CN220961659U

CN220961659U - Power failure detection circuit, mainboard and electronic equipment

Info

Publication number: CN220961659U
Application number: CN202322879145.0U
Authority: CN
Inventors: 荆嘉诚
Original assignee: Suzhou Yuankong Electronic Technology Co ltd
Current assignee: Suzhou Yuankong Electronic Technology Co ltd
Priority date: 2023-10-26
Filing date: 2023-10-26
Publication date: 2024-05-14
Anticipated expiration: 2033-10-26

Abstract

The embodiment of the application discloses a power failure detection circuit, a main board and electronic equipment, wherein the power failure detection circuit comprises a voltage division switching sub-circuit and a hysteresis comparison sub-circuit; the control signal input end of the voltage division switching sub-circuit is used for being connected with a power-off control pulse signal, the plurality of input ends of the voltage division switching sub-circuit are respectively used for being connected with corresponding input voltages, and the voltage division switching sub-circuit is used for outputting detection voltages through the detection output ends according to the power-off control pulse signal and the input voltages; the first input end of the hysteresis comparison sub-circuit is connected with the output end of the voltage division switching sub-circuit and is used for accessing the detection voltage; the second input end of the hysteresis comparison sub-circuit is used for accessing the reference voltage, and the third input end of the hysteresis comparison sub-circuit is accessed to a power supply; the output end of the hysteresis comparison sub-circuit is used for outputting a power failure detection result according to the comparison result of the detection voltage and the reference voltage. The scheme ensures that the hysteresis comparison sub-circuit can not be started due to voltage fluctuation at the power-on moment, and improves the accuracy of power-down detection.

Description

Power failure detection circuit, mainboard and electronic equipment

Technical Field

The embodiment of the application relates to the technical field of electronics, in particular to a power failure detection circuit, a main board and electronic equipment.

Background

Based on the industrial main board or the functional board of the Intel platform x86 architecture, it is necessary to design a power-down detection circuit, and data in industrial equipment are often important and sensitive, such as monitoring data in a production process, equipment states and the like. When the power-down condition occurs, the power-down detection circuit can timely find and trigger the correct operation so as to protect the integrity of data and prevent the data from losing. Most industrial equipment needs to operate continuously, and any power outage or fluctuation may lead to equipment failure or data corruption. The power failure detection circuit can timely monitor the power condition to trigger proper countermeasures to ensure the stability and reliability of the system.

The types of the power-down detection circuits in the related technology are various, and the inventor finds that the power-down detection circuits realized with low cost can not be started quickly under all power-down conditions and can not realize accurate detection under all power-down conditions when carrying out use analysis on the related various power-down detection circuits.

Disclosure of utility model

The utility model provides a power failure detection circuit, a main board and electronic equipment, which are used for solving the technical problems that the prior art can not be started quickly under all power failure conditions and can not realize accurate detection under various power failure conditions.

In a first aspect, an embodiment of the present application provides a power-down detection circuit, where the power-down detection circuit includes a voltage division switching sub-circuit and a hysteresis comparison sub-circuit;

The control signal input end of the voltage division switching sub-circuit is used for being connected with a power-off control pulse signal, the plurality of input ends of the voltage division switching sub-circuit are respectively used for being connected with corresponding input voltages, and the voltage division switching sub-circuit is used for outputting detection voltages through the detection output ends according to the power-off control pulse signal and the input voltages;

The first input end of the hysteresis comparison sub-circuit is connected with the output end of the voltage division switching sub-circuit and is used for accessing the detection voltage; the second input end of the hysteresis comparison sub-circuit is used for accessing the reference voltage, and the third input end of the hysteresis comparison sub-circuit is accessed to a power supply; the output end of the hysteresis comparison sub-circuit is used for outputting a power failure detection result according to the comparison result of the detection voltage and the reference voltage.

In a second aspect, an embodiment of the present application provides a motherboard, where the motherboard includes a microprocessor and the power-down detection circuit of the first aspect, a state detection end of the microprocessor is electrically connected to an output end of the hysteresis comparison sub-circuit, and a control output end of the microprocessor is electrically connected to a control signal input end of the voltage division switching sub-circuit.

In a third aspect, an embodiment of the present application provides an electronic device, including the motherboard of the second aspect.

