, is connected to the load 106.

When the external power supply 105 operates normally, a current output from the external power supply 105 flows into the load 106 to supply power thereto. Meanwhile, the current output from the external power source 105 flows into the cathodes of the q second diodes D2. Since the q second diodes D2 have a unidirectional conduction characteristic, the current of the external power source 105 can be blocked. In this way, the current of the external power supply 105 can be prevented from flowing backward into the backup power supply filter circuit 111 and the backup power supply 107, and the effect of protecting the backup power supply filter circuit 111 and the backup power supply 107 can be achieved.

In this embodiment of the application, under the condition that the external power source 105 is powered down, the external power source 105 does not output current, and then there is no voltage across the m first resistors R1, and there is no voltage across the gate g of the MOS transistor Q at this time, so the MOS transistor Q is turned off, at this time, the source s of the MOS transistor Q may output a corresponding level to the detection end of the MCU104, and the MCU104 may determine that the external power source 105 is powered down accordingly, and the MCU104 may start the backup power source 107 to control the backup power source 107 to supply power. The current of the backup power supply 107 flows into the reverse flow prevention circuit 103 while flowing into the load 106. A large part of the current of the standby power supply 107 is blocked by the reverse flow prevention circuit 103, but a small part of the current flows to the voltage regulator DZ through the reverse flow prevention circuit 103, and the small part of the current cannot reversely break down the voltage regulator DZ. And because the voltage regulator tube DZ has one-way conductivity, and the reverse leakage current of the voltage regulator tube DZ is extremely small, only about 0.1 milliampere, under the condition, the current flowing from the voltage regulator tube DZ to each first resistor R1 in the m first resistors R1 and to the grid g of the MOS tube Q is very small, so the voltage generated on the grid g of the MOS tube Q is also very small, the MOS tube Q is not sufficiently conducted, and the MOS tube Q is still in a turn-off state. At this time, MCU104 still accurately determines that external power supply 105 is powered down and will not turn off standby power supply 107. Therefore, the effect that the power failure condition of the external power supply 105 can be accurately judged by the MCU104 under the condition that the standby power supply 107 is used for supplying power to the load 106 can be achieved, so that the error closing of the MCU104 on the standby power supply 107 can be effectively avoided, and the usability of the electronic equipment is ensured.

The above-mentioned embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present application and are intended to be included within the scope of the present application.

Claims

1. A power down detection system, comprising: the ESD protection circuit comprises an electrostatic discharge ESD protection circuit, a power failure detection circuit, a backflow prevention circuit and a micro control unit MCU, wherein the power failure detection circuit comprises a voltage regulator tube, m first resistors and a metal oxide semiconductor MOS tube, and m is a positive integer;

2. The power loss detection system of claim 1, wherein said ESD protection circuit comprises a second resistor;

3. The power loss detection system of claim 1, wherein the back-flow prevention circuit comprises n first diodes, wherein n is a positive integer;

4. The power loss detection system of claim 1, further comprising a filter circuit;

5. The power loss detection system of claim 4, wherein said filter circuit comprises k first capacitors, said k being a positive integer;

6. The power failure detection system of claim 1, further comprising an indication circuit, a first terminal of the indication circuit being connected to a first terminal of the ESD protection circuit, a second terminal of the indication circuit being connected to a second terminal of the ESD protection circuit, the indication circuit being configured to indicate an operating state of the external power source.

7. The power loss detection system of claim 6, wherein said indication circuit comprises a third resistor and a light emitting diode;

8. The power loss detection system of claim 1, wherein the second terminal of the ESD protection circuit is connected to ground.

9. The power failure detection system of claim 1, wherein a drain of the MOS transistor is connected to ground.

10. The power failure detection system according to any of claims 1-9, wherein a control terminal of the MCU is connected to the backup power supply for controlling the backup power supply.