JP6029520B2 - Power supply monitoring apparatus and power supply monitoring method - Google Patents

Description

  The present invention relates to a power supply monitoring device that shuts off a power supply device from a load device when an overvoltage and an undervoltage of the power supply device are detected, and in particular, can diagnose a voltage monitoring circuit while maintaining power supply to the load device. The present invention relates to a power monitoring apparatus and a power monitoring method that can be performed.

  As a processing procedure of a typical representative power supply monitoring device, first, when a drop in the power supply voltage is detected, the voltage monitoring circuit outputs an abnormal signal such as a reset signal to the load device. Some load devices such as the microcomputer of the load device that has received the abnormal signal perform processing in a procedure of stopping the operation of the load device itself (see, for example, Patent Document 1).

  Further, in the power supply monitoring device of Patent Document 1, a voltage monitoring circuit diagnostic circuit for enabling the voltage monitoring circuit to reliably detect a drop in the power supply voltage and output an abnormal signal to the load device is provided. I have.

JP 2012-3565 A

However, the prior art has the following problems.
In the power supply monitoring device of Patent Literature 1, the voltage monitoring circuit only outputs an abnormal signal to the load device when detecting an abnormality in the power supply voltage. Therefore, the power supply line of the load device remains connected to the power supply device, and there is a problem that the load device cannot be physically protected from an abnormality in the power supply voltage.

  In order to solve this problem, the power supply device may be completely disconnected from the load device when a drop in the power supply voltage is detected.

  However, in order to self-diagnose a voltage monitoring circuit having such a power shutoff function, it is necessary to confirm that the power supply device is shut off from the load device by forcibly reducing the power supply voltage. For this reason, there is a problem in convenience that the power supply to the load device must be stopped every time the self-diagnosis is performed.

  Moreover, in the power supply monitoring apparatus of patent document 1, although the fall of a power supply voltage can be detected, an overvoltage cannot be detected. As a result, there is a reliability problem that the load device cannot be protected from the overvoltage of the power supply device.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a power monitoring device and a power monitoring method excellent in reliability and convenience that can protect a load device from overvoltage and low voltage. And

  A power supply monitoring apparatus according to the present invention is a power supply monitoring apparatus that is installed between a power supply apparatus and a load apparatus and monitors a power supply voltage supplied from the power supply apparatus to the load apparatus, and includes a power output terminal of the power supply apparatus and a load A first power supply line and a second power supply line that are connected in parallel to connect a power input terminal of the apparatus, and a power output terminal of the power supply apparatus and a power input terminal of the load apparatus that are inserted in series with the first power supply line. The first switch that switches the connection to the ON state or OFF state and the second power supply line are inserted in series, and the connection between the power supply output terminal of the power supply device and the power supply input terminal of the load device is ON state or OFF state A first switch and a second resistor whose resistance values can be changed by an external command, and the power supply voltage output from the power supply device is output using the first resistor and the second resistor. By dividing the voltage, The reference voltage generation circuit for generating the reference voltage and the reference voltage output by the reference voltage generation circuit are monitored, and when the overvoltage or the undervoltage of the reference voltage is detected, the power supply device is turned off by switching the first switch to the OFF state. An external command is issued to the reference voltage generation circuit in a state in which the power supply to the load device is maintained by switching the second switch to the ON state in advance by turning on the second switch in advance to turn off the power supply from the load device. When the first resistance value or the second resistance value is changed by outputting to generate an overvoltage state or an undervoltage state of the reference voltage in a pseudo manner, the first voltage value is generated when the overvoltage state or the undervoltage state is generated. Voltage monitoring circuit self-diagnosis for diagnosing whether or not the power cutoff function by the voltage monitoring circuit is normally implemented by confirming the change of the first feedback voltage from the power line In which and a diagnostic circuit for implementing the ability.

  The power monitoring method according to the present invention is a power monitoring method used in the power monitoring device according to the present invention, and the diagnostic circuit implements the voltage monitoring circuit self-diagnosis function while maintaining the power supply to the load device. Therefore, by changing the first resistance value or the second resistance value by outputting an external command to the reference voltage generation circuit in the first step of switching the second switch to the ON state in advance, A second step of artificially generating an overvoltage state or an undervoltage state of the reference voltage, and confirming a change in the first feedback voltage from the first power supply line when the overvoltage state or the undervoltage state is generated; Thus, there is a third step of diagnosing whether or not the voltage monitoring circuit power supply cutoff function is normally implemented.

