Power failure holding circuit and relay protection device

Abstract

The invention relates to a power failure holding circuit and a relay protection device, and belongs to the field of relay protection. Wherein the power-down holding circuit comprises a CPU power supply branch circuit of which one end is used for connecting a power supply module and the other end is used for connecting a CPU system, and the CPU power supply branch circuit is used for supplying power to the CPU system; the power failure monitoring circuit is used for sending a power failure warning signal to the CPU system when the external power supply fails, so that the CPU system stores data; and the super capacitor is connected between the positive electrode and the negative electrode of the CPU power supply branch and is used for charging when the CPU power supply branch works normally and discharging to supply power to the CPU system when the external power supply fails. According to the invention, the CPU system can continue to work for a period of time and store data under the condition of external power failure, the data is not easy to lose, the reliability of the data is improved, and the safe operation of the relay protection device is further improved.

Description

Technical Field

[0001] The invention relates to a power-off holding circuit and a relay protection device, belonging to the field of relay protection. Background Art

[0002] The relay protection device has a power module and a CPU system inside. The power module is used to power the CPU system and other loads inside the relay protection device (such as the input module and the output module). The external power supply is directly connected to the power module inside the relay protection device. The power module converts the voltage provided by the external power supply into a voltage that can be used in the relay protection device. Common power modules can convert 220 volts (V) into 24V, or 24V into 5V, etc.

[0003] When the external power supply is powered on normally, the power module supplies power to the CPU system normally, and the CPU system stores data and executes related instructions. However, due to extremely bad weather, temporary switching of phase voltage, or loose wiring, the external power supply of the relay often loses power, resulting in sudden power outages. Such emergencies can cause the CPU system to shut down abnormally, resulting in file damage, large amounts of data loss, and other problems, greatly affecting the safe operation of the relay protection device. Summary of the invention

[0004] The object of the present invention is to provide a power-off holding circuit and a relay protection device, so as to solve the problem in the prior art that a CPU system in a relay protection device is prone to lose data when an external power supply fails.

[0005] To achieve the above object, the solution of the present invention includes: A power-off holding circuit of the present invention comprises: a CPU power supply branch circuit which is used to connect a power module at one end and to connect a CPU system at the other end and is used to supply power to the CPU system; a power-off monitoring circuit which is used to send a power-off alarm signal to the CPU system when an external power supply fails so that the CPU system can save data; and a super capacitor which is connected between the positive and negative electrodes of the CPU power supply branch circuit and is used to charge when the CPU power supply branch circuit works normally and discharge to supply power to the CPU system when the external power supply fails.

[0006] Furthermore, a first switch tube is connected in series on the CPU power supply branch circuit, which is turned on when the external power supply is normal and turned off when the external power supply fails. The first switch tube divides the CPU power supply branch into a first line for connecting to the power module and a second line for connecting to the CPU system; The first line is also connected to the super capacitor through a unidirectional current limiting circuit to charge the super capacitor.

[0007] Furthermore, the on-off end of the first switch tube is connected in series to the CPU power supply branch; both sides of the on-off end of the first switch tube are also connected to the first voltage comparator respectively; When the potential of one end of the first switch tube connected to the power module is lower than the potential of one end of the first switch tube connected to the CPU system, the first voltage comparator controls the first switch tube to be turned off; otherwise, the first voltage comparator controls the first switch tube to be turned on.

[0008] Furthermore, a first diode connected in series on the positive busbar of the CPU power supply branch and directed toward the CPU system; The CPU power supply branch on the anode side of the first diode is also connected to the super capacitor through a unidirectional current limiting circuit to charge the super capacitor.

[0009] Furthermore, a voltage regulating circuit for adjusting the discharge voltage of the supercapacitor is provided on the output side branch of the supercapacitor for discharge; Also included is a voltage monitoring circuit for monitoring the discharge voltage; When the discharge voltage is less than the first preset value, the voltage monitoring circuit cuts off the discharge of the supercapacitor through the voltage adjustment circuit; The voltage adjustment circuit includes: a Boost circuit or a Buck-Boost circuit.