The power failure detection circuit, the main board and the electronic equipment comprise a voltage division switching sub-circuit and a hysteresis comparison sub-circuit; the control signal input end of the voltage division switching sub-circuit is used for being connected with a power-off control pulse signal, the plurality of input ends of the voltage division switching sub-circuit are respectively used for being connected with corresponding input voltages, and the voltage division switching sub-circuit is used for outputting detection voltages through the detection output ends according to the power-off control pulse signal and the input voltages; the first input end of the hysteresis comparison sub-circuit is connected with the output end of the voltage division switching sub-circuit and is used for accessing the detection voltage; the second input end of the hysteresis comparison sub-circuit is used for accessing the reference voltage, and the third input end of the hysteresis comparison sub-circuit is accessed to a power supply; the output end of the hysteresis comparison sub-circuit is used for outputting a power failure detection result according to the comparison result of the detection voltage and the reference voltage. By adding the voltage division switching sub-circuit before the hysteresis comparison sub-circuit, the voltage division switching sub-circuit outputs controllable detection voltage corresponding to the current state to the hysteresis comparison sub-circuit according to the power-on state change and the power-off pulse control signal, so that the hysteresis comparison sub-circuit is prevented from being unable to be started due to voltage fluctuation at the power-on moment, and the accuracy of power-off detection is improved.

Drawings

Fig. 1 is a schematic circuit diagram of a power failure detection circuit according to an embodiment of the present application.

Fig. 2 is a schematic diagram of a relationship between an output voltage and an input voltage of a comparator in a power-down detection circuit according to an embodiment of the present application.

Fig. 3 is a waveform diagram of FLAG signal when 5VSB in the power-down detection circuit is powered down according to an embodiment of the present application.

Fig. 4 is a waveform diagram of a PMOS transistor gate in a power-down detection circuit according to an embodiment of the present application when power is on.

Detailed Description

The utility model is described in further detail below with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are for purposes of illustration and not of limitation. It should be further noted that, for convenience of description, only some, but not all of the structures related to the present utility model are shown in the drawings.

It should be noted that the present disclosure is not intended to be exhaustive of all of the alternative embodiments, and those skilled in the art will appreciate that any combination of the technical features may constitute alternative embodiments as long as the technical features are not mutually contradictory after reading the present disclosure.

The power failure detection circuits in the related art are various in types, and some power failure detection circuits which are applied to an industrial main board and are realized based on low cost are generally insensitive in monitoring power interruption, so that the power failure condition is delayed or not timely detected, and the risk of data loss or equipment failure exists. The reasons for these problems include that such power down detection circuits often require their own power supply to operate and work, and if the power supply is interrupted, the power down detection circuits themselves may not work properly, thereby losing their own detection function; and the reliability and stability of the power down detection circuit affects its ability to operate for long periods of time. For some power failure detection circuits, the design scheme may be naturally sensitive to environmental changes (such as temperature, humidity, etc.) or power fluctuations, and adverse effects on these factors may lead to misjudgment or damage. However, to achieve more accurate detection, a general technical idea is to specially design a complicated power-down detection circuit with high precision or special purpose according to the requirement of the use scene of the industrial main board, and the complicated circuit design and installation may increase the complexity of management and maintenance, so that the power-down detection circuit may require higher overall implementation cost, may not be acceptable in terms of economy for some application scenes, and cannot be popularized to all industrial main boards.

According to the technical problem, the voltage division switching sub-circuit is added before the hysteresis comparison sub-circuit, and the voltage division switching sub-circuit outputs the controllable detection voltage corresponding to the current state to the hysteresis comparison sub-circuit according to the power-on state change and the power-down pulse control signal, so that the hysteresis comparison sub-circuit is prevented from being unable to be started due to the voltage fluctuation at the power-on moment, and the accuracy of power-down detection is improved.

The following describes various embodiments of the present utility model in detail.

Please refer to fig. 1, which is a schematic circuit diagram of a power-down detection circuit according to an embodiment of the present application. As shown in fig. 1, the power failure detection circuit comprises a voltage division switching sub-circuit and a hysteresis comparison sub-circuit; the control signal input end of the voltage division switching sub-circuit is used for being connected with a power-off control pulse signal, the plurality of input ends of the voltage division switching sub-circuit are respectively used for being connected with corresponding input voltages, and the voltage division switching sub-circuit is used for outputting detection voltages through the detection output ends according to the power-off control pulse signal and the input voltages; the first input end of the hysteresis comparison sub-circuit is connected with the output end of the voltage division switching sub-circuit and is used for accessing the detection voltage; the second input end of the hysteresis comparison sub-circuit is used for accessing the reference voltage, and the third input end of the hysteresis comparison sub-circuit is accessed to a power supply; the output end of the hysteresis comparison sub-circuit is used for outputting a power failure detection result according to the comparison result of the detection voltage and the reference voltage.

