JPH11127065A - Short-circuit fault detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely detect faults in the short-circuit mode caused in a semiconductor switching element that turns on/off power supply regardless of a simple configuration. SOLUTION: One terminal of a resistor R9 connects to a power supply Vcc and the other terminal connects to ground via a series circuit consisting of a transistor(TR) Q5 that is conductive when no voltage is applied to a gate of a FET 1 and a TR Q3 that is conductive when a source level of the FET 1 rises. Furthermore, a normally closed contact RS connects between a positive terminal of a battery B and a drain of the FET 1, one terminal of an exciting coil RC connects to the positive terminal of the battery B and the other terminal connects to ground via a TR Q6. On the occurrence of a short-circuit fault in the FET 1, the level of a signal at the other terminal of the resistor R9 goes to low level, the normally closed contact RS is open to stop continuous power supply to a lamp L.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for supplying power from a power supply to a load, and more particularly to a short-circuit failure detection circuit for detecting a short-circuit mode failure occurring in a semiconductor switching element for turning on and off power supply. Things.

[0002]

2. Description of the Related Art In recent years, in a power supply circuit for supplying power from a battery to a load such as a motor or a lamp mounted on an automobile, a switch means for turning on / off the power supply has been replaced with a conventional mechanical electromagnetic relay. A device using a semiconductor switching element at the contact point has been proposed (for example, Japanese Patent Publication No. Hei 8-14598), whereby the circuit size and cost have been reduced.

[0003]

However, when a semiconductor switching element is used, a short-circuit mode failure may occur. In this case, power supply to the load is continued.

[0004] The present invention has been made in view of the above,
An object of the present invention is to provide a short-circuit failure detection circuit that reliably detects a short-circuit mode failure that occurs in a semiconductor switching element that turns on and off power supply with a simple configuration.

[0005]

The present invention has a control terminal, a first terminal connected to a power supply, and a second terminal grounded via a load. In a power supply circuit including a semiconductor switching element for turning on / off a connection between a first terminal and the second terminal, a first switch means that is turned on when the control signal is not input to the control terminal; Second switch means that is turned on when the potential of the second terminal rises;
A failure detection signal output unit that outputs a failure detection signal when both the first switch means and the second switch means are on (claim 1).

According to this configuration, when both the first switch means which is turned on when the control signal is not input to the control terminal and the second switch means which is turned on when the potential of the second terminal rises are both turned on. As a result, a failure detection signal is output when the semiconductor switching element has a short-circuit failure, whereby the short-circuit failure is reliably detected.

The short-circuit fault detecting circuit according to claim 1, further comprising high-level signal output means, and a resistance element, one end of said resistance element being connected to said high-level signal output means, and being connected to the other end of said resistance element. An end is grounded via a series circuit including the first switch means and the second switch means, and the failure detection signal output section is configured to output the failure detection signal from the other end of the resistance element. (Claim 2).

According to this configuration, one end of the resistance element is connected to the high-level signal output means, and the other end of the resistance element is connected to the first level.
The signal level output from the other end of the resistive element is grounded via the series circuit including the switch means and the second switch means, and the signal level output from the other end of the resistive element becomes the first switch means and the second switch means when the semiconductor switching element is short-circuited. Since both of the means are turned on, the level is low, and otherwise, the level is high. Therefore, when a short circuit fault occurs in the semiconductor switching element, a low level fault detection signal is output from the other end of the resistor element. Thus, a short-circuit failure is reliably detected.

Further, in the short-circuit fault detection circuit according to claim 1 or 2, the circuit is connected between the power supply and the first terminal, and is switched between an energization permitting state for permitting energization and an energization restriction state for restricting energization. And a circuit element control circuit for controlling the circuit element to the power supply restriction state when the failure detection signal is output from the failure detection signal output unit (claim 3).

According to this configuration, when the failure detection signal is output from the failure detection signal output unit, the circuit element is connected between the power supply and the first terminal, and can be switched between the energized state and the energized state. Is controlled to be in the power supply restriction state, when a short circuit fault occurs in the semiconductor switching element, the current flowing from the power supply to the load is reduced, and the load is protected.

The short-circuit fault detecting circuit according to claim 3, further comprising an electromagnetic relay having a normally closed contact and an exciting coil, wherein the normally closed contact forms the circuit element, and the circuit element control circuit includes the fault. A third switch unit that is turned on when the failure detection signal is output from the detection signal output unit, one end of the excitation coil is connected to the power supply, and the other end of the excitation coil is connected via the third switch unit; It is configured to be grounded (claim 4).