[0010] Furthermore, a second switch tube is connected in series on the output side of the voltage regulating circuit on the output side branch of the supercapacitor for discharging, which is used to be cut off when the external power supply is normally supplied and to be turned on when the external power supply fails.

[0011] Furthermore, the on-off end of the second switch tube is connected in series to the output side of the voltage adjustment circuit on the output side branch of the super capacitor for discharge; the two sides of the on-off end of the second switch tube are also connected to the second voltage comparator respectively; When the potential of one end of the second switch tube connected to the voltage adjustment circuit is lower than the potential of one end of the second switch tube connected to the CPU power supply branch, the second voltage comparator controls the second switch tube to be turned off; otherwise, the second voltage comparator controls the second switch tube to be turned on.

[0012] Furthermore, a second diode with a conduction direction pointing to the CPU system is connected in series on the output side of the voltage regulating circuit on the output side branch of the super capacitor for discharging.

[0013] Furthermore, the unidirectional current limiting circuit comprises: a current limiting circuit and a third diode connected in series, the conduction direction of which points to the super capacitor; The power-off monitoring circuit includes: a photocoupler.

[0014] A relay protection device of the present invention comprises: a power supply module, a CPU system and the power-off holding circuit as described above.

[0015] The beneficial effects of the present invention are as follows: as a pioneering invention, the present invention provides a power-off holding circuit and a relay protection device, which monitor the external power supply by using a power-off monitoring circuit, and send a power-off alarm signal to the CPU system when the external power supply is powered off, so that the CPU system can save data; at the same time, a super capacitor is used to supply power to the CPU system when the external power supply is powered off, so as to maintain the normal operation of the CPU system for a period of time, so that the CPU system can save data. By using the power-off monitoring circuit and the super capacitor in combination, the CPU system can operate normally for a period of time to save data when the external power supply is powered off, which improves the reliability of the data, and thus can make the operation of the relay protection device safer and more reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural schematic diagram of a power-off holding circuit provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0018] The idea of ​​the present invention is to use a power-off monitoring circuit to monitor the status of an external power supply, and when the external power supply fails, send a power-off alarm signal to the CPU system so that the CPU system can save data; at the same time, when the external power supply fails, a supercapacitor branch is used to supply power to the CPU system so as to maintain the normal operation of the CPU system for a period of time, so that the CPU system can save data.

[0019] An embodiment of a power-off holding circuit: Figure 1 is a schematic diagram of a power-off holding circuit provided by an embodiment of the present invention, such as Figure 1 As shown, the power-off holding branch includes: a CPU power supply branch with one end connected to the power module and the other end connected to the CPU system, which is used to power the CPU system; a power-off monitoring circuit used to send a power-off alarm signal to the CPU system when the external power supply fails, so that the CPU system can save data; and a super capacitor connected between the positive and negative electrodes of the CPU power supply branch, which is used to charge when the CPU power supply branch works normally and discharge to power the CPU system when the external power supply fails.

[0020] In order to concentrate the discharge voltage of the supercapacitor on powering the CPU system and prevent discharge to other loads, as an optional implementation, a first diode with a conduction direction pointing to the CPU system can be connected in series on the positive bus of the CPU power supply branch; in order to better prevent the backflow of voltage or current, reduce the power loss of the first diode, and improve the reliability of the supercapacitor supplying power to the CPU system, as another optional implementation, a first switch tube Q1 is connected in series on the CPU power supply branch for conducting when the external power supply is normal and cut off when the external power supply fails. The following is an example of the first switch tube Q1 connected in series on the CPU power supply branch.