  According to the present invention, it is possible to diagnose a voltage monitoring circuit that shuts off the power supply device from the load device when an overvoltage and an undervoltage of the power supply device are detected, and that maintains the power supply to the load device. By providing the diagnostic circuit, it is possible to obtain a power monitoring device and a power monitoring method excellent in reliability and convenience that can protect the load device from overvoltage and low voltage.

It is an illustration figure of the system configuration | structure using the power supply monitoring apparatus, power supply device, and load apparatus in Embodiment 1 of this invention. It is an illustration figure of the circuit structure of the power supply monitoring apparatus in Embodiment 1 of this invention. It is an illustration figure of the circuit structure of the reference voltage generation circuit of the power supply monitoring apparatus in Embodiment 1 of this invention. It is a figure which shows the operation | movement and state of the reference voltage generation circuit in Embodiment 1 of this invention. It is a figure which shows the operation | movement and state of the power supply monitoring apparatus in Embodiment 1 of this invention.

  Hereinafter, preferred embodiments of a power monitoring apparatus and a power monitoring method according to the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected and demonstrated about the part which is the same or it corresponds in each figure.

Embodiment 1 FIG.
FIG. 1 is an exemplary diagram of a system configuration using a power supply monitoring device 1, a power supply device 2, and a load device 3 according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the power supply monitoring device 1 according to the first embodiment is installed between the power supply device 2 and the load device 3 and monitors the voltage supplied from the power supply device 2 to the load device 3. . And when the overvoltage and the undervoltage of the power supply device 2 are detected, it has the function which interrupts | blocks the power supply device 2 from the load apparatus 3 (henceforth this function is called a power supply cutoff function).

  Further, the power supply monitoring device 1 according to the first embodiment has a function capable of diagnosing whether or not the power cut-off function functions normally while maintaining the power supply to the load device 3 (hereinafter, referred to as “power-off function”). This function is called a self-diagnosis function).

  FIG. 2 is an exemplary diagram of a circuit configuration of the power supply monitoring device 1 according to the first embodiment of the present invention.

  The power supply monitoring apparatus 1 according to the first embodiment is configured by multiplexing power supply monitoring apparatuses 1 having the same circuit configuration. In FIG. 2, the numerals in parentheses indicate the multiplexing system numbers. For example, in FIG. 2, the power supply monitoring device 1 is duplicated, and includes a system (1) and a system (2).

  As described above, by multiplexing the power monitoring apparatuses 1, even when the power monitoring apparatus 1 of a specific system does not function normally due to a failure or the like, the function is substituted by the power monitoring apparatus 1 of another system. As a result, the reliability of the power supply monitoring device 1 can be improved.

  The power supply monitoring device 1 shown in FIG. 2 includes a first power supply line L1, a second power supply line L2, reference voltage generation circuits 11 (1) and 11 (2), and voltage monitoring circuits 12 (1) and 12 (2 ), Diagnostic circuits 13 (1), 13 (2), first switches Sw1 (1), Sw1 (2), second switches Sw2 (1), Sw2 (2), first diode D1, second The diode D2 and diagnostic circuit communication means 4 are provided.

  From here, the operation of the power supply monitoring device 1 according to the first embodiment will be described in more detail with reference to FIG. 2, but the circuit configuration of the power supply monitoring device 1 is the same in any multiplexed system. The description will be made taking the case of the system (1) as an example. Moreover, the system number which is a notation of the reference numerals in parentheses is omitted unless particularly necessary.

  First, the power cutoff function by the voltage monitoring circuit 12 will be described.

  The power supply output terminal of the power supply device 2 and the power supply input terminal of the load device 3 are electrically connected by a first power supply line L1 and a second power supply line L2 that are arranged in parallel.

  The first power supply line L1 has a first switch Sw1 inserted in series, and the second power supply line L2 has a second switch Sw2 inserted in series. In order for power to be supplied from the power supply device 2 to the load device 3, it is sufficient that either the first switch Sw1 or the second switch Sw2 is ON.

  During normal operation, the first switch Sw1 is ON and the second switch Sw2 is OFF. That is, the first power supply line L1 is used as a power supply line during normal operation. On the other hand, the second power supply line L2 is used as a bypass power supply line when a self-diagnosis function of the voltage monitoring circuit 12 by the diagnostic circuit 13 described later is performed.