According to this configuration, a circuit element is formed by the normally closed contact of the electromagnetic relay, one end of the exciting coil of the electromagnetic relay is connected to the power supply, and the other end of the exciting coil is connected to the failure detection signal output unit from the failure detection signal output unit. When the semiconductor switching element is short-circuited, the third switch is turned on, so that the exciting current flows through the exciting coil, so that the exciting current flows normally. The closed contact is opened, the power supply from the power supply to the load is stopped, and the load is reliably protected.

Further, in the short-circuit fault detecting circuit according to claim 3, the circuit element is a positive temperature coefficient thermistor, and the resistance control circuit is provided with a heater disposed close to the positive temperature coefficient thermistor, and the fault detecting circuit. A third switch unit that is turned on when the failure detection signal is output from the signal output unit, one end of the heater is connected to the power supply, and the other end of the heater is grounded via the third switch unit. (Claim 5).

According to this configuration, the circuit element is a positive temperature coefficient thermistor, and one end of the heater disposed close to the positive temperature coefficient thermistor is connected to the power source, and the other end of the heater is detected by the failure detection signal output unit from the failure detection signal output unit. Since the third switching means is turned on when a signal is output and grounded via the third switching means, the third switching means is turned on when the semiconductor switching element is short-circuited, thereby causing a current to flow through the heater to generate heat. The resistance of the positive temperature coefficient thermistor is increased by the heat of the heater, and the current flowing from the power supply to the load is reduced, thereby protecting the load.

Further, in the short-circuit failure detecting circuit according to any one of claims 1 to 5, an informing means which operates when energized and informs a driver, and a signal level at the other end of the resistance element is low. And a fourth switch means that is turned on when the power supply is turned on. A series circuit including the notification means and the fourth switch means is connected between the high-level signal output means and the ground (claim 6).

According to this configuration, when the signal level at the other end of the resistance element becomes low, the fourth switch is turned on, whereby the high-level signal output is energized to the notifying means, whereby the semiconductor switching is performed. When a short-circuit fault occurs in the element, the notifying means operates to notify the driver of that.

[0017]

FIG. 1 is a circuit diagram of a first embodiment of a lamp control circuit to which a short-circuit fault detection circuit according to the present invention is applied. This lamp control circuit controls the power supply from the battery B of the automobile to the lamp L, and includes an N-channel MOS-FET as a semiconductor switching element.
(Hereinafter simply referred to as “FET”) 1, power supply circuit 2, switch drive circuit 3, switch control unit 4, electromagnetic relay RL,
Lamp switch SW, resistors R1 to R10, capacitor C
1, NPN transistors Q1, Q3 to Q5, PNP transistors Q2, Q6, and a Zener diode ZD.

Then, by detecting an increase in the source potential of the FET 1 when the gate potential of the FET 1 is at a low level, it is detected that a short-circuit fault has occurred in the FET 1.

The battery B is a lead storage battery that outputs a voltage of, for example, 12 VDC, and constitutes a power supply. Lamp L is
Headlamps, tail lamps, stop lamps, and other lamps mounted on vehicles are applied and constitute the load. The electromagnetic relay RL has a normally closed contact RS and an exciting coil RC.

The positive terminal of the battery B is a normally closed contact RS
Is connected to the drain (first terminal) of FET1 through
The source (second terminal) of the FET 1 is grounded via a lamp L. Positive terminal of battery B and electromagnetic relay R
One end of the exciting coil RC of the electromagnetic relay RL, the power supply circuit 2 and the switch drive circuit 3 are connected to a line connecting the normally closed contact RS of L.

The power supply circuit 2 is provided with, for example, a three-terminal regulator or a zener diode, generates a constant voltage V _cc (for example, 5 V in this embodiment) from the output voltage of the battery B, and outputs it from the output terminal. It constitutes signal output means. The switch drive circuit 3 is composed of, for example, a charge pump circuit, and generates an operating voltage of about 20 V from the output voltage of the battery B, that is, an operating voltage sufficient to turn on the FET 1 with a low on-resistance, and supplies the operating voltage to the gate (control terminal) of the FET 1 To be applied.

The lamp switch SW is used to instruct the turning on and off of the lamp L by being externally operated and turned on and off.
When the switch is off, a high level signal is input to the switch control unit 4.

