JP5286835B2 - Motor control circuit and motor lock abnormality detection method - Google Patents

Description

  The present invention relates to a motor control circuit for controlling a driving switching element connected in series with a motor between a power source and a ground, and a method for detecting a lock abnormality in the motor.

  FIG. 9 shows an example of a conventional configuration of a control device having a function of driving and controlling a DC motor mounted on a vehicle and detecting a lock state of the motor. The motor control circuit 1 drives the DC motor 3 by, for example, PWM (Pulse Width Modulation) control according to a drive command signal given from an engine ECU (Electronic Control Unit) 2. When the drive command signal is converted into a voltage command value in the input signal processing circuit 4, the drive command signal is output to the PWM signal generation circuit 5, and the PWM signal generation circuit 5 converts the applied voltage command value into a voltage of a carrier wave that is, for example, a triangular wave. And generate and output a PWM signal.

  The PWM signal is given to the gate of the N-channel MOSFET 7 through the drive circuit 6. The source of the FET 7 is connected to the ground, and the drain is connected to the negative terminal (M−) of the motor 3. The positive terminal (M +) of the motor 3 is connected to the positive terminal of the battery 8 of the vehicle, and the motor 3 is driven on the low side by the FET 7.

  The positive terminal of the motor 3 is connected to the drain of the FET 7 via a π-type filter 12 including a coil 9 and capacitors 10 and 11 and a free wheel diode 13 in the reverse direction. The drain of the FET 7 is connected to the non-inverting input terminal of the comparator 14, and the determination voltage Vr is applied to the inverting input terminal of the comparator 14. The output signal of the comparator 14 is given to the lock determination circuit 17 via the mask circuit 15 and the monitoring timer 16.

  FIG. 10 is a timing chart showing the operation content of the above configuration. The comparator 14 compares the drain voltage of the FET 7 with the determination voltage Vr to determine whether or not a potential increase indicating that the motor 3 is in the locked state has occurred. Based on the PWM signal supplied from the drive circuit 6, the mask circuit 15 outputs the determination result output from the comparator 14 to the monitoring timer 16 while the FET 7 is ON (for example, the logical product of both signals is obtained). ). The drain voltage during the period when the FET 7 is ON is the product of the ON resistance of the FET 7 and the energization current.

  The monitoring timer 16 counts the number of times the output signal of the mask circuit 15 changes to a high level, and outputs a count-up signal to the lock determination circuit 17 when the count number reaches a predetermined value. That is, if the output signal of the comparator 14 in the ON period of the FET 7 is at a low level, the output signal of the mask circuit 15 is maintained at a low level, and if the output signal of the comparator 14 is high during the same period, the mask circuit 15 The output signal changes to show a high level during the synchronization.

  When the count determination signal is given from the monitoring timer 16, the lock determination circuit 17 gives a drive stop signal to the drive circuit 6 to stop the output of the PWM signal. Then, since the magnetic energy accumulated in the coil of the motor 3 at that time flows as a delay current through the diode 13, the drain voltage is obtained by adding the forward voltage Vf of the diode 13 to the voltage + B of the battery 8. It will be a thing. When all the magnetic energy is consumed, the drain voltage becomes equal to + B.

The temperature protection circuit 18 detects the temperature of the FET 7 with a thermistor or the like, and when it detects that the temperature has risen excessively, it also gives a drive stop signal to the drive circuit 6 to stop the output of the PWM signal. In the above, the motor control circuit 1 plus the FET 7, the filter 12, and the diode 13 constitutes the motor driving device 19. A configuration similar to that shown in FIG. 9 is disclosed in Patent Document 1, for example.
JP 2008-11671 A

  In the above configuration, the drain voltage when the FET 7 is turned on depends on the ON resistance of the FET 7. However, the ON resistance of the FET varies greatly between individual elements, and varies greatly depending on the temperature and the gate voltage. Therefore, the detection accuracy of the lock state in the above configuration is lowered. Therefore, in order to avoid making an erroneous determination when the motor 3 is rotating normally, it is necessary to set a high determination voltage Vr to which the comparator 14 refers to take a margin. Then, on the other hand, if the motor 3 is locked while the voltage + B of the battery 8 is reduced, the locked state may not be detected.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a motor control circuit and a motor lock abnormality detection method capable of more reliably detecting motor lock abnormality.