  The first diode D1 provided in the first power supply line L1 prevents current from flowing from the second power supply line L2 to the first power supply line L1. Similarly, the second diode D2 provided in the second power supply line L2 prevents a current from flowing from the first power supply line L1 to the second power supply line L2.

  Next, FIG. 3 is an exemplary diagram of a circuit configuration of the reference voltage generation circuit 11 of the power supply monitoring device 1 according to the first embodiment of the present invention. FIG. 3 shows the system (1) of the multiplexed reference voltage generation circuit 11 of the power supply monitoring device 1.

  The reference voltage generation circuit 11 shown in FIG. 3 is configured by connecting a first resistor R1 and a second resistor R2 in series. The first resistor R1 is configured by connecting a resistor R1a and a resistor R1b in parallel, and the second resistor R2 is configured by connecting a resistor R2a and a resistor R2b in parallel. Further, a third switch Sw3 and a fourth switch Sw4 are inserted in series in the resistor R1b and the resistor R2b, respectively, and the third switch Sw3 and the fourth switch Sw4 are connected to the diagnostic circuit 13. Yes.

  The reference voltage generation circuit 11 generates the reference voltage V1 by dividing the power supply voltage V2 with the first resistor R1 and the second resistor R2. The reference voltage V1 can be set to an arbitrary value that is equal to or lower than the power supply voltage V2 by adjusting the values of the first resistor R1 and the second resistor R2.

  The third switch Sw3 and the fourth switch Sw4 are turned on / off by a diagnostic circuit 13 described later, and both are turned off during normal operation.

  When the power supply voltage V2 becomes overvoltage or undervoltage, the reference voltage V1 becomes overvoltage or undervoltage at the same ratio. The voltage monitoring circuit 12 constantly monitors the reference voltage V1, and when the overvoltage or undervoltage of the reference voltage V1 is detected, the power supply device 2 is disconnected from the load device 3 by turning off the first switch Sw1.

  Thus, the voltage monitoring circuit 12 does not directly monitor the power supply voltage V2, but indirectly monitors the divided reference voltage V1, as will be described later, the diagnostic circuit 13 monitors the voltage. This is because when the self-diagnosis function of the circuit 12 is performed, the reference voltage V1 can be changed to an overvoltage state or an undervoltage state in a pseudo manner.

  Specifically, when the third switch Sw3 is turned ON, the first resistance R1 that was R1a when OFF is reduced to (R1a × R1b) / (R1a + R1b) <R1a, and the reference voltage V1 is pseudo Overvoltage condition occurs. Similarly, when the fourth switch Sw4 is turned ON, the reference voltage V1 becomes a pseudo low voltage state.

  The resistor R1b and the resistor R2b may be any resistor as long as the resistor R1a> the resistor R1b and the resistor R2a> the resistor R2b are satisfied.

  Next, the self-diagnosis function of the voltage monitoring circuit 12 by the diagnostic circuit 13 will be described.

  The diagnosis circuit 13 turns on the second switch Sw2 in advance before starting the diagnosis of the power cutoff function of the voltage monitoring circuit 12. Thereby, even if the first switch Sw1 is turned off by the voltage monitoring circuit 12 during diagnosis, the power supply to the load device 3 can be maintained.

  When the power cutoff function of the voltage monitoring circuit 12 is implemented, the diagnostic circuit 13 sets the reference voltage control signal S1a to the H level and turns on the third switch Sw3 to thereby set the value of the first resistor R1. And an overvoltage state of the reference voltage V1 is generated in a pseudo manner. Alternatively, the diagnostic circuit 13 sets the reference voltage control signal S1b to the H level and turns on the fourth switch Sw4, thereby changing the value of the second resistor R2 to reduce the reference voltage V1 in a pseudo manner. Generate an overvoltage condition.

  As a result, the voltage monitoring circuit 12 detects an overvoltage and an undervoltage of the reference voltage V1, and turns off the first switch Sw1. Then, the abnormality signal S2 is set to L level, and the fact that the reference voltage V1 is abnormal is output to an external device, for example, the load device 3.

  At this time, if the abnormal signal S2 may cause a malfunction of the external device, the abnormal signal S2 may be blocked during the execution of the self-diagnosis function. For example, a switch that can be controlled from the diagnostic circuit 13 is provided on the signal line of the abnormal signal S2, and is set to the H level during diagnosis.