The switch control section 4 comprises a CPU and the like.
When the lamp switch SW is turned on, the operating voltage is applied to the gate of the FET 1 by the switch driving circuit 3 to turn on the FET 1 to turn on the lamp L, and the lamp switch SW is turned on. When it is off, the application of the operating voltage is stopped, the FET1 is turned off, and the lamp L is turned off.

The source of FET1 further includes resistors R1, R
2 are grounded through a series circuit of two. Resistance R2
Is connected in parallel with a Zener diode ZD having a Zener voltage of about 5V. The connection point of the resistors R1 and R2 is
It is connected to the base of the transistor Q1 via the resistor R3.

The base of the transistor Q1 is further grounded via a capacitor C1, the emitter is grounded, and the collector is connected to an output terminal of the power supply circuit 3 (hereinafter referred to as "power supply _Vcc ") via a resistor R4. And is connected to the base of the transistor Q2.

The emitter of the transistor Q2 is connected to the power supply _Vcc , the collector is connected to the base of the transistor Q3, and is grounded via the resistor R5.

On the other hand, the gate of FET1 is connected to resistors R6, R
7 is grounded via a series circuit composed of 7 elements. Resistance R
6 and R7 are connected to the base of transistor Q4, the emitter of transistor Q4 is grounded, and the collector is connected to power supply V _CC via resistor R8.
It is connected to the base of transistor Q5. The emitter of the transistor Q5 is grounded, and the collector is connected to the emitter of the transistor Q3.

[0028] One end of the resistor R9 is connected to the power supply V _CC, the other end of the resistor R9 (in the figure, X point) is connected to the collector of the transistors Q3, is connected to the base of the transistor Q6. The collector of the transistor Q6 is grounded, and the emitter is an electromagnetic relay RL via a resistor R10.
Is connected to the other end of the exciting coil RC.

In such a circuit, the transistor Q
5 constitutes a first switch means, transistor Q3 constitutes a second switch means, transistor Q6 constitutes a third switch means, resistor R9 constitutes a resistance element, power supply V _CC , resistor R9, transistor Q3 , Q5 constitute a failure detection signal output unit.

Next, the operation will be described. In the steady state in which the lamp switch SW is off, no voltage is applied to the gate of the FET1, so that no base current is supplied via the resistor R6, and the transistor Q4 is off.
Therefore, the base current is supplied from the power supply V _CC via the resistor R8, and the transistor Q5 is turned on. When a gate voltage is applied to the FET 1 by turning on the lamp switch SW, the resistance R6 is applied by the gate voltage.
, A base current is supplied to turn on the transistor Q4. By turning on the transistor Q4, the base current is bypassed and the transistor Q5 is turned off.

On the other hand, FET1 is on, that is, FET1
When the source potentials of the resistors R1 and R3
Transistor Q1 is turned on base current is supplied through the, by the on of the transistor Q1, the power supply V _CC
Supplies a base current via a resistor R4 to turn on the transistor Q2. When the transistor Q2 is turned on, a base current is supplied from the power supply V _CC and the transistor Q3 is turned on.
Turns on.

Therefore, when the FET1 is on even though no gate voltage is applied to the FET1,
That is, when a short-circuit mode failure occurs in FET1, both transistors Q3 and Q5 are turned on.

As a result, the collector (point X in the figure) of the transistor Q3 goes low when a short-circuit mode fault occurs in the FET1, and goes high otherwise, so that the collector at the point X is based on the level at point X. Thus, a short-circuit failure of the FET 1 can be detected.

[0034] When the transistors Q3, Q5 are turned on both, the transistor Q6 is turned on by the base current flows from the power supply V _CC through a resistor R9, thereby to exciting current flows opens the normally closed contact RS , The current supply to the lamp L is stopped.

As described above, according to the first embodiment, one end of the resistor R9 is connected to the power supply V _cc , and the other end is turned on when no voltage is applied to the gate of the FET R1. Since the grounding is performed via the series circuit including the transistor Q3 which is turned on when the source potential is rising, the short-circuit failure of the FET1 based on the signal level at the other end of the resistor R9 is ensured with a simple configuration. Can be detected.

The positive terminal of battery B and FET1
And the other end of the exciting coil RC is connected to the positive terminal of the battery B, and the other end is grounded via the transistor Q6.
When a short-circuit fault occurs in the ET1, the signal level at the other end of the resistor R9 becomes low level, thereby opening the normally closed contact RS. Can be stopped.