According to the motor control circuit of claim 1, when the current flowing during the period when the drive switching element is ON is detected as a voltage, and the comparison result by the voltage comparison means indicates that the motor is in a locked state, The drive stop means stops the control of the drive switching element. Thereafter, it is determined whether or not the motor is idling by the idling determination means, and the lock abnormality detecting means detects the motor lock abnormality when the idling of the motor is not determined.
In other words, if the motor is not actually in a locked state, the motor continues to idle for a while due to inertia even if the control of the driving switching element is stopped. Therefore, if it is confirmed that the motor is not idling after the control of the driving switching element is stopped, the lock abnormality can be reliably detected even when the power supply voltage fluctuates.
The determination voltage changing unit changes the determination voltage of the voltage comparison unit when the idling determination unit determines that the motor is idling. That is, since the case indicates that the comparison result by the voltage comparison means is an erroneous determination, it is possible to avoid subsequent erroneous determination by changing the determination voltage.

According to the motor control circuit of the second aspect, the idling determination means determines idling of the motor depending on whether or not the generated voltage by the motor is detected. That is, since the motor acts as a generator if the motor is idling, idling can be reliably determined based on whether or not the generated voltage is detected.
Specifically, the idling determination means determines idling of the motor by comparing a voltage at a common connection point between the driving switching element and the motor with a determination voltage. That is, when the motor is idling and generating electric power, the voltage appears at the common connection point, so that idling can be easily determined.
The voltage comparison unit and the idling determination unit are configured by a common comparator, and the determination voltage switching unit switches the determination voltage corresponding to each function and outputs it to the comparator. Therefore, circuit components can be shared and configured at low cost.
According to the motor control circuit of the fourth aspect, the idling determination means determines idling of the motor based on whether or not the voltage at the common connection point between the driving switching element and the motor indicates a pulsating state. In other words, depending on the type of motor being used and the rotation conditions, a pulsating voltage is generated when the electrical connection between the motor brush and the commutator is switched, which affects the generated voltage when the motor is idling. May have an effect. Therefore, idling can be determined based on whether or not the pulsating voltage is generated.

According to the motor control circuit of the fifth aspect , the idling determination means determines idling of the motor when a predetermined waiting time elapses after the control of the driving switching element is stopped by the driving stop means. That is, immediately after the energization of the motor coil is stopped, the magnetic energy accumulated in the coil at that time flows as a delayed current, and therefore it is difficult to determine idling of the motor. Therefore, if the determination is made after the standby time has elapsed, the determination can be made accurately with the delayed current disappearing.

According to the motor control circuit of the sixth aspect, when the state indicating the motor lock based on the comparison result by the voltage comparison means has passed a predetermined monitoring time, the drive stop means stops the control of the drive switching element. That is, since it is also assumed that noise is applied to the detection voltage of the voltage comparison means, it is possible to achieve more accuracy by stopping the control of the driving switching element after the monitoring time has elapsed.

According to the motor control circuit of the seventh aspect , the voltage detecting means includes a resistance element that is energized via the driving switching element. That is, by using the detection resistance element, it is possible to detect the current flowing during the period when the driving switching element is ON as a stable voltage value.

(First embodiment)
A first embodiment of the present invention will be described below with reference to FIGS. The same parts as those in FIG. 9 are denoted by the same reference numerals, description thereof is omitted, and different parts are described below. As shown in FIG. 1, the motor control circuit 21 of this embodiment includes a comparator 22, a mask circuit 23, a monitoring timer 24, a lock determination release command circuit 25, a mask time setting circuit 26, and a lock determination value setting. The circuit 27 (determination voltage changing means) is provided. Further, the lock determination circuit 17 is replaced with a lock determination circuit 28.

The inverting input terminal of the comparator 22 is connected to the drain of the FET 7, and the determination voltage Vg is applied to the non-inverting input terminal. A mask circuit 23 and a monitoring timer 24 are connected in series to the output terminal of the comparator 22 in the same manner as the mask circuit 15 and the monitoring timer 16.
The comparator 22 is used to monitor the drain voltage of the FET 7 to determine whether the motor 3 is idling after the driving of the motor 3 by the FET 7 is stopped. Therefore, the determination voltage Vg is set to a level slightly lower than the power supply voltage + B in order to perform the above determination.