[0021] The first switch tube Q1 may be a bipolar junction transistor (BJT), or a metal-oxide-semiconductor field-effect transistor (MOSFET), etc., and the present invention does not specifically limit this. In order to reduce the cost, conduction voltage drop and loss, the first switch tube Q1 is an N-channel MOS tube as an example for exemplary description. The first switch tube Q1 is a MOS tube with a body diode.

[0022] The first switch tube Q1 can be connected in series to the positive bus of the CPU power supply branch, or it can be connected in series to the negative bus of the CPU power supply branch. The present invention does not specifically limit this. The following will take the case where the first switch tube Q1 is connected in series to the positive bus of the CPU power supply branch as an example for exemplary description.

[0023] In order to make the on and off of the first switch tube Q1 more reliable, as an optional implementation, the power-off holding circuit may further include a first driver and a first voltage comparator. Since the first switch tube Q1 is a MOS tube, the first driver is a first MOS tube driver. The controlled end of the first switch tube Q1 is connected to the control end of the first voltage comparator through the first MOS tube driver, and the first voltage comparator is connected to both ends of the on and off ends of the first switch tube Q1.

[0024] When the first switch tube Q1 is an N-channel MOS tube, the source of the first switch Q1 is respectively connected to the output end of the power module and the first input end of the first voltage comparator, the drain of the first switch tube Q1 is respectively connected to the CPU system and the second input end of the first voltage comparator, the gate (i.e., the controlled end) of the first switch tube Q1 is connected to the output end of the first MOS tube driver, and the control end of the first MOS tube driver is connected to the control end of the first voltage comparator.

[0025] The first voltage comparator is used to compare the source potential and the drain potential of the first switch tube Q1. When it is compared that the source potential of the first switch tube Q1 is greater than the drain potential of the first switch tube Q1, the first comparator controls the first MOS tube driver to drive the first switch tube Q1 to turn on; when it is compared that the source potential of the first switch tube Q1 is less than the drain potential of the first switch tube Q1, the first comparator controls the first MOS tube driver to drive the first switch tube Q1 to turn off.

[0026] In order to concentrate the discharge voltage of the supercapacitor on powering the CPU system and prevent discharge to other loads, as an optional implementation, the positive plate of the supercapacitor is also connected to the line connecting the source of the first switch tube Q1 and the power module through a unidirectional current limiting circuit.

[0027] The unidirectional current limiting circuit includes a current limiting resistor (not shown) connected in series and a third diode (not shown) whose conduction direction points to the super capacitor.

[0028] In order to prevent the voltage of the supercapacitor from being unstable, the discharge voltage being too high or too low, and causing damage to the CPU system, as an optional implementation, a voltage adjustment circuit for adjusting the discharge voltage of the supercapacitor is provided on the output side branch of the supercapacitor for discharge.

[0029] The voltage adjustment circuit outputs a preset voltage value when the supercapacitor is charged, and adjusts the discharge voltage of the supercapacitor to a normal power supply voltage value that meets the CPU system when the supercapacitor is discharged.

[0030] Among them, the preset voltage value is less than the output voltage of the power module minus the conduction voltage drop of the device type connected in series on the CPU power supply branch. For example, if the device connected in series on the CPU power supply branch is a first diode, the preset voltage value is the output voltage of the power module minus the conduction voltage drop of the first diode; if the first switch tube Q1 is connected in series on the CPU power supply branch, the preset voltage value is the output voltage of the power module minus the conduction voltage drop of the first switch tube Q1. The setting value of the preset voltage value is less than the output voltage of the power module minus the conduction voltage drop of the device type connected in series on the CPU power supply branch, which can ensure that when the external power supply is normally supplied, the super capacitor is in a charged state and will not discharge outward.

[0031] The voltage adjustment circuit may be a Boost circuit or a Buck-Boost circuit, etc., and the present invention does not specifically limit this. The following description will be given by taking the Buck-Boost circuit as an example for illustrative explanation.