FIG. 2 is a circuit diagram of a second embodiment of the lamp control circuit to which the short-circuit failure detection circuit according to the present invention is applied. The second embodiment is the electromagnetic relay RL of the first embodiment,
Instead of the resistor R10 and the transistor Q6, a resistor R1
1. It has a PNP transistor Q7 (fourth switch means) and a light emitting diode LED.

The emitter of the transistor Q7 is connected to a resistor R11.
_Is connected to the power supply V _CC through the
3 and the collector is a light emitting diode L
Connected to the anode of the ED, the light emitting diode LE
The cathode of D is grounded.

The light emitting diode LED is disposed, for example, on an instrument panel of an automobile, and informs a driver of a short-circuit failure occurring in the FET 1 and constitutes a notifying means.

The operation of the second embodiment will be described. F
When a short-circuit fault occurs in ET1 and both transistors Q3 and Q5 are turned on and point X goes to a low level, transistor Q7 is turned on and the light emitting diode LED is energized and emits light. A short-circuit fault is reported.

As described above, according to the second embodiment, a series circuit including the transistor Q7 and the light emitting diode LED which is turned on when the signal level at the other end of the resistor R9 becomes low level is connected to the high level signal output means and the ground. When a short-circuit fault occurs in the FET1, the light-emitting diode LED can be caused to emit light, whereby the driver can be notified of the short-circuit fault in the FET1, and the driver can detect the fault in the FET1. Can take countermeasures.

FIG. 3 is a circuit diagram of a third embodiment of a lamp control circuit to which the short-circuit failure detection circuit according to the present invention is applied. The third embodiment includes a light emitting diode LED instead of the resistor R10 and the transistor Q6 of the first embodiment.

In the third embodiment, the other end of the exciting coil RC is connected to the output terminal P1 of the switch controller 4, and the collector of the transistor Q3 is connected to the switch controller 4.
Is connected to the input terminal P2. The anode of the light emitting diode LED is connected to the output terminal P3 of the switch control unit 4 via a resistor.
Are grounded.

The switch control section 4 has the following functions (1) to (4). By determining the level of the input terminal P2, the FET
It is determined whether or not a short circuit fault has occurred in 1. When it is determined that a short circuit fault has occurred in the FET1, a low level signal is output from the output terminal P1. When it is determined that a short-circuit fault has occurred in the FET1, a high-level signal is output from the output terminal P3.

The operation of the third embodiment will be described. F
When a short-circuit fault occurs in ET1 and both the transistors Q3 and Q5 are turned on and the point X goes low, the switch controller 4 determines that a short-circuit fault has occurred in the FET1.

Then, the switch controller 4 applies an exciting current to the exciting coil RC to open the normally closed contact RS, thereby stopping the power supply to the lamp L due to the short-circuit of the FET 1 and turning off the light emitting diode LED. It emits light when energized, thereby informing the driver of the short-circuit failure of FET1.

As described above, according to the third embodiment, the short-circuit failure of the FET 1 can be detected using the switch control unit 4, and the power supply to the lamp L is stopped, and the short-circuit failure occurs to the driver. Can be reported.

FIG. 4 is a circuit diagram of a fourth embodiment of the lamp control circuit to which the short-circuit failure detection circuit according to the present invention is applied. In the fourth embodiment, a heater HE, a small amount of explosive IG and a fuse FU are used instead of the electromagnetic relay RL of the first embodiment.
It has.

In the fourth embodiment, the positive terminal of the battery B is connected to the drain (first
Terminal, and one end of the heater HE, a power supply circuit 2 and a switch drive circuit 3 are connected to a line connecting the positive terminal of the battery B and the fuse FU.
Is connected to the emitter of the transistor Q6 via the resistor R10.

The explosive IG is arranged close to the heater HE, and the fuse FU is arranged close to the explosive IG.

The operation of the fourth embodiment will be described. F
When a short-circuit fault occurs in ET1 and both transistors Q3 and Q5 are turned on and point X goes low, transistor Q6 is turned on and heater HE is energized to generate heat. The IG generates heat instantaneously, and the heat of the explosive IG blows the fuse FU, so that the power supply to the lamp L is stopped.