  The output terminal of the monitoring timer 24 is connected to the lock determination release instruction circuit 25, and the lock determination release instruction circuit 25 outputs a control signal to the lock determination circuit 28 and the lock determination value setting circuit 27. The output signal of the input signal processing circuit 4 is also given to the mask time setting circuit 26, and the mask time setting circuit 26 variably sets the time for masking the output signal of the comparator 22 by the mask circuit 23.

  In the above configuration, the mask circuit 23, the monitoring timer 24, the lock determination release command circuit 25, and the mask time setting circuit 26 constitute the idling determination means 29. The motor drive device 30 is configured by replacing the control circuit 1 in the drive device 19 of FIG. In FIG. 1 and FIG. 2, in order to simplify the description, the comparator 14, the mask circuit 15, and the monitoring timer 16 are marked with “1”, and the comparator 22, mask circuit 23, and monitoring timer 24 are circled. “2” is attached.

  Next, the operation of the present embodiment will be described with reference to FIG. The lock determination by the comparator 14 (voltage comparison means), the mask circuit 15 and the monitoring timer 16 is basically performed in the same manner as the control circuit 1, but the lock determination circuit 28 (lock abnormality detection means, drive stop means) is monitored. When the count-up signal is given from the timer 16, a drive stop signal is given to the drive circuit 6 and the mask circuit 23 is activated. Incidentally, the mask circuit 23 naturally continues to prevent signal output in a state before being activated, and when activated, the mask circuit 23 measures a predetermined time for masking the signal output from that point.

  As described above, while the delayed current flows through the diode 13, the mask circuit 23 continues to maintain the mask state. The finite mask time here is preferably set according to the period during which the lag current flows. Therefore, in this embodiment, the mask time setting circuit 26 variably sets the mask time according to the level of the PWM command signal generated in the input signal processing circuit 4. That is, the time for which the delay current flows is determined by the magnitude of the magnetic energy accumulated in the coil of the motor 3.

  When the measurement of the mask time in the mask circuit 23 is completed, the output signal of the comparator 23 is given to the monitoring timer 24. FIG. 2 shows a case where the lock determination by the comparator 14 is an erroneous determination and the motor 3 is idling due to inertia after the driving by the FET 7 is stopped. At this time, since the voltage generated by the motor 3 has a reverse polarity with respect to the battery voltage + B, the drain voltage of the FET 7 is significantly lower than + B and increases with a decrease in the generated voltage. Therefore, the comparator 22 continues to output a high level signal while the drain voltage is lower than the determination voltage Vg in the above state.

The monitoring timer 24 measures a period during which the signal supplied through the mask circuit 23 is at a high level, and outputs an erroneous determination detection signal to the lock determination release command circuit 25 when it reaches a predetermined time. The lock determination release instruction circuit 25 receives the signal and gives a lock determination release instruction to the lock determination circuit 28 and the lock determination threshold setting circuit 27. Then, the lock determination circuit 28 stops the output of the drive stop signal and causes the drive circuit 6 to restart the output of the PWM signal. Further, the lock determination threshold value setting circuit 27 changes the lock determination threshold voltage applied to the comparator 14 to be slightly higher in order to avoid subsequent erroneous determination.
When the comparison result of the comparator 14 is not an erroneous determination and the motor 3 is actually locked, the change in the drain voltage after the masking by the mask circuit 23 is released is the same as in FIG. .

  As described above, according to the present embodiment, the motor control circuit 21 detects the current flowing during the period when the FET 7 is ON based on the drain voltage, and the comparison result by the comparator 14 indicates that the motor 3 is in the locked state. As shown, the lock determination circuit 28 stops the control of the FET 7. Thereafter, whether or not the motor 3 is idling is determined by the idling determination means 29, and the lock determination circuit 28 detects a lock abnormality when the idling of the motor 3 is not determined. Therefore, even if the determination result of the comparator 14 is incorrect due to fluctuations in the power supply voltage + B, it is possible to reliably detect the lock abnormality of the motor 3. Since the lock determination threshold value setting circuit 27 changes the determination voltage of the comparator 14 when the idling determination means 29 determines that the idling of the motor is determined, it is possible to avoid subsequent erroneous determination.

