阅读说明：本技术 一种断电重启自控电路 (Power-off restart automatic control circuit ) 是由 张虎 戴毅欣 肖立志 吴笑馨 彭亮明 代飞 王业流 殷源 罗永升 于 2020-06-30 设计创作，主要内容包括：本发明涉及电子电路控制领域,更具体的说,涉及一种断电重启自控电路。本发明提出的断电重启自控电路,用于控制硬件电路板的断电重启,包括硬件电路板,发送断电复位信号给充放电回路模块,控制充放电回路模块进行充放电；充放电回路模块,输出充电电压或放电电压作为比较电压到比较电路模块；比较电路模块,根据比较电压与参考电压进行比较,输出开关断开信号或开关导通信号到开关电路模块；开关电路模块,根据开关断开信号或开关导通信号,控制开关电路模块的电路断开或导通,控制电源模块是否为硬件电路板供电。本发明通过少量元器件,控制整个硬件电路板的完全断电重启,断电持续时间可调整,减少人为断电重启操作,减少电路板故障率。(The invention relates to the field of electronic circuit control, in particular to a power-off restarting automatic control circuit. The invention provides a power-off restart self-control circuit which is used for controlling the power-off restart of a hardware circuit board and comprises the hardware circuit board, a charge-discharge loop module and a power-off reset module, wherein the hardware circuit board sends a power-off reset signal to the charge-discharge loop module and controls the charge-discharge loop module to charge and discharge; the charging and discharging loop module outputs charging voltage or discharging voltage as comparison voltage to the comparison circuit module; the comparison circuit module is used for comparing the comparison voltage with the reference voltage and outputting a switch off signal or a switch on signal to the switch circuit module; and the switch circuit module controls the circuit of the switch circuit module to be switched off or switched on according to the switch off signal or the switch on signal, and controls whether the power supply module supplies power to the hardware circuit board. According to the invention, the complete power-off restarting of the whole hardware circuit board is controlled through a small number of components, the power-off duration time is adjustable, the manual power-off restarting operation is reduced, and the fault rate of the circuit board is reduced.)

1. The utility model provides a power failure restart automatic control circuit for the power failure restart of control hardware circuit board, its characterized in that includes comparison circuit module, charge-discharge circuit module, switch circuit module and power module:

the hardware circuit board is connected with the charge-discharge loop module, sends a power-off reset signal to the charge-discharge loop module and controls the charge-discharge loop module to charge and discharge;

the charging and discharging loop module is connected with the comparison circuit module and outputs charging voltage or discharging voltage serving as comparison voltage to the comparison circuit module;

the comparison circuit module is connected with the switch circuit module, compares the comparison voltage with the reference voltage and outputs a switch off signal or a switch on signal to the switch circuit module;

the switch circuit module is connected with the power supply module, and controls the circuit of the switch circuit module to be switched off or switched on according to the switch off signal or the switch on signal, and controls whether the power supply module supplies power for the hardware circuit board.

2. The power down restart auto-control circuit of claim 1, wherein:

the charging and discharging loop module is used for charging after receiving the power-off reset signal, and when the charging voltage is higher than the reference voltage of the comparison circuit module, the comparison circuit module outputs a switch off signal;

and the charging and discharging loop module discharges after the hardware circuit board is powered off, and when the discharging voltage is lower than the reference voltage of the comparison circuit module, the comparison circuit module outputs a switch conducting signal.

3. The power outage restart automatic control circuit of claim 1, wherein the charge and discharge loop module comprises a fourth resistor R4, a fifth resistor R5, a diode V1, a sixth resistor R6 and a first capacitor C1:

one end of the fourth resistor R4 is connected with a power-off reset signal end of the hardware circuit board, and the other end of the fourth resistor R4 is grounded;

one end of the fifth resistor R5 is connected with a power-off reset signal end of the hardware circuit board, and the other end of the fifth resistor R5 is connected with the anode of the diode V1;

the cathode of the diode V1 is connected with the comparison voltage input end of the comparison circuit module;

one end of the sixth resistor R6 is connected with the cathode of the diode V1, and the other end of the sixth resistor R6 is grounded;

one end of the first capacitor C1 is connected with the cathode of the diode V1, and the other end is grounded.