As described above, according to the fourth embodiment, the fuse FU is connected between the positive terminal of the battery B and the drain of the FET 1, one end of the heater HE is connected to the positive terminal of the battery B, and the other end is connected. Is grounded via the transistor Q6, so that when a short-circuit fault occurs in the FET1, the signal level at the other end of the resistor R9 becomes low, thereby blowing the fuse FU and causing the lamp L due to the short-circuit fault in the FET1. It is possible to reliably stop the continuation of the power supply to the device with a simple configuration.

The fuse FU may be blown directly by the heat of the heater HE without the explosive IG. However, by providing a small amount of explosive IG, the element portion of the fuse FU can be quickly and reliably blown. can do.

FIG. 5 is a circuit diagram of a fifth embodiment of a lamp control circuit to which the short-circuit failure detection circuit according to the present invention is applied. In the fifth embodiment, instead of the electromagnetic relay RL of the first embodiment, a heater HE2 and a positive characteristic (PTC) are used.
mperature Coefficient)) is provided.

In the fifth embodiment, the positive terminal of the battery B is connected to the drain of the FET 1 via the positive characteristic thermistor T1, and the line connecting the positive terminal of the battery B and the positive characteristic thermistor T1 is connected to the heater HE2. one end,
The power supply circuit 2 and the switch drive circuit 3 are connected, and the other end of the heater HE2 is connected to a transistor Q6 via a resistor R10.
Connected to the emitter.

The operation of the fifth embodiment will be described. Under normal conditions, the ambient temperature of the PTC thermistor T1 is -40.
C. to 120.degree. C., and the resistance value of the positive temperature coefficient thermistor T1 at that time is 0.05 .OMEGA. To 0.1 .OMEGA., So that the power supply to the lamp L is not hindered by the positive temperature coefficient thermistor T1.

On the other hand, when a short-circuit fault occurs in the FET 1 and both the transistors Q3 and Q5 are turned on and the point X goes low, the transistor Q6 is turned on and the heater H
E2 is energized to generate heat, and the heat of the heater HE2 raises the temperature of the positive temperature coefficient thermistor T1 to about 140 ° C. to 160 ° C., thereby increasing the resistance value of the positive temperature coefficient thermistor T1 to 10 kΩ to 10 ° C.
The current rises to 0 kΩ, and the current to the lamp L is almost cut off.

As described above, according to the fifth embodiment, the positive temperature coefficient thermistor T1 is connected between the positive terminal of the battery B and the drain of the FET1, and one end of the heater HE2 is connected to the positive terminal of the battery B. The other end is transistor Q6
When the short-circuit fault occurs in the FET1, the signal level at the other end of the resistor R9 becomes low level, thereby increasing the resistance value of the positive temperature coefficient thermistor T1. Lamp L by
It is possible to stop the continuation of power supply to the power supply with a simple configuration.

[0059]

As described above, according to the present invention,
A failure detection signal is output when both the first switch that turns on when no control signal is input to the control terminal and the second switch that turns on when the potential of the second terminal rises are both on. Therefore, when a short-circuit fault occurs in the semiconductor switching element, a fault detection signal can be output, whereby a short-circuit fault of the semiconductor switching element can be reliably detected with a simple configuration.

Further, one end of the resistance element is connected to the high-level signal output means, and the other end of the resistance element is grounded via a series circuit comprising the first switch means and the second switch means. Output a failure detection signal from the other end, a high-level signal is output from the other end of the resistance element in normal times, and a low-level failure detection signal is output when the semiconductor switching element has a short-circuit failure. Thus, a short-circuit failure of the semiconductor switching element can be detected.

A circuit element which can be switched between an energized state and an energized state is connected between the power supply and the first terminal. When a failure detection signal is output from the failure detection signal output section, the circuit element is energized. By controlling to the limit state, when a short circuit fault occurs in the semiconductor switching element, the current flowing from the power supply to the load can be reduced, thereby protecting the load.

A normally closed contact of the electromagnetic relay forms a circuit element, one end of an exciting coil of the electromagnetic relay is connected to a power supply, and the other end of the exciting coil outputs a failure detection signal from a failure detection signal output unit. When the short circuit fault occurs in the semiconductor switching element, the third switch is turned on, and the exciting current flows through the exciting coil to open the normally closed contact. Therefore, the power supply from the power supply to the load can be stopped, whereby the load can be reliably protected.