Further, the idling determination means 29 determines idling of the motor 3 when a predetermined waiting time by the mask circuit 23 has elapsed after the control of the FET 7 is stopped, so that the idling determination means 29 determines according to the magnetic energy accumulated in the coil of the motor 3. Accurate determination can be made at the stage where the flowing delay current disappears.
Furthermore, the lock determination circuit 28 stops the control of the FET 7 when the state indicating the lock based on the comparison result by the comparator 14 has passed a predetermined monitoring time, so that it is possible to eliminate the influence of noise and the like to achieve more accuracy. it can. Since the idling determination means 29 determines idling of the motor 3 based on whether or not the generated voltage by the motor 3 is detected, it can reliably determine idling. Further, the idling determination means 29 can easily determine idling of the motor 3 by comparing the drain voltage of the FET 7 with the determination voltage Vg.

(Second embodiment)
FIG. 3 shows a second embodiment of the present invention. The same parts as those of the first embodiment are denoted by the same reference numerals, the description thereof is omitted, and different parts will be described below. In the motor control circuit 31 of the second embodiment, a resistance element 32 (voltage detection means) for current detection is inserted between the source of the FET 7 and the ground, and the inverting input terminal of the comparator 14 is connected to the drain of the FET 7. Instead, it is connected to a common connection point between the source and the resistance element 32. Other configurations are the same as those of the first embodiment.
According to the second embodiment configured as described above, the current flowing through the FET 7 can be detected as a stable voltage value by using the resistance element 32 for current detection.

As described above, according to the third embodiment, the voltage comparison unit and the idling determination unit are configured by the common comparator 14, and the determination voltage switching unit 39 switches the determination voltage corresponding to each function and outputs it to the comparator 14. Therefore, circuit components can be shared and configured at low cost.

  Next, the operation of the third embodiment will be described. During a period in which the comparator 14 refers to the drain voltage of the FET 7 as a voltage comparison means, the lock determination circuit 27 does not output a drive stop signal, and the lock determination value switching circuit 38 keeps the FET 35 OFF. At this time, the determination voltage given to the comparator 14 is at the same level as the determination voltage Vr in the first embodiment.

  When the lock state is determined based on the comparison result of the comparator 14 and the lock determination circuit 27 outputs a drive stop signal, the lock determination value switching circuit 38 turns on the FET 35. At this time, if the forward voltage of the diodes 36 and 37 is Vf and the voltage drop due to the ON resistance of the FET 35 is ignored, the determination voltage Vr given to the comparator 14 becomes (+ B−2Vf). As a means, the drain voltage of the FET 7 is referred to.

  As described above, according to the third embodiment, the voltage determination unit and the idling determination unit are configured by the common comparator 14, and the determination voltage switching unit 39 switches the determination voltage corresponding to each function and outputs it to the comparator 14. Therefore, circuit components can be shared and configured at low cost.

(Fourth embodiment)
5 and 6 show a fourth embodiment of the present invention. In the motor control circuit 41 of the fourth embodiment, the drain of the FET 7 is connected to the input terminal of the mask circuit 23 instead of the comparator 22, and the output terminal of the monitoring timer 24 is the input terminal of the pulsating current detection circuit 42. It is connected to the. The output terminal of the pulsating flow detection circuit 42 is connected to the non-inverting input terminal of the comparator 22, and the determination voltage Vp is applied to the inverting input terminal of the comparator 22. The output terminal of the comparator 22 is connected to the input terminal of the lock determination release command circuit 25. In the above configuration, the one provided with the pulsating flow detection circuit 42 on the comparator 22 side constitutes the idling determination means 43.

  Next, the operation of the fourth embodiment will be described with reference to FIG. In the fourth embodiment, if the comparison result of the comparator 14 is erroneously determined and the driving of the motor 3 by the FET 7 is stopped, whether or not the motor 3 is idling and whether or not the pulsating voltage is detected. To do. In other words, in the case of the DC motor 3, depending on the rotation conditions, a pulsating voltage is generated when the electrical connection state of the brush of the motor 3 and the commutator is switched, which may affect the generated voltage when idling. Therefore, the generation of the pulsating voltage is detected (see FIG. 6).