4. The power-off restarting automatic control circuit according to claim 3, wherein the power module comprises a front-end power supply end and power conversion unit:

the front-end power supply end supplies power to the whole circuit;

one end of the power supply conversion unit is connected with the switch circuit module, the other end of the power supply conversion unit is connected with the hardware circuit board, and the voltage input by the switch circuit module is converted into the voltage suitable for the hardware circuit board.

5. The power-down restart automatic control circuit of claim 4, wherein the comparison circuit module comprises a comparator N1A, a first resistor R1, a second resistor R2 and a third resistor R3:

one end of the first resistor R1 is connected with the front end power supply end, and the other end of the first resistor R1 is connected with the reference voltage input end of the comparator N1A;

one end of the second resistor R2 is connected with the reference voltage input end of the comparator N1A, and the other end of the second resistor R2 is grounded;

one end of the third resistor R3 is connected with the reference voltage input end of the comparator N1A, and the other end is connected with the output end of the comparator N1A.

6. The power-off restarting automatic control circuit according to claim 5, wherein the switch circuit module comprises a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a triode V2 and a field effect transistor V3:

one end of the seventh resistor R7 is connected with the front end power supply end, and the other end of the seventh resistor R7 is connected with the output end of the comparator N1A;

one end of the eighth resistor R8 is connected with the output end of the comparator N1A, and the other end of the eighth resistor R8 is connected with the base electrode of the triode V2;

the emitter of the triode V2 is grounded, and the collector of the triode V2 is connected with one end of a ninth resistor R9;

the other end of the ninth resistor R9 is connected with a front-end power supply end;

the source electrode of the field effect transistor V3 is connected with the front end power supply end, the grid electrode of the field effect transistor V3 is connected with the collector electrode of the triode V2, and the drain electrode of the field effect transistor V3 is connected with the power supply conversion unit.

7. The power-down restart automatic control circuit of claim 3, wherein the charging time of the charge-discharge loop module is proportional to the product of the fifth resistor R5 and the first capacitor C1.

8. The auto-control circuit for restarting after power failure of claim 5, wherein the discharging time of the charge and discharge loop module is proportional to the product of the sixth resistor R6, the first capacitor C1 and a reference voltage threshold Vh, and the reference voltage threshold Vh is the difference between the maximum value and the minimum value of the reference voltage.

9. The power-off restart automatic control circuit according to claim 8, wherein the reference voltage threshold Vh is calculated by the following formula:

Vh＝R1R2Vo/(R1R2+R1R3+R2R3

wherein Vo is the output voltage of the output terminal of the comparator N1A.

10. The power-off restarting automatic control circuit according to claim 6, wherein the output voltage Vo at the output end of the comparator N1A is calculated by the formula:

VCC _ IN is the voltage value of the front end power supply end, Vbe is the conduction voltage of the triode V2, and Vcmp1 is the maximum value of the reference voltage.

Technical Field

The invention relates to the field of electronic circuit control, in particular to a power-off restarting automatic control circuit.

Background

In some railway electronic product applications, because the electronic product runs without power failure for a long time, system work is easy to be abnormal, and software reset is invalid, while the existing hardware power failure reset can only aim at a small part of circuits, can not control the power failure of key parts such as a CPU (central processing unit), and especially can not control the power failure restart of the whole circuit board.

For example, a Beidou/GPS plug-in a locomotive vehicle-mounted comprehensive information monitoring device (LDP) requires 24-hour uninterrupted work, a hardware watchdog circuit is arranged in the plug-in, the working states of a power supply and a processor can be monitored in real time, partial power supply reset circuits are arranged, some fault conditions exist, the fault cannot be solved by partial circuit outage reset, and the fault can be eliminated by complete outage restart.