  The diagnostic circuit 13 confirms whether or not the first feedback voltage V4 changes to the L level after forcibly changing the reference voltage V1, so that the power cutoff function of the voltage monitoring circuit 12 is normal. Whether or not can be diagnosed. At this time, it can also be confirmed whether or not the first power line L1 and the first switch Sw1 are normal.

  When the diagnosis circuit 13 confirms that the power shutoff function of the voltage monitoring circuit 12 is normal, the diagnostic circuit 13 returns the first switch Sw1 to ON, and then returns the second switch Sw2 to OFF. The self-diagnosis of the monitoring circuit 12 is finished.

  On the other hand, if the power monitoring function of the voltage monitoring circuit 12 cannot be confirmed to be normal, the diagnostic circuit 13 turns off the first switch Sw1 and the second switch Sw2 and loads the power supply device 2 to the load. By disconnecting from the device 3, the load device 3 is protected from overvoltage and undervoltage of the power supply device 2.

  In the multiplexed power supply monitoring apparatus 1, the second power supply line L2 functions as a bypass power supply line only when the second switches Sw2 of all the systems are ON. Therefore, the self-diagnosis function of the voltage monitoring circuit 12 needs to be implemented after turning on the second switches Sw2 of all the systems in advance.

  Further, in the multiplexed power supply monitoring apparatus 1, if the above self-diagnosis function is to be performed simultaneously in a plurality of systems, the power supply shutoff function is provided if at least one voltage monitoring circuit 12 in each system is normal. Therefore, it is impossible to distinguish which system voltage monitoring circuit 12 has implemented the power shut-off function only by confirming the first feedback voltage V4.

  Therefore, the power supply monitoring device 1 according to the first embodiment includes inter-diagnostic circuit communication means 4. Thereby, the diagnostic circuit 13 of each system adjusts the order and start timing of the self-diagnostic function in each system using the inter-diagnostic circuit communication means 4 so that the self-diagnosis function is not simultaneously performed in each system. . Also, the timing for simultaneously turning on / off the second switches Sw2 of all the systems is adjusted.

  Any method can be used to realize the inter-diagnostic circuit communication means 4 as long as the status can be shared by all the diagnostic circuits 13. For example, shared memory, parallel communication, serial communication, or a combination of these can be used.

  Next, the self-diagnosis function of the second power supply line L2 and the second switch Sw2 constituting the bypass circuit by the diagnosis circuit 13 will be described. Note that the self-diagnosis function of the bypass circuit is performed when the first switch Sw1 is ON.

  Whether or not the second switch Sw2 is normal is whether or not the second feedback voltage V5 follows and changes to the H level / L level when the second switch Sw2 is turned ON / OFF. Diagnosis can be made by checking. At the same time, it can be confirmed whether or not the second power supply line L2 is normal.

  When it is confirmed that the bypass circuit is normal, the diagnostic circuit 13 returns the second switch Sw2 to OFF and ends the self-diagnosis of the bypass circuit. On the other hand, when it cannot be confirmed that the bypass circuit is normal, the diagnostic circuit 13 turns off the first switch Sw <b> 1 and the second switch Sw <b> 2 and disconnects the power supply device 2 from the load device 3.

  In addition, in the multiplexed power supply monitoring device 1, it is confirmed by the following procedure that the function as a bypass circuit composed of the second power supply line L2 and the second switch Sw2 is normal, for example. can do.

  First, it is confirmed that when the second switches Sw2 of all the systems are simultaneously turned ON / OFF, the second feedback voltage V5 follows and changes to the H level / L level. Next, it is confirmed that the second feedback voltage V5 does not change even if the second switches Sw2 of each system are individually turned on / off in a state where the second switches Sw2 of all the systems are turned off. .

  Further, when the second switches Sw2 of each system are individually turned OFF / ON in the state where the second switches Sw2 of all the systems are turned on, the second feedback voltage V5 follows the L level. By confirming the change to the / H level, in addition to the function of the second switch Sw2 as a bypass circuit, the soundness of the individual second switches Sw2 can also be confirmed.

  In the case of diagnosing the bypass circuit, as in the case of diagnosing the power shutoff function, the order and start timing for diagnosing the second switch Sw2 in each system can be determined by using the inter-diagnostic circuit communication means 4. Can be adjusted. Further, the timing for simultaneously turning on / off the second switches Sw2 of all the systems can also be adjusted.