[0032] When the voltage regulation circuit is a Buck-Boost circuit, the input side of the Buck-Boost circuit is connected in parallel to both ends of the supercapacitor, the output side of the Buck-Boost circuit is connected to the line connecting the first switch tube Q1 and the CPU system, and the controlled end of the switch tube in the Buck-Boost circuit is connected to the PWM controller.

[0033] In order to prevent the supercapacitor from discharging too low and causing damage to the CPU system, and also to increase its service life, as an optional implementation, the power-off holding circuit also includes a voltage monitoring circuit.

[0034] As an optional implementation, the monitoring end of the voltage monitoring circuit is connected to the line connecting the first switch tube Q1 and the CPU system, and the control end of the voltage monitoring circuit is connected to the enable end of the voltage adjustment circuit. In order to monitor more accurately, as another optional implementation, the monitoring end of the voltage monitoring circuit is connected to the line between the super capacitor and the voltage adjustment circuit.

[0035] Among them, a first preset value is set inside the voltage monitoring circuit, and the first preset value is greater than the minimum value required for normal power supply of the CPU system, so that the voltage adjustment circuit can be turned off in time when the discharge voltage of the supercapacitor is low, reducing the output jitter of the voltage adjustment circuit caused by the discharge voltage of the supercapacitor being too low, causing the CPU system to work abnormally. When the voltage monitoring circuit detects that the discharge voltage of the supercapacitor is less than the first preset value, the voltage monitoring circuit cuts off the discharge of the supercapacitor through the voltage adjustment circuit.

[0036] In order to prevent the CPU system power supply voltage from being too high and the components from being damaged by the backflow of current, as an optional implementation, the output side branch of the supercapacitor used for discharge is connected to the line connecting the first switch tube Q1 and the CPU system through the voltage adjustment circuit and the second diode whose conduction direction points to the CPU system. In order to ensure that the backflow current does not enter the voltage adjustment circuit, as another optional implementation, the output side branch of the supercapacitor used for discharge is connected to the line connecting the first switch tube Q1 and the CPU system through the voltage adjustment circuit and the second switch tube Q2. The following is an exemplary description using the voltage adjustment circuit connected to the second switch tube Q2 as an example.

[0037] The second switch tube Q2 may be a BJT or a MOSFET, etc., which is not particularly limited in the present invention. In order to reduce cost, conduction voltage drop and loss, the second switch tube Q2 is an N-channel MOS tube as an example for exemplary description.

[0038] In order to make the conduction and cutoff of the second switch tube Q2 more reliable, as an optional implementation, the power-off holding circuit also includes: a second driver and a second voltage comparator. Since the second switch tube Q2 is a MOS tube, the second driver is a second MOS tube driver. The controlled end of the second switch tube Q2 is connected to the control end of the second voltage comparator through the second MOS tube driver, and the second voltage comparator is connected to both ends of the conduction and cutoff ends of the second switch tube Q2.

[0039] When the second switch tube Q2 is an N-channel MOS tube, the source of the second switch Q2 is respectively connected to the output end of the voltage adjustment circuit and the first input end of the second voltage comparator, the drain of the second switch tube Q2 is connected to the line connecting the first switch tube Q1 and the CPU system, the drain of the second switch tube Q2 is also connected to the second input end of the second voltage comparator, the gate (i.e., the controlled end) of the second switch tube Q2 is connected to the output end of the second MOS tube driver, and the control end of the second MOS tube driver is connected to the control end of the second voltage comparator.

[0040] The second voltage comparator is used to compare the source voltage and drain voltage of the second switch tube Q2. When it is compared that the source voltage of the second switch tube Q2 is greater than or equal to the drain voltage of the second switch tube Q2, the second comparator controls the second MOS tube driver to drive the second switch tube Q2 to turn on; when it is compared that the source voltage of the second switch tube Q2 is less than the drain voltage of the second switch tube Q2, the second comparator controls the second MOS tube driver to drive the second switch tube Q2 to turn off.