Further, the circuit element is a positive temperature coefficient thermistor,
One end of the heater disposed close to the positive temperature coefficient thermistor is connected to a power supply, and the other end of the heater is grounded via third switch means which is turned on when a failure detection signal is output from a failure detection signal output unit. As a result, when a short-circuit fault occurs in the semiconductor switching element, the third switch means is turned on, whereby a current flows through the heater to generate heat, and the heat of the heater increases the resistance value of the positive temperature coefficient thermistor. Current flowing from the load to the load can be reduced, thereby protecting the load.

Further, between the high-level signal output means and the ground, the power supply is activated when the power is supplied, and is turned on when the signal level at the other end of the resistance element becomes low. By connecting the series circuit including the switch means, when a short circuit fault occurs in the semiconductor switching element, the notifying means operates to notify a user or the like of the short-circuit fault.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment of a lamp control circuit to which a short-circuit failure detection circuit according to the present invention is applied.

FIG. 2 is a circuit diagram of a second embodiment of the lamp control circuit to which the short-circuit failure detection circuit according to the present invention is applied.

FIG. 3 is a circuit diagram of a third embodiment of a lamp control circuit to which a short-circuit failure detection circuit according to the present invention is applied.

FIG. 4 is a circuit diagram of a fourth embodiment of the lamp control circuit to which the short-circuit failure detection circuit according to the present invention is applied.

FIG. 5 is a circuit diagram of a fifth embodiment of a lamp control circuit to which a short-circuit failure detection circuit according to the present invention is applied.

[Explanation of symbols]

 Reference Signs List 1 FET 2 power supply circuit 3 switch drive circuit 4 switch control section RL electromagnetic relay SW lamp switch R1 to R10 resistor C1 capacitor FU fuse HE, HE2 heater IG gunpowder LED light emitting diode T1 positive temperature coefficient thermistor Q1 to Q6 transistor ZD zener diode

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H03K 17/08 H03K 17/08 C (72) Inventor Takashi Hoshino 1-7-10 Kikuzumi, Minami-ku, Nagoya-shi, Aichi Harness Co., Ltd. Within the Research Institute of Technology

Claims (6)

[Claims] 1. A control terminal, a first terminal connected to a power supply, and a second terminal grounded via a load, wherein the first terminal and the second terminal are controlled by a control signal input to the control terminal. A power supply circuit including a semiconductor switching element whose connection between the control terminal and the control terminal is turned on when the control signal is not input to the control terminal.
A switch, a second switch which is turned on when a potential of the second terminal rises, and a failure detection signal output unit which outputs a failure detection signal when both the first switch and the second switch are on. And a short-circuit failure detection circuit. 2. The short-circuit fault detection circuit according to claim 1, further comprising a high-level signal output means, and a resistance element, wherein one end of said resistance element is connected to said high-level signal output means, An end is grounded via a series circuit including the first switch means and the second switch means, and the failure detection signal output section is configured to output the failure detection signal from the other end of the resistance element. A short-circuit fault detection circuit characterized by being performed. 3. The short-circuit fault detection circuit according to claim 1, wherein the short-circuit fault detection circuit is connected between the power supply and the first terminal.
A circuit element that can be switched between an energized state that permits energization and an energized state that restricts energization, and the circuit element is controlled to the energized state when the failure detection signal is output from the failure detection signal output unit. A short-circuit fault detection circuit, comprising: 4. The short-circuit fault detection circuit according to claim 3, further comprising an electromagnetic relay having a normally closed contact and an exciting coil, wherein the normally closed contact forms the circuit element, and the circuit element control circuit includes the fault. A third switch unit that is turned on when the failure detection signal is output from the detection signal output unit, one end of the excitation coil is connected to the power supply, and the other end of the excitation coil is connected via the third switch unit; A short-circuit fault detection circuit characterized by being configured to be grounded. 5. The short-circuit fault detection circuit according to claim 3, wherein said circuit element is a positive temperature coefficient thermistor, and said resistance control circuit is provided with a heater disposed close to said positive temperature coefficient thermistor, and said fault detection circuit. A third switch unit that is turned on when the failure detection signal is output from the signal output unit, one end of the heater is connected to the power supply, and the other end of the heater is grounded via the third switch unit. A short-circuit fault detection circuit characterized by being configured. 6. The short-circuit fault detecting circuit according to claim 1, wherein the notifying means which operates when energized and notifies the driver, and the signal level at the other end of the resistance element is low. And a fourth circuit, which is turned on when the power is turned on, wherein a series circuit comprising the notification means and the fourth switch is connected between the high-level signal output means and the ground. Failure detection circuit.