The chinese utility model patent CN201822127613.8 discloses a system crash self-recovery device, which comprises a power module, a power control module and a system control module; the power supply control module comprises a power supply control chip, a triode and a relay; the system control module is connected with the power control chip and outputs a synchronous signal with set frequency to the power control chip; the relay is connected with the power supply module and controls the power supply module to be switched on and switched off; the power control chip is connected with the relay through the triode, if the power control chip does not receive a synchronous signal within the first set time, the triode is controlled to be conducted, and then the relay is controlled to work, so that the power module is powered off, and the triode is controlled to be cut off within the second set time, so that the relay is controlled to stop working, the power module is enabled to supply power again, and therefore the automatic power-off restarting of the system is achieved. The patent can only restart when the computer is halted, and can not restart the computer in a completely power-off manner at any time in a controllable manner when the functions are abnormal.

Disclosure of Invention

The invention aims to provide a power-off restart automatic control circuit, which solves the technical problem that a hardware circuit board in the prior art is difficult to completely automatically power off, restart and reset.

In order to achieve the above object, the present invention provides an automatic power-off restart control circuit for controlling power-off restart of a hardware circuit board, comprising a comparison circuit module, a charge-discharge loop module, a switch circuit module and a power supply module:

the hardware circuit board is connected with the charge-discharge loop module, sends a power-off reset signal to the charge-discharge loop module and controls the charge-discharge loop module to charge and discharge;

the charging and discharging loop module is connected with the comparison circuit module and outputs charging voltage or discharging voltage serving as comparison voltage to the comparison circuit module;

the comparison circuit module is connected with the switch circuit module, compares the comparison voltage with the reference voltage and outputs a switch off signal or a switch on signal to the switch circuit module;

the switch circuit module is connected with the power supply module, and controls the circuit of the switch circuit module to be switched off or switched on according to the switch off signal or the switch on signal, and controls whether the power supply module supplies power for the hardware circuit board.

In one embodiment, the charging and discharging loop module performs charging after receiving the power-off reset signal, and when the charging voltage is higher than the reference voltage of the comparison circuit module, the comparison circuit module outputs a switch-off signal;

and the charging and discharging loop module discharges after the hardware circuit board is powered off, and when the discharging voltage is lower than the reference voltage of the comparison circuit module, the comparison circuit module outputs a switch conducting signal.

In an embodiment, the charge and discharge circuit module includes a fourth resistor R4, a fifth resistor R5, a diode V1, a sixth resistor R6, and a first capacitor C1:

one end of the fourth resistor R4 is connected with a power-off reset signal end of the hardware circuit board, and the other end of the fourth resistor R4 is grounded;

one end of the fifth resistor R5 is connected with a power-off reset signal end of the hardware circuit board, and the other end of the fifth resistor R5 is connected with the anode of the diode V1;

the cathode of the diode V1 is connected with the comparison voltage input end of the comparison circuit module;

one end of the sixth resistor R6 is connected with the cathode of the diode V1, and the other end of the sixth resistor R6 is grounded;

one end of the first capacitor C1 is connected with the cathode of the diode V1, and the other end is grounded.

In one embodiment, the power module includes a front-end power supply terminal and a power conversion unit:

the front-end power supply end supplies power to the whole circuit;

one end of the power supply conversion unit is connected with the switch circuit module, the other end of the power supply conversion unit is connected with the hardware circuit board, and the voltage input by the switch circuit module is converted into the voltage suitable for the hardware circuit board.

In one embodiment, the comparison circuit module includes a comparator N1A, a first resistor R1, a second resistor R2, and a third resistor R3:

one end of the first resistor R1 is connected with the front end power supply end, and the other end of the first resistor R1 is connected with the reference voltage input end of the comparator N1A;

one end of the second resistor R2 is connected with the reference voltage input end of the comparator N1A, and the other end of the second resistor R2 is grounded;

one end of the third resistor R3 is connected with the reference voltage input end of the comparator N1A, and the other end is connected with the output end of the comparator N1A.