In the embodiment of the application, the hysteresis comparison sub-circuit is a core circuit for realizing the function of detecting the lost part, and the voltage division switching sub-circuit is a key circuit for realizing accurate power failure detection at lower cost. When the power-down detection circuit in the embodiment of the application is used for power-down detection, the power-down detection is carried out by matching with a microprocessor in electronic equipment using the power-down detection circuit, all power supplies in the power-down detection circuit are designed according to ATX (Advanced Technology Extended, advanced technology extension) power supplies, and after an output end of a hysteresis comparison sub-circuit outputs an output signal corresponding to a power-down detection result to the microprocessor, the power supply of the comparator is then turned off. The whole power failure detection result is precisely controlled by the voltage division switching sub-circuit, the precise control of the threshold voltage of power failure of the comparator in the hysteresis comparison sub-circuit is realized, the low-cost design of the voltage division switching sub-circuit is easy to build and maintain, the influence of external environment is effectively reduced in the whole power failure detection process through low cost, the independent control of specific change states such as power-on and power-off is realized in a stable and reliable mode, the precise judgment of false triggering in normal use is realized based on the voltage division switching sub-circuit, and the effective response to abnormal conditions can be realized in some scenes needing long-time operation.

In a specific implementation manner, as shown in fig. 1, the voltage division switching subcircuit includes a first resistor R1, a second resistor R2, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a first capacitor C1, a triode Q1, a second NMOS transistor Q2, a third NMOS transistor Q3, and a fourth PMOS transistor Q4; the first end of the tenth resistor R10 is used as a control signal input end, and the second end of the tenth resistor R10 is electrically connected with the base electrode of the triode Q1; the collector of the triode Q1 is electrically connected with the first end of the ninth resistor R9 and the grid electrode of the second NMOS tube Q2; the drain electrode of the second NMOS tube Q2 is electrically connected with the first end of the eleventh resistor R11 and the grid electrode of the third NMOS tube Q3; the drain electrode of the third NMOS tube Q3 is electrically connected with the first end of the first resistor R1, the first end of the first capacitor C1 and the grid electrode of the fourth PMOS tube Q4; the source electrode of the fourth PMOS tube Q4 is electrically connected with the first end of the second resistor R2, and the drain electrode of the fourth PMOS tube Q4 is used as a detection output end; the second end of the ninth resistor R9 is used for accessing the input voltage of 3D3V_S5, the second end of the eleventh resistor R11 is used for accessing the input voltage of 3D3V_S5, the second end of the first resistor R1 is used for accessing the input voltage of 5V_S5, and the second end of the second resistor R2 is used for accessing the input voltage of 5 VSB; the emitter of the triode Q1, the source of the second NMOS tube Q2, the source of the third NMOS tube Q3 and the second end of the first capacitor C1 are all grounded.

For each electronic component in the voltage division switching sub-circuit, the resistance parameter of the first resistor R1 is 200Kohm, the resistance parameter of the second resistor R2 is 39Kohm, the resistance parameter of the ninth resistor R9 is 10Kohm, the resistance parameter of the tenth resistor R10 is 10Kohm, and the resistance parameter of the eleventh resistor R11 is 10Kohm. In addition, the capacitance parameter of the first capacitance C1 may be 1 μf. The triode Q1 may be a common NPN triode, for example, a triode with the model number LMBT3904L, the second NMOS tube Q2 and the third NMOS tube Q3 may be N-channel enhancement type MOSFETs, the fourth PMOS tube Q4 may be a P-channel enhancement type MOSFET, and the gate-source threshold voltage of the fourth PMOS tube Q4 may be-0.9V at most.