[0041] Wherein, the power-off monitoring circuit includes a photocoupler.

[0042] As an optional implementation, the monitoring end of the power failure monitoring circuit is connected to the line on the input side of the power module, and the output end of the power failure monitoring circuit is connected to the CPU system. As another optional implementation, the monitoring end of the power failure monitoring circuit is connected to the line on the output side of the power module, and the output end of the power failure monitoring circuit is connected to the CPU system. In the following, an exemplary description is given by taking the example that the monitoring end of the power failure monitoring circuit is connected to the line on the input side of the power module, and the output end of the power failure monitoring circuit is connected to the CPU system.

[0043] The photocoupler may be a photocoupler circuit or a photocoupler chip, which is not particularly limited in the present invention. In order to reduce the circuit volume and improve the integration, the following description will be made by taking the photocoupler being a photocoupler chip as an example.

[0044] When the optocoupler is an optocoupler chip, if it is stipulated that the power-off monitoring circuit outputs a low-level signal to the CPU system when it detects that the external power supply is normal, and outputs a high-level signal to the CPU system when it detects that the external power supply is powered off, and the high-level signal is a power-off alarm signal: the primary side of the optocoupler chip, that is, the side with the diode, the cathode of the diode is grounded, and the anode of the diode is connected to the input side line of the power module; the secondary side of the optocoupler chip, that is, the side with the transistor, the collector of the transistor is connected to the power supply, the emitter of the transistor is grounded through a resistor, and is connected to the CPU system.

[0045] If it is stipulated that the power-off monitoring circuit outputs a high-level signal to the CPU system when it detects that the external power supply is supplying normally, and outputs a low-level signal to the CPU system when it detects that the external power supply is powered off, and the low-level signal is a power-off alarm signal: the primary side of the optocoupler chip, that is, the side with the diode, the cathode of the diode is grounded, and the anode of the diode is connected to the input side line of the power module; the secondary side of the optocoupler chip, that is, the side with the transistor, the collector of the transistor is connected to the pull-up resistor and connected to the CPU system, and the emitter of the transistor is grounded.

[0046] The working principle of the power-off holding circuit is described below.

[0047] When the external power supply is normally supplied, the power module supplies power to multiple loads; at the same time, the first voltage comparator detects that the source potential of the first switch tube Q1 is higher than the drain potential of the first switch tube Q1, and the first voltage comparator drives the first switch tube Q1 to conduct by controlling the first MOS tube driver, and the power module supplies power to the CPU system through the first switch tube Q1. At this time, since the first switch tube Q1 is in the on state, the voltage monitoring circuit detects that the power supply voltage of the CPU system is greater than the first preset value, the voltage monitoring circuit controls the voltage adjustment circuit to work normally, and the voltage adjustment circuit outputs the preset voltage value. The preset voltage value output by the voltage adjustment circuit is output to the source of the second switch tube Q2. The drain potential of the second switch tube Q2 is equal to the drain potential of the first switch tube Q1. Since the preset voltage value is smaller than the drain potential of the first switch tube Q1, it is also smaller than the drain potential of the second switch tube Q2. Therefore, the second voltage monitoring circuit detects that the source potential of the second switch tube Q2 is smaller than the drain potential of the second switch tube Q2. The second MOS tube driver is controlled to drive the second switch tube Q2 to be cut off. At the same time, the power module also charges the super capacitor through the unidirectional current limiting circuit.