In one embodiment, the switch circuit module includes a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a transistor V2, and a fet V3:

one end of the seventh resistor R7 is connected with the front end power supply end, and the other end of the seventh resistor R7 is connected with the output end of the comparator N1A;

one end of the eighth resistor R8 is connected with the output end of the comparator N1A, and the other end of the eighth resistor R8 is connected with the base electrode of the triode V2;

the emitter of the triode V2 is grounded, and the collector of the triode V2 is connected with one end of a ninth resistor R9;

the other end of the ninth resistor R9 is connected with a front-end power supply end;

the source electrode of the field effect transistor V3 is connected with the front end power supply end, the grid electrode of the field effect transistor V3 is connected with the collector electrode of the triode V2, and the drain electrode of the field effect transistor V3 is connected with the power supply conversion unit.

In one embodiment, the charging time of the charging and discharging loop module is proportional to the product of the fifth resistor R5 and the first capacitor C1.

In one embodiment, the discharge time of the charge and discharge loop module is proportional to a product of the sixth resistor R6, the first capacitor C1 and a reference voltage threshold Vh, where the reference voltage threshold Vh is a difference between a maximum value and a minimum value of the reference voltage.

In an embodiment, the reference voltage threshold Vh is calculated by the following formula:

Vh＝R1R2Vo/(R1R2+R1R3+R2R3)

wherein Vo is the output voltage of the output terminal of the comparator N1A.

In one embodiment, the output voltage Vo at the output terminal of the comparator N1A is calculated by the following formula:

VCC _ IN is the voltage value of the front end power supply end, Vbe is the conduction voltage of the triode V2, and Vcmp1 is the maximum value of the reference voltage.

According to the power-off restart automatic control circuit provided by the invention, the complete power-off restart of the whole hardware circuit board is controlled through a small number of components, and the power-off duration time is adjustable, so that the manual power-off restart operation is reduced, and the failure rate of the circuit board is reduced.

Drawings

The above and other features, properties and advantages of the present invention will become more apparent from the following description of the embodiments with reference to the accompanying drawings in which like reference numerals denote like features throughout the several views, wherein:

FIG. 1 discloses a functional block diagram of a power-down restart auto-control circuit according to an embodiment of the present invention;

FIG. 2 discloses a schematic diagram of a power-down restart auto-control circuit according to an embodiment of the present invention;

FIG. 3 discloses a timing diagram of the key signals of the power-down restart auto-control circuit according to an embodiment of the present invention.

The meanings of the reference symbols in the figures are as follows:

100 hardware circuit boards;

200 charge-discharge loop module;

300 comparing the circuit module;

400 a switching circuit module;

500 a power supply module;

501 power conversion unit.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The invention relates to the field of electronic products, in particular to an unattended electronic product which runs for a long time.

The power-off restarting automatic control circuit provided by the invention can enable the inside of the whole hardware circuit board to be reset in a power-off mode, and can adjust the power-off duration time.

Fig. 1 discloses a schematic block diagram of a power-off restart automatic control circuit according to an embodiment of the present invention, and as shown in fig. 1, the power-off restart automatic control circuit provided in the present invention is used for controlling power-off restart of a hardware circuit board 100, and includes a charging and discharging loop module 200, a comparison circuit module 300, a switch circuit module 400, and a power supply module 500.

The hardware circuit board 100 is connected to the charge and discharge circuit module 200.

The hardware circuit board 100 sends a power-off reset signal to the charge and discharge circuit module 200 to control the charge and discharge circuit module 200 to charge and discharge.

The charge and discharge circuit module 200 is connected to the comparison circuit module 300, and outputs a charge voltage or a discharge voltage as a comparison voltage to the comparison circuit module 300.

The comparison circuit module 300 is connected to the switch circuit module 400, compares the comparison voltage with the reference voltage, outputs a switch off signal or a switch on signal, and controls the switch circuit module 400 to be turned off or on.