In another specific implementation, as shown in fig. 1, the hysteresis comparison sub-circuit includes a comparator U1, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, and a first diode D1; the first end of the third resistor R3, the first end of the fourth resistor R4 and the first end of the fifth resistor R5 are electrically connected with the detection output end of the voltage division switching subcircuit, the second end of the fifth resistor R5 is electrically connected with the normal phase input end of the comparator U1 and the first end of the seventh resistor R7, the reverse phase input end of the comparator U1 is electrically connected with the first end of the sixth resistor R6, the normal phase side power end of the comparator U1 is connected with a 5VSB input power supply, and the reverse phase side power supply end of the comparator U1 is grounded; the output end of the comparator U1, the second end of the seventh resistor R7 and the first end of the eighth resistor R8 are electrically connected with the cathode of the first diode D1, and the anode of the first diode D1 is used as the output end of the hysteresis comparison sub-circuit; the second end of the third resistor R3 is used for accessing the input voltage of 5 VSB; the second end of the fourth resistor R4 is grounded; the second end of the sixth resistor R6 is used for accessing a reference voltage; the second end of the eighth resistor is used for accessing the input voltage of 3D3V_S5.

For each component in the hysteresis comparison subcircuit, the model of the comparator U1 may be TLV7021. Other resistance parameters, for example, the third resistor R3 may be 100Kohm, the fourth resistor R4 may be 220Kohm, the fifth resistor R5, the sixth resistor R6 and the eighth resistor R8 may each be 10Kohm, and the seventh resistor R7 may be 1Mohm. Wherein the second end of the sixth resistor R6 is used for accessing a reference voltage of 3.3V. The comparator of TLV7021 is a single channel, micro-power comparator with low voltage operation and rail-to-rail input capability. The TLV7021 comparator adopts ultra-small size leadless packaging, has the size of 0.8mm multiplied by 0.8mm, is suitable for space-limited design, has excellent combination of speed and power consumption, has propagation delay of 260ns and has static power supply current of 5 mu A. This combination of fast response time and micro-power consumption enables the power supply system of the electronic device to monitor and respond quickly to fault conditions in time. The operating voltage ranges from 1.6V to 5.5V, compatible with 3V and 5V systems. The comparator also has the feature of no output phase inversion and internal hysteresis at the input overdrive. These characteristics make the present design suitable for accurate voltage monitoring in noisy and harsh environments and provide an open drain output stage.

When the power failure detection circuit realized based on the graph 1 is used for electronic equipment, the reference voltage is changed by utilizing the switch of the fourth PMOS tube Q4 so as to reach the threshold value for controlling power up and power down, the comparator U1 is adopted for accurately detecting the power failure, and the function of recovering the instantaneous fluctuation output of the input voltage in use is provided. The power-down detection circuit is used for detecting the voltage of 5VSB when the ATX power supply is abnormally powered down, and when the voltage of 5VSB falls to 4.75V, FLAG is changed from high to low, and the FLAG is output to a microprocessor of the electronic equipment for power-down control and protection.

If the power-down detection is performed by only the hysteresis comparing portion in the related art, for example, when the hysteresis comparing sub-circuit is formed by using the comparator U1 with the model of TLV7021 as a core in fig. 1, the relationship between the output voltage and the input voltage is shown in fig. 2, V _IN1 and V _IN1 respectively identify the rising threshold voltage and the falling threshold voltage, and the correspondence between V _IN1 and V _IN1 is confirmed by the following formula:

Where R5 represents the resistance value of the fifth resistor R5, R7 represents the resistance value of the seventh resistor R7, V _REF represents the reference voltage, and V _CC represents the input voltage. Based on the above formula, further analyzing fig. 1, the comparator U1 in the hysteresis comparison sub-circuit uses 5VSB as the input end and uses 3.3V as the reference voltage, so that V _IN1＝3.33V,V_IN2 = 3.25V can be calculated, the input 5V is divided by the third resistor R3 and the fourth resistor R4, when the voltage of the input end is reduced to 4.75V, the voltage of the input end is 3.26V, and when the voltage of the input end is continuously reduced to be less than V _IN2, the comparator U1 triggers the output to be pulled down. Because the V _IN1 clock is greater than V _IN2, the turn-on voltage output during power-on is always higher than the turn-off voltage output during power-off, and when the voltage regulator is used for power-off detection closer to the constant value of the input voltage, the problem that the comparator U1 cannot be started during power-on may be caused by voltage fluctuation.