The pulsating current detection circuit 42 samples the drain voltage of the FET 7 given via the monitoring timer 24 at a predetermined period, and detects the maximum value and the minimum value of the voltage within the sampling period. Then, the difference between the two is measured, and the measurement result is output to the comparator 22 as an analog voltage. The comparator 22 compares the voltage of the measurement result with the determination voltage Vp, and when detecting the occurrence of the pulsating flow, sets the output signal to a high level. The subsequent operation is the same as that of the first embodiment.
Also in the case of the fourth embodiment configured as described above, the idling of the motor 3 can be determined.

(5th Example)
FIG. 7 shows a fifth embodiment of the present invention, and different portions from the first embodiment will be described. In the fifth embodiment, the present invention is applied to the case where the P-channel MOSFET 51 is used as the driving switching element and the motor 3 is driven on the high side. In this case, the drain of the FET 51 is connected to the filter 12 side, and the source side is connected to the motor 3 and the cathode of the diode 13 in the reverse direction.

The source and drain of the FET 51 are connected to the input terminal of a differential amplifier 53 mainly composed of an operational amplifier 52. The non-inverting input terminal of the comparator 14 and the inverting input terminal of the comparator 22 are connected to the differential terminal. The output terminal of the amplifier 53 is connected. Therefore, the motor control circuit 54 is configured by adding the differential amplifier 53 to the motor control circuit 21 of the first embodiment.
According to the motor control circuit 54 configured as described above, the operation content is exactly the same as that of the first embodiment, and the operation timing chart is the same as FIG. Therefore, the present invention can also be applied to the high side drive system.

(Sixth embodiment)
FIG. 8 shows a sixth embodiment of the present invention, and different parts from the first embodiment will be described. In the sixth embodiment, the present invention is applied to a control circuit 55 that linearly controls the motor 3. In this case, the PMW signal generation circuit 5 and the filter 12 are not necessary. The present invention can be similarly applied to such a configuration.

The present invention is not limited to the embodiments described above and shown in the drawings, and the following modifications or expansions are possible.
The initial value of the determination voltage Vr applied to the comparator 14 may be set so as to increase linearly in accordance with the PWM control command generated by the input signal processing circuit 4.
When the determination result by the comparator 14 detects the locked state of the motor 3, the drive control may be stopped immediately.
The process of changing the determination voltage when the determination by the comparator 14 is incorrect may be performed as necessary.

The temperature protection circuit 18 may be disposed as necessary. Further, the lock determination value setting circuit 27 may be provided as necessary.
When the idling of the motor 3 is determined, the determination may be performed immediately after the drive control is stopped.
A bipolar transistor or IGBT may be used as the driving switching element.
The present invention is not limited to drive control of a DC motor mounted on a vehicle, and can be widely applied as long as it is configured to drive control a DC motor.

1 is a functional block diagram illustrating a configuration of a motor control circuit according to a first embodiment of the present invention. Operation timing chart FIG. 1 equivalent view showing a second embodiment of the present invention. FIG. 1 equivalent view showing a third embodiment of the present invention. FIG. 1 equivalent view showing a fourth embodiment of the present invention. 2 equivalent diagram FIG. 1 equivalent view showing a fifth embodiment of the present invention. FIG. 1 equivalent view showing a sixth embodiment of the present invention. 1 equivalent diagram showing the prior art 2 equivalent diagram

Explanation of symbols

  In the drawing, 3 is a DC motor, 7 is an N-channel MOSFET (driving switching element, voltage detection means), 14 is a comparator (voltage comparison means), 21 is a motor control circuit, 27 is a lock determination value setting circuit (determination voltage change) Means), 28 is a lock determination circuit (lock abnormality detection means, drive stop means), 29 is an idling determination means, 31 is a motor control circuit, 32 is a resistance element (voltage detection means), 33 is a motor control circuit, and 39 is a determination. Voltage switching means, 41 is a motor control circuit, 43 is idling determination means, 51 is a P-channel MOSFET (driving switching element, voltage detection means), and 54 and 55 are motor control circuits.