[0048] When the voltage output by the power module fluctuates, the drain potential of the first switch tube Q1 decreases. When the drain potential of the first switch tube Q1 decreases to the preset voltage value output by the voltage adjustment circuit, since the source potential of the first switch tube Q1 is greater than the drain potential, the first voltage comparator drives the first switch tube Q1 to continue to be turned on by controlling the first MOS tube driver, and the power module continues to supply power to the CPU system; at the same time, since the drain potential of the first switch tube Q1 decreases to the preset voltage value output by the voltage adjustment circuit, the source potential of the second switch tube Q2 will be greater than the drain potential. At this time, the second voltage comparator drives the second switch tube Q2 to be turned on by controlling the second MOS tube driver, and the super capacitor is in a discharging state, and the super capacitor will also provide the CPU system with the voltage required by the CPU system. If the voltage output by the power module further decreases, the source potential of the first switch tube Q1 will be less than the drain potential, and the first voltage comparator drives the first switch tube Q1 to be turned off by controlling the first MOS tube driver. At the same time, since the drain potential of the first switch tube Q1 is less than the preset voltage value output by the voltage adjustment circuit, the drain potential of the second switch tube Q2 will be less than the source potential. At this time, the second voltage comparator drives the second switch tube Q2 to continue to conduct by controlling the second MOS tube driver, and the super capacitor is in a discharge state. The super capacitor provides the CPU system with the voltage required by the CPU system. The CPU system is temporarily powered by the super capacitor, which reduces the safety hazards to the CPU system when the output voltage of the power module fluctuates, and ensures the stability of the power supply of the CPU system.

[0049] When the voltage output by the power module is restored, the first voltage comparator detects that the source potential voltage of the first switch tube Q1 is higher than the drain potential, and drives the first switch tube Q1 to conduct by controlling the first MOS tube driver. Since the source potential voltage of the first switch tube Q1 is higher than the drain potential, the drain potential of the second switch tube Q2 will be higher than the source potential. Therefore, the second voltage comparator drives the second switch tube Q2 to be cut off by controlling the second MOS tube driver, and the power module charges the super capacitor through the unidirectional current limiting circuit.

[0050] When the external power supply fails, the power failure monitoring circuit detects that the external power supply fails, and outputs a power failure alarm signal to the CPU system. When the CPU system receives the power failure alarm signal, it starts to save important data. At the same time, due to the power failure of the external power supply, the supercapacitor starts to supply power to the CPU system through the voltage adjustment circuit, which will cause the source potential of the first switch tube Q1 to be lower than the drain potential. At this time, the first voltage comparator drives the first switch tube Q1 to be cut off by controlling the first MOS tube driver. The source potential of the first switch tube Q1 is lower than the drain potential, which will cause the drain potential of the second switch tube Q2 to be lower than the source potential. The second voltage comparator drives the second switch tube Q2 to be turned on by controlling the second MOS tube driver. When the discharge voltage of the supercapacitor is less than the first preset value, the voltage monitoring circuit turns off the voltage adjustment circuit through the enable signal, the supercapacitor no longer supplies power to the outside, and the CPU system shuts down.

[0051] The embodiment of the present invention provides a power-off holding circuit, which uses a power-off monitoring circuit to monitor the external power supply. When the external power supply is powered off, a power-off alarm signal is sent to the CPU system to enable the CPU system to save data; at the same time, a super capacitor is used to supply power to the CPU system when the external power supply is powered off, so as to maintain the normal operation of the CPU system for a period of time, so that the CPU system can save data. By using the power-off monitoring circuit and the super capacitor in combination, the CPU system can operate normally for a period of time to save data when the external power supply is powered off, thereby improving the reliability of the data, and further ensuring the safety and reliability of the operation of the relay protection device.

[0052] An embodiment of a relay protection device: A relay protection device provided by an embodiment of the present invention includes a power supply module, a power-off holding circuit and a CPU system.

[0053] The power module is used to power the CPU system and other loads (such as input modules and output modules) inside the relay protection device. The external power supply is directly connected to the power module inside the relay protection device. The power module converts the voltage provided by the external power supply into a voltage that can be used in the relay protection device. Common power modules can convert 220 volts (V) into 24V, or 24V into 5V, etc. If the external power supply can directly match the voltage level inside the device, the power module can also be omitted.

[0054] Among them, the CPU system is the core part of the relay protection device, which is used to store data, execute related instructions, etc.