After the voltage division switching subcircuit is designed in the embodiment of the present application, for example, after the voltage division switching subcircuit shown in fig. 1 is added, the source electrode of the fourth PMOS transistor Q4 is 5VSB, the first resistor R1 and the first capacitor C1 form a delay circuit, when the motherboard is powered on, the 5v_s5 will delay 150ms, the gate will delay to be turned on, at this time, V _GS is lower than the threshold voltage-0.9V, the fourth PMOS transistor Q4 is turned on, the second resistor R2 and the third resistor R3 are connected in parallel and form a voltage division with the fourth resistor R4, and when the voltage of the 5VSB is 3.75V, V _IN1 of 3.33V can be obtained at the input end, thereby avoiding the influence of the instantaneous voltage fluctuation of the power on. Fig. 3 and fig. 4 respectively show a waveform diagram of a FLAG signal when 5VSB in the power-down detection circuit is powered down and a waveform diagram of a gate of the fourth PMOS transistor Q4 when the gate is powered up.

After the 5V_S5 is stable, the voltage drop of the grid electrode and the source electrode of the fourth PMOS tube is equal, the fourth PMOS tube Q4 is closed, and the electronic equipment detects the voltage of 5VSB according to the originally designed threshold value. If the input voltage abnormally fluctuates during normal operation of the main board, the threshold voltage of V _IN2 is accidentally dropped, so that FLAG is changed from high to low, the system is not expected to be closed at the moment, and the comparator U1 needs to recover the detection state after fluctuation, for the scene, a CTRL control pin is reserved on a circuit, the microcontroller output of the system, a CTRL signal is very low after the normal operation of the system, when the microcontroller detects the system state at the moment after the voltage fluctuation, if the electricity of each phase is abnormal, the CTRL signal outputs a high pulse, the third NMOS tube Q3 is temporarily opened, the V _IN1 is reduced, and the comparator U1 recovers the detection state again. The pull-up power supply of the ninth resistor R9 can be changed according to the power supply required by the pin of the microprocessor, so that parameters can be autonomously defined according to different products to achieve the expected detection function. The circuit shown in fig. 1 shows a pull-up source of 3.3V. In line, the first diode D1 acts to eliminate 3.3V residual charge for FLAG. In terms of a specific circuit structure, the hysteresis comparison sub-circuit does not adopt BJT but adopts MOS tube, so that false triggering caused by temperature drift in high-temperature and low-temperature environments can be prevented. In whole, the cost is considered in the device of this design, and main device is simple comparator and resistance and MOS pipe, and the overall arrangement is simple, and maintenance cost has obvious advantage.

The embodiment of the application further provides a main board, which comprises a microprocessor and any one of the power failure detection circuits in the previous embodiment, wherein the state detection end of the microprocessor is electrically connected with the output end of the hysteresis comparison sub-circuit, and the control output end of the microprocessor is electrically connected with the control signal input end of the voltage division switching sub-circuit. The specific implementation of the improvement related to the embodiment of the present application is described in the corresponding embodiment of the power failure detection circuit, and will not be repeated here. In the whole, the mainboard using the power failure detection circuit correspondingly has the corresponding beneficial effects.

The embodiment of the application finally provides an electronic device, which comprises the main board in any of the previous embodiments. The specific implementation of the improvement related to the embodiment of the present application is described in the corresponding embodiments of the power failure detection circuit and the motherboard, and will not be repeated here. In the whole, the electronic equipment using the main board correspondingly has the corresponding beneficial effects.

It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises an element.

Note that the above is only a preferred embodiment of the present utility model and the technical principle applied. It will be understood by those skilled in the art that the present utility model is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the utility model. Therefore, while the utility model has been described in connection with the above embodiments, the utility model is not limited to the embodiments, but may be embodied in many other equivalent forms without departing from the spirit or scope of the utility model, which is set forth in the following claims.

Claims

1. The power failure detection circuit is characterized by comprising a voltage division switching sub-circuit and a hysteresis comparison sub-circuit;

The control signal input end of the voltage division switching sub-circuit is used for being connected with a power-off control pulse signal, the plurality of input ends of the voltage division switching sub-circuit are respectively used for being connected with corresponding input voltages, and the voltage division switching sub-circuit is used for outputting detection voltages through the detection output end according to the power-off control pulse signal and the input voltages;

The first input end of the hysteresis comparison sub-circuit is connected with the output end of the voltage division switching sub-circuit and is used for accessing the detection voltage; the second input end of the hysteresis comparison sub-circuit is used for being connected with a reference voltage, and the third input end of the hysteresis comparison sub-circuit is connected with a power supply; and the output end of the hysteresis comparison sub-circuit is used for outputting a power failure detection result according to the comparison result of the detection voltage and the reference voltage.