  Next, FIG. 4 is a diagram showing the operation and state of the reference voltage generation circuit 11 according to Embodiment 1 of the present invention.

  In a state where the power supply voltage V2 is normal as shown in FIG. 4A, the reference voltage generation circuit 11 generates a normal reference voltage V1. As a result, the voltage monitoring circuit 12 sets the abnormal signal S2 to the H level and outputs to the outside that the reference voltage V1 is normal.

  In the overvoltage self-diagnosis state shown in FIG. 4B, the reference voltage control signal S1a is set to the H level by the diagnosis circuit 13, so that the reference voltage generation circuit 11 makes the reference voltage V1 pseudo-overvoltage. Change to state. As a result, the voltage monitoring circuit 12 detects an overvoltage of the reference voltage V1, sets the abnormality signal S2 to L level, and outputs to the outside that the reference voltage V1 is abnormal.

  In the low voltage self-diagnosis state shown in FIG. 4 (3), the reference voltage control signal S1b is set to the H level by the diagnosis circuit 13, so that the reference voltage generation circuit 11 artificially reduces the reference voltage V1. Change to voltage state. As a result, the voltage monitoring circuit 12 detects a low voltage of the reference voltage V1, sets the abnormality signal S2 to the L level, and outputs to the outside that the reference voltage V1 is abnormal.

  In the state shown in FIG. 4 (4) where the power supply voltage V2 is not normal, the reference voltage generation circuit 11 generates the reference voltage V1 that is overvoltage or undervoltage at the same ratio as the power supply voltage V2. As a result, the voltage monitoring circuit 12 detects an overvoltage or an undervoltage of the reference voltage V1, sets the abnormality signal S2 to the L level, and outputs to the outside that the reference voltage V1 is abnormal.

  Next, FIG. 5 is a diagram illustrating an operation and a state of the power supply monitoring device 1 according to the first embodiment of the present invention. FIG. 5 shows the state of the system (1) among the states of the multiplexed power supply monitoring device 1.

  In the state where the power supply voltage V2 shown in FIG. 5 (1) is normal, the first switches Sw1 of all systems are ON, and the second switches Sw2 of all systems are OFF. That is, the power is supplied by the first power line L1.

  In the self-diagnosis state of the voltage monitoring circuit 12 shown in FIG. 5 (2), the diagnostic circuit 13 turns on the reference voltage control signal S1a or the reference voltage control after turning on the second switches Sw2 of all systems in advance. By setting the signal S1b to the H level, the reference voltage V1 is pseudo-overvoltage or undervoltage.

  As a result, the voltage monitoring circuit 12 detects an overvoltage or an undervoltage of the reference voltage V1, and turns off the first switch Sw1. The diagnostic circuit 13 can diagnose whether or not the power cutoff function by the voltage monitoring circuit 12 has been normally performed by checking whether or not the first feedback voltage V4 changes to the L level.

  In the self-diagnosis state of the bypass circuit shown in FIG. 5 (3), first, in a state where the second switches Sw2 of all the systems are turned off, the second switches Sw2 of each system are individually turned OFF / ON. Also, it is confirmed that the second feedback voltage V5 does not change. Next, when the second switches Sw2 of all the systems are turned ON / OFF simultaneously, it is confirmed that the second feedback voltage V5 follows and changes to the H level / L level.

  In the state shown in FIG. 5 (4) where the power supply voltage V2 is not normal, the reference voltage generation circuit 11 generates the reference voltage V1 that is overvoltage or undervoltage at the same ratio as the power supply voltage V2. As a result, the voltage monitoring circuit 12 detects an overvoltage or an undervoltage of the reference voltage V1, turns off the first switch Sw1, and disconnects the power supply device 2 from the load device 3.

  As described above, according to the first embodiment, the voltage monitoring circuit that shuts off the power supply device from the load device when the overvoltage and the undervoltage of the power supply device are detected, and the voltage monitoring while maintaining the power supply to the load device. A diagnostic circuit capable of diagnosing the circuit.

  As a result, it is possible to obtain a power monitoring device and a power monitoring method excellent in reliability and convenience that can protect the load device from overvoltage and low voltage.

  3 and 4 show examples in which semiconductor switches are used as the first switch Sw1, the second switch Sw2, the third switch Sw3, and the fourth switch Sw4. The switch is not limited to a semiconductor. For example, a mechanical contact such as a relay can be used.