The charging voltage and the discharging voltage of the charging and discharging circuit module 200 are used as comparison voltages of the comparison circuit module 300, and are compared with the reference voltage of the comparison circuit module 300, so as to control the comparison circuit module 300 to output a switch off signal and a switch on signal.

The switch circuit module 400 is connected to the power module 500, and controls the circuit of the switch circuit module 400 to be turned off or on according to the switch off signal or the switch on signal, and controls whether the power module 500 supplies power to the hardware circuit board 100.

Fig. 2 discloses a schematic diagram of a power-off restart automatic control circuit according to an embodiment of the present invention, and the circuit composition structure of each module is specifically described below with reference to fig. 1 and fig. 2.

The power supply voltage of the hardware circuit board 100 is VCC _1 to VCC _ n, the signal ctrl is a power-off reset signal output by an internal processor or a watchdog circuit of the hardware circuit board 100, and the power-off reset signal is pulled down to a low level by a fourth resistor R4 of the charge-discharge loop module 200.

The charge and discharge circuit module 200 includes a fourth resistor R4, a fifth resistor R5, a diode V1, a sixth resistor R6, and a first capacitor C1:

one end of the fourth resistor R4 is connected to the ctrl of the hardware circuit board 100, and the other end is grounded to GND;

one end of the fifth resistor R5 is connected to the power-off reset signal end ctrl of the hardware circuit board 100, and the other end is connected to the anode of the diode V1;

the cathode of the diode V1 is connected to the comparison voltage input terminal Vctrl of the comparison circuit module 300;

one end of the sixth resistor R6 is connected with the cathode of the diode V1, and the other end of the sixth resistor R6 is grounded GND;

one end of the first capacitor C1 is connected to the cathode of the diode V1, and the other end is grounded to GND.

The comparison circuit module 300 comprises a comparator N1A, a first resistor R1, a second resistor R2 and a third resistor R3:

one end of the first resistor R1 is connected to the front-end power supply terminal VCC _ IN, and the other end is connected to pin 3 of the comparator N1A, i.e., the reference voltage input terminal Vcmp;

one end of the second resistor R2 is connected to pin 3 of the comparator N1A, i.e., the reference voltage input terminal Vcmp, and the other end is grounded GND;

the third resistor R3 has one end connected to pin 3 of the comparator N1A, i.e., the reference voltage input terminal Vcmp, and the other end connected to pin 1 of the comparator N1A, i.e., the output voltage output terminal Vo.

The pin 2 of the comparator N1A, i.e., the comparison voltage input terminal Vctrl, is connected to the negative electrode of the diode V1 of the charge-discharge loop module 200.

The power module 500 includes a front-end power supply terminal VCC _ IN and a power conversion unit 501.

The front-end power supply terminal VCC _ IN supplies power to the front end of the whole circuit all the time.

The power conversion unit 501 has one end connected to the switch circuit module 400 and the other end connected to the hardware circuit board 100, and converts the voltage VCC input from the switch circuit module 400 into the supply voltage VCC _1 to VCC _ n applicable to the hardware circuit board 100.

The switch circuit module 400 includes a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a transistor V2, and a field effect (MOS) transistor V3:

one end of the seventh resistor R7 is connected to the front end power supply terminal VCC _ IN, and the other end is connected to pin 1 of the comparator N1A of the comparison circuit module 300, i.e., the output voltage output terminal Vo;

one end of the eighth resistor R8 is connected with a pin 1 of the comparator N1A, the output voltage output end Vo is connected, and the other end of the eighth resistor R8 is connected with the base electrode of the triode V2;

an emitter of the triode V2 is grounded GND, and a collector of the triode V2 is connected with one end of a ninth resistor R9;

the other end of the ninth resistor R9 is connected with a front-end power supply terminal VCC _ IN;

the source electrode of the field effect transistor V3 is connected with a front end power supply terminal VCC _ IN, the grid electrode is connected with the collector electrode of the triode V2, the drain electrode is connected with the power supply conversion unit 501, and the drain electrode outputs voltage VCC.