Claims (14)

In the motor control circuit that controls the driving switching element connected in series with the motor between the power source and the ground,
Voltage detection means for detecting, as a voltage, a current flowing during a period when the driving switching element is ON;
Voltage comparison means for comparing the voltage detected by the voltage detection means with a determination voltage;
When the comparison result by the voltage comparison means indicates that the motor is in a locked state, drive stop means for stopping control of the drive switching element; and
An idling judging means for judging whether or not the motor is idling after the control of the driving switching element is stopped;
A lock abnormality detecting means for detecting a lock abnormality of the motor when the idling determination means does not determine the idling of the motor ;
A motor control circuit comprising: determination voltage changing means for changing the determination voltage of the voltage comparison means when the idling determination means determines that the motor is idling . In the motor control circuit that controls the driving switching element connected in series with the motor between the power source and the ground,
Voltage detection means for detecting, as a voltage, a current flowing during a period when the driving switching element is ON;
Voltage comparison means for comparing the voltage detected by the voltage detection means with a determination voltage;
When the comparison result by the voltage comparison means indicates that the motor is in a locked state, drive stop means for stopping control of the drive switching element; and
An idling judging means for judging whether or not the motor is idling after the control of the driving switching element is stopped;
A lock abnormality detection means for detecting a lock abnormality of the motor when the idling determination means does not determine the idling of the motor;
The idling determination means determines idling of the motor according to whether or not a generated voltage by the motor is detected by comparing a voltage at a common connection point between the driving switching element and the motor with a determination voltage. ,
The voltage comparison means and the idling determination means are configured with a common comparator,
A motor control circuit comprising: a judgment voltage switching means for switching and outputting a judgment voltage when functioning as the voltage comparison means and a judgment voltage when functioning as the idling judgment means. 3. The motor control circuit according to claim 2 , further comprising determination voltage changing means for changing a determination voltage of the voltage comparison means when the idling determination means determines that the motor is idling . The idling determination means determines idling of the motor according to whether or not a voltage at a common connection point between the driving switching element and the motor indicates a pulsating state. Motor control circuit. 5. The idling determination unit determines idling of the motor when a predetermined standby time has elapsed after the control of the driving switching element is stopped by the driving stop unit. A motor control circuit according to claim 1. The drive stop unit stops the control of the drive switching element when a comparison result by the voltage comparison unit indicates that the motor is in a locked state after a predetermined monitoring time has elapsed. The motor control circuit according to claim 1 . The motor control circuit according to claim 1, wherein the voltage detection unit includes a resistance element that is energized via the driving switching element . It is applied when controlling the drive switching element connected in series with the motor between the power supply and the ground.
A current flowing during a period in which the driving switching element is ON is detected as a voltage;
If the result of comparing the detected voltage with the determination voltage indicates that the motor is in a locked state, the control of the driving switching element is stopped,
After stopping the control of the switching element for driving, it is determined whether or not the motor is idling, and when the idling of the motor is not determined, the motor lock abnormality is detected, and the idling of the motor is detected. A motor lock abnormality detection method, wherein the determination voltage is changed when it is determined . It is applied when controlling the drive switching element connected in series with the motor between the power supply and the ground.
A current flowing during a period in which the driving switching element is ON is detected as a voltage;
If the result of comparing the detected voltage with the determination voltage indicates that the motor is in a locked state, the control of the driving switching element is stopped,
After stopping the control of the switching element for driving, it is determined whether or not the motor is idling, and when the idling of the motor is not determined, the lock abnormality of the motor is detected,
By comparing the voltage at the common connection point between the drive switching element and the motor with a determination voltage, whether or not the generated voltage by the motor is detected, it is determined whether the motor is idling,
The means for comparing the voltage at the common connection point with the determination voltage and the means for determining the idling are constituted by a common comparator, and the comparator has a determination voltage when compared with the voltage at the common connection point , A method for detecting abnormality in a motor lock, wherein the determination voltage for determining idling is switched and output. The motor lock abnormality detection method according to claim 9, wherein when the idling of the motor is determined, the determination voltage is changed . The motor lock abnormality detection according to claim 9 or 10 , wherein the idling of the motor is determined based on whether or not a voltage at a common connection point between the driving switching element and the motor indicates a pulsating state. Method. The motor lock abnormality detection method according to any one of claims 8 to 11 , wherein when the predetermined standby time has elapsed after the control of the drive switching element is stopped, the idling of the motor is determined. Comparison result of the voltage, the state indicating that the motor is in a locked state has passed a predetermined monitoring time, any one of claims 8 to 12, characterized in that stops control of the driving switching element The motor lock abnormality detection method described in 1. 14. The motor lock abnormality detection method according to claim 8, wherein the detected voltage is compared with the determination voltage by a resistance element energized through the driving switching element.

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