2. The power failure detection circuit according to claim 1, wherein the voltage division switching sub-circuit includes a first resistor R1, a second resistor R2, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a first capacitor C1, a triode Q1, a second NMOS transistor Q2, a third NMOS transistor Q3, and a fourth PMOS transistor Q4;

A first end of the tenth resistor R10 is used as a control signal input end, and a second end of the tenth resistor R10 is electrically connected with the base electrode of the triode Q1; the collector of the triode Q1 is electrically connected with the first end of the ninth resistor R9 and the grid electrode of the second NMOS tube Q2; the drain electrode of the second NMOS transistor Q2 is electrically connected to the first end of the eleventh resistor R11 and the gate electrode of the third NMOS transistor Q3; the drain electrode of the third NMOS transistor Q3 is electrically connected to the first end of the first resistor R1, the first end of the first capacitor C1, and the gate electrode of the fourth PMOS transistor Q4; the source electrode of the fourth PMOS tube Q4 is electrically connected with the first end of the second resistor R2, and the drain electrode of the fourth PMOS tube Q4 is used as the detection output end; the second end of the ninth resistor R9 is used for accessing the input voltage of 3d3v_s5, the second end of the eleventh resistor R11 is used for accessing the input voltage of 3d3v_s5, the second end of the first resistor R1 is used for accessing the input voltage of 5v_s5, and the second end of the second resistor R2 is used for accessing the input voltage of 5 VSB; the emitter of the triode Q1, the source of the second NMOS tube Q2, the source of the third NMOS tube Q3 and the second end of the first capacitor C1 are all grounded.

3. The power down detection circuit of claim 2, wherein the first resistor R1 has a resistance parameter of 200Kohm, the second resistor R2 has a resistance parameter of 39Kohm, the ninth resistor R9 has a resistance parameter of 10Kohm, the tenth resistor R10 has a resistance parameter of 10Kohm, and the eleventh resistor R11 has a resistance parameter of 10Kohm.

4. A power loss detection circuit according to claim 2 or 3, wherein the capacitance parameter of the first capacitance C1 is 1 μf.

5. A power down detection circuit according to any one of claims 1-3, wherein the hysteresis comparison sub-circuit comprises a comparator U1, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, and a first diode D1;

The first end of the third resistor R3, the first end of the fourth resistor R4 and the first end of the fifth resistor R5 are all electrically connected with the detection output end of the voltage division switching subcircuit, the second end of the fifth resistor R5 is electrically connected with the non-inverting input end of the comparator U1 and the first end of the seventh resistor R7, the inverting input end of the comparator U1 is electrically connected with the first end of the sixth resistor R6, the non-inverting side power supply end of the comparator U1 is connected with a 5VSB input power supply, and the inverting side power supply end of the comparator U1 is grounded; the output end of the comparator U1, the second end of the seventh resistor R7 and the first end of the eighth resistor R8 are electrically connected with the negative electrode of the first diode D1, and the positive electrode of the first diode D1 is used as the output end of the hysteresis comparison sub-circuit; the second end of the third resistor R3 is used for accessing an input voltage of 5 VSB; the second end of the fourth resistor R4 is grounded; the second end of the sixth resistor R6 is used for accessing a reference voltage; the second end of the eighth resistor is used for accessing the input voltage of 3D3V_S5.

6. The power down detection circuit of claim 5, wherein the comparator U1 is of a type TLV7021.

7. The power down detection circuit of claim 5, wherein the third resistor R3 has a resistance parameter of 100Kohm, the fourth resistor R4 has a resistance parameter of 220Kohm, the fifth resistor R5, the sixth resistor R6 and the eighth resistor R8 each have a resistance parameter of 10Kohm, and the seventh resistor R7 has a resistance parameter of 1Mohm.

8. The power down detection circuit of claim 5, wherein the second terminal of the sixth resistor R6 is configured to be connected to a reference voltage of 3.3V.

9. The main board is characterized by comprising a microprocessor and the power failure detection circuit as claimed in any one of claims 1-8, wherein a state detection end of the microprocessor is electrically connected with an output end of the hysteresis comparison sub-circuit, and a control output end of the microprocessor is electrically connected with a control signal input end of the voltage division switching sub-circuit.

10. An electronic device comprising the motherboard of claim 9.