The operation principle of the power-off restart automatic control circuit of the present invention is described below with reference to fig. 1 and 2.

When the hardware circuit board 100 normally works, the ctrl signal at the power-off reset signal terminal defaults to a low level, and the ctrl signal is reset to be valid at a high level.

When the hardware circuit board 100 normally works, the power-off reset signal crtl is at a low level, the comparison voltage input terminal Vctrl of the comparator N1A is at a low level, the comparison voltage Vcrtl is smaller than the reference voltage Vcmp1 of the pin 3 of the comparator N1A, the pin 1 output terminal of the comparator N1A is at a high impedance, and the output voltage Vo is pulled up to a high level through the seventh resistor R7 to be a switch conducting signal.

At this time, the bias voltage Vbe of the transistor V2 is forward biased on, and the bias voltage Vsg of the MOS transistor V3 is forward biased on.

The front end power supply terminal VCC _ IN outputs a voltage VCC through the drain of the MOS transistor V3, and the power conversion unit 501 converts the voltage VCC into the power supply voltages VCC _1 to VCC _ n of the hardware circuit board 100, and normally inputs the power supply voltages VCC _1 to VCC _ n into the hardware circuit board 100, so that the hardware circuit board 100 normally operates.

The charge and discharge loop module 200 charges after receiving the power-off reset signal ctrl, and when the charging voltage is higher than the reference voltage of the comparison circuit module 300, the comparison circuit module 300 outputs a switch-off signal

When the power-off reset signal ctrl is at a high level, the control hardware circuit board 100 is powered off, and the power-off reset signal ctrl inside thereof becomes at a low level.

When the power-off reset signal crtl is at a high level, the fifth resistor R5 of the charge and discharge circuit module 200 and the first capacitor C1 form an RC charge circuit, and the charge and discharge circuit module 200 is charged.

When the charging voltage Vcrtl is higher than the reference voltage Vcmp1 of pin 3 as the comparison voltage of the comparator N1A, the output voltage Vo of pin 1 of the comparator N1A is at a low level, and the switch turns off the signal.

At this time, the transistor V2 is turned off, the MOS transistor V3 is turned off, the power module 500 cannot supply power to the hardware circuit board 100, and no power is supplied to the hardware circuit board.

The charging and discharging circuit module 200 discharges after the hardware circuit board 100 is powered off, and when the discharging voltage is lower than the reference voltage of the comparison circuit module 300, the comparison circuit module 300 outputs a switch conducting signal.

After the hardware circuit board 100 is powered off, the second resistor R2 is connected in parallel with the third resistor R3, so that the reference voltage of the pin 3 of the comparator N1A is reduced to Vcmp2, and hysteresis comparison is performed.

The sixth resistor R6 of the charge and discharge circuit module 200 and the first capacitor C1 form an RC discharge circuit, and the charge and discharge circuit module 200 discharges.

The diode V1 is used to isolate the current from discharging from the fifth resistor R5 and the fourth resistor R4.

When the discharging voltage Vcrtl, which is the comparison voltage of the comparator N1A, is slowly discharged until the voltage is lower than the reference voltage Vcmp2, the output voltage Vo of the voltage pin 1 of the comparator N1A becomes a high level, which is a switch on signal.

At this time, the transistor V2 is turned on, the MOS transistor V3 is turned on, and the hardware circuit board 100 is normally powered.

The principle of the hysteresis comparison of the comparator is explained below.

Assuming two input signals of a forward terminal (+) and a reverse terminal (-) of the comparator, a forward terminal voltage V + is a reference voltage, and a reverse terminal voltage V-is a comparison voltage:

when the forward end voltage V + is higher than the reverse end voltage V-, the output is high resistance or high level;

when the forward end voltage V + is lower than the reverse end voltage V-, the output is low level;

when no hysteresis comparison is carried out, the reference voltage V + is fixed, if V + is 2V, the comparison voltage V-is higher than 2V and the output is low level, and the comparison voltage V-is lower than 2V and the output is high level;

when the hysteresis comparison is performed, the reference voltage V + will change,

assuming that V + is initially 2V, when V-is higher than V +, the output is low, making the reference voltage V + lower, and assuming that V + becomes 1V, V-needs a lower voltage, i.e., lower than 1V, before the output will flip to high.