[0055] Among them, the power-off holding circuit can refer to the relevant description in the aforementioned "an embodiment of a power-off holding circuit", which will not be repeated here.

[0056] A relay protection device provided in an embodiment of the present invention can achieve the same beneficial effects as the aforementioned power-off holding circuit, which will not be described in detail here.

Claims

1. A power-off holding circuit, characterized in that: include: One end is used to connect to the power module, and the other end is used to connect to the CPU system, which is used to supply power to the CPU system. A power-off monitoring circuit for sending a power-off alarm signal to the CPU system when an external power supply fails, so that the CPU system can save data; a supercapacitor connected between the positive and negative electrodes of the CPU power supply branch, for charging when the CPU power supply branch is working normally, and discharging to supply power to the CPU system when the external power supply fails.

2. The power-off holding circuit according to claim 1, characterized in that: The CPU power supply branch is connected in series with a first switch tube which is turned on when the external power supply is normal and turned off when the external power supply fails; The first switch tube divides the CPU power supply branch into a first line for connecting to the power module and a second line for connecting to the CPU system; The first line is also connected to the super capacitor through a unidirectional current limiting circuit to charge the super capacitor.

3. The power-off holding circuit according to claim 2, characterized in that: The on / off end of the first switch tube is connected in series to the CPU power supply branch; both sides of the on / off end of the first switch tube are also connected to the first voltage comparator respectively; When the potential of one end of the first switch tube connected to the power module is lower than the potential of one end of the first switch tube connected to the CPU system, the first voltage comparator controls the first switch tube to be cut off; otherwise, the first voltage comparator controls the first switch tube to be turned on.

4. The power-off holding circuit according to claim 1, characterized in that: A first diode connected in series with the positive busbar of the CPU power supply branch and with the conducting direction pointing to the CPU system; The CPU power supply branch on the anode side of the first diode is also connected to the super capacitor through a unidirectional current limiting circuit to charge the super capacitor.

5. The power-off holding circuit according to claim 1, characterized in that: The output side branch of the super capacitor for discharging is provided with a voltage adjustment circuit for adjusting the discharge voltage of the super capacitor; Also included is a voltage monitoring circuit for monitoring the discharge voltage; When the discharge voltage is less than a first preset value, the voltage monitoring circuit cuts off the discharge of the supercapacitor through the voltage adjustment circuit; The voltage adjustment circuit includes: a Boost circuit or a Buck-Boost circuit.

6. The power-off holding circuit according to claim 5, characterized in that: A second switch tube is connected in series on the output side of the voltage regulating circuit on the output side branch of the super capacitor for discharging, which is used to cut off when the external power supply is normally powered and to turn on when the external power supply fails.

7. The power-off holding circuit according to claim 6, characterized in that: The on / off end of the second switch tube is connected in series to the output side of the voltage adjustment circuit on the output side branch of the super capacitor for discharge; both sides of the on / off end of the second switch tube are also connected to the second voltage comparator respectively; When the potential of one end of the second switch tube connected to the voltage adjustment circuit is lower than the potential of one end of the second switch tube connected to the CPU power supply branch, the second voltage comparator controls the second switch tube to be cut off; otherwise, the second voltage comparator controls the second switch tube to be turned on.

8. The power-off holding circuit according to claim 5, characterized in that: A second diode is connected in series on the output side of the voltage regulating circuit on the output side branch of the super capacitor for discharging, and the conduction direction of the second diode is directed toward the CPU system.

9. The power-off holding circuit according to any one of claims 2 to 4, characterized in that: The unidirectional current limiting circuit comprises: a current limiting circuit connected in series and a third diode whose conduction direction points to the super capacitor; The power-off monitoring circuit comprises: a photoelectric coupler.

10. A relay protection device, characterized in that: include: A power supply module, a CPU system, and a power-off holding circuit as claimed in any one of claims 1 to 9.

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