  In the description of FIG. 1, the power supply monitoring device 1 is installed between the power supply device 2 and the load device 3, but the power supply monitoring device 1 is incorporated in the power supply device 2 or the load device 3. It is clear that the same effect can be obtained in the form.

  DESCRIPTION OF SYMBOLS 1 Power supply monitoring apparatus, 2 Power supply apparatus, 3 Load apparatus, 11 Reference voltage generation circuit, 12 Voltage monitoring circuit, 13 Diagnostic circuit, 4 Diagnostic circuit communication means, V1 reference voltage, V2 supply voltage, V3 load voltage, V4 1st Feedback voltage, V5 second feedback voltage, L1 first power line, L2 second power line, Sw1 first switch, Sw2 second switch, Sw3 third switch, Sw4 fourth switch, D1 First diode, D2 Second diode, S1, S1a, S1b Reference voltage control signal, S2 abnormal signal, R1 first resistor, R2 second resistor, R1a, R1b, R2a, R2b resistor.

Claims (5)

A power supply monitoring device installed between a power supply device and a load device and monitoring a power supply voltage supplied from the power supply device to the load device,
A first power line and a second power line arranged in parallel to connect a power output terminal of the power supply and a power input terminal of the load device;
A first switch that is inserted in series with the first power supply line, and switches a connection between the power supply output terminal of the power supply device and the power supply input terminal of the load device to an ON state or an OFF state;
A second switch that is inserted in series with the second power supply line, and switches a connection between the power output terminal of the power supply device and the power supply input terminal of the load device to an ON state or an OFF state;
By having a first resistor and a second resistor whose resistance values can be changed by an external command, and dividing the power supply voltage output by the power supply device using the first resistor and the second resistor. A reference voltage generation circuit for generating a reference voltage;
The reference voltage output from the reference voltage generation circuit is monitored, and when the overvoltage or undervoltage of the reference voltage is detected, the power supply device is disconnected from the load device by switching the first switch to an OFF state. A voltage monitoring circuit that implements a power-off function to shut off;
By switching the second switch to the ON state in advance and maintaining the power supply to the load device, the external command is output to the reference voltage generation circuit to output the first resistance value or the A second resistance value is changed to artificially generate an overvoltage state or an undervoltage state of the reference voltage, and when the overvoltage state or the undervoltage state is generated, the second voltage value from the first power supply line is changed. And a diagnostic circuit for performing a voltage monitoring circuit self-diagnosis function for diagnosing whether or not the power cutoff function by the voltage monitoring circuit is normally implemented by confirming a change in the feedback voltage of 1. . In the power supply monitoring device according to claim 1,
The diagnostic circuit confirms a change in the second feedback voltage from the second power supply line when the second switch is switched to an ON state or an OFF state, whereby the second switch and the A power supply monitoring device having a bypass circuit self-diagnosis function for diagnosing whether or not the second power supply line is normal. In the power supply monitoring device according to claim 1 or 2,
The power monitoring device is multiplexed,
The diagnostic circuit of each of the multiplexed systems includes information on the order and start timing when performing the voltage monitoring circuit self-diagnosis function or the bypass circuit self-diagnosis function, and all the multiplexed systems. Power supply monitoring apparatus further comprising inter-diagnostic circuit communication means for sharing information on the timing of switching the second switch to the ON state or OFF state at the same time among the diagnostic circuits of the multiplexed systems . In the power supply monitoring device according to any one of claims 1 to 3,
The first power supply line includes a first diode for preventing a current from flowing from the second power supply line to the first power supply line,
The power supply monitoring apparatus, wherein the second power supply line includes a second diode for preventing a current from flowing from the first power supply line to the second power supply line. A power supply monitoring method used in the power supply monitoring device according to claim 1,
In the diagnostic circuit,
In order to perform the voltage monitoring circuit self-diagnosis function while maintaining the power supply to the load device, a first step of switching the second switch to an ON state in advance;
By outputting the external command to the reference voltage generation circuit, the first resistance value or the second resistance value is changed, and the overvoltage state or the low voltage state of the reference voltage is simulated. A second step of generating
Whether the voltage monitoring circuit power supply cutoff function is normally implemented by checking the change of the first feedback voltage from the first power supply line when the overvoltage state or the low voltage state is generated. A power monitoring method comprising: a third step of diagnosing whether or not.

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