The reference voltage of pin 3 of the comparator N1A is lowered after the power of the hardware circuit board 100 is cut off, so that the comparison is delayed.

Fig. 3 is a timing diagram of key signals of the power-down restart auto-control circuit according to an embodiment of the invention, as shown in fig. 3, the charging time t1 is a time for controlling the power-down action, the power-down reset signal ctrl is high, and is not immediately powered down, after the time t1, the charging voltage Vctrl is higher than the reference voltage Vcmp, and the duration of the power-down action is only related to the discharging time t 2. The voltage VCC is a voltage input to the power conversion unit 501.

The charging time of the charge-discharge loop module is proportional to the product of the fifth resistor R5 and the first capacitor C1, and the charging time t1 can be estimated from R5 × C1.

Assuming that the fifth resistor R5 is 1k Ω and the first capacitor C1 is 100uF, the charging time t1 is about 100 ms;

the discharge time of the charge-discharge loop module is proportional to the product of the sixth resistor R6, the first capacitor C1 and the reference voltage threshold Vh.

The discharge time t2 can be estimated from the reference voltage threshold Vh and R6 XC 1.

Assuming that Vh is 20% of the maximum value of charging voltage Vctrl and sixth resistor R6 is 1M Ω, discharge time t2 is about 1 × 100 × 0.2 — 20 s.

The difference between the maximum value and the minimum value of the reference voltage is a reference voltage threshold value, the larger the reference voltage threshold value Vh is, the longer the power-off duration is, and the calculation formula is as follows:

the 3-pin input current of comparator N1A is very small and negligible.

According to kirchhoff's current law, when the power-off reset signal ctrl is at a low level, there are:

thereby obtaining the maximum value of the reference voltage

When the power-off reset signal crtl is at a high level, the output voltage Vo of the comparator N1A becomes 0, and there are:

thereby obtaining the minimum value of the reference voltage

Thus, it is possible to prevent the occurrence of,

where Vo is the output voltage of comparator N1A.

The output voltage Vo of the comparator N1A is calculated as follows.

When the power-off reset signal ctrl is low, pin 1 of the comparator N1A is high-impedance, the input current is negligible, and according to kirchhoff's current law:

obtaining by solution:

VCC _ IN is the voltage value of the front-end power supply end and is a known quantity;

vbe is the turn-on voltage of transistor V2, which is a known quantity;

vcmp1 is the maximum value of the reference voltage;

the resistance value may be a commonly used numerical value.

According to the power-off restart automatic control circuit provided by the invention, the complete power-off restart of the whole hardware circuit board is controlled through a small number of components, and the power-off duration time is adjustable, so that the manual power-off restart operation is reduced, and the failure rate of the circuit board is reduced.

While, for purposes of simplicity of explanation, the methodologies are shown and described as a series of acts, it is to be understood and appreciated that the methodologies are not limited by the order of acts, as some acts may, in accordance with one or more embodiments, occur in different orders and/or concurrently with other acts from that shown and described herein or not shown and described herein, as would be understood by one skilled in the art.

As used in this application and the appended claims, the terms "a," "an," "the," and/or "the" are not intended to be inclusive in the singular, but rather are intended to be inclusive in the plural unless the context clearly dictates otherwise. In general, the terms "comprises" and "comprising" merely indicate that steps and elements are included which are explicitly identified, that the steps and elements do not form an exclusive list, and that a method or apparatus may include other steps or elements.

The embodiments described above are provided to enable persons skilled in the art to make or use the invention and that modifications or variations can be made to the embodiments described above by persons skilled in the art without departing from the inventive concept of the present invention, so that the scope of protection of the present invention is not limited by the embodiments described above but should be accorded the widest scope consistent with the innovative features set forth in the claims.