JP2008178200A - Power semiconductor switching circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power semiconductor switching circuit wherein heating from a power semiconductor switching element and switching surge are reduced in a balanced manner. <P>SOLUTION: The temperature of the power semiconductor switching element is detected (S102). When the temperature rises (S104), a supply voltage applied to a drive circuit for driving the power semiconductor switching element is increased (S110) to reduce resistance loss in the power semiconductor switching element. When the temperature falls, the supply voltage applied to the drive circuit for driving the power semiconductor switching element is reduced (S106) to reduce the switching surge voltage of the power semiconductor switching element. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power semiconductor switching circuit, and more particularly to realization of a suitable intermittent operation of the power semiconductor switching element.

For example, a three-phase inverter circuit containing a total of six power semiconductor switching elements is used to drive an in-vehicle three-phase AC motor. A power MOS transistor, IGBT, or the like is used as the power semiconductor switching element. In order to drive these power semiconductor switching elements, a drive circuit is used that amplifies an input pulse signal voltage for switching control of the power semiconductor switching elements input from the outside and applies them to the control electrodes of the power semiconductor switching elements. . As the drive circuit, for example, a complementary CMOS inverter is used. The main electrode terminal of the power semiconductor switching element is supplied with a power supply voltage Vcc from a battery or the like. For example, this type of power semiconductor switching circuit is described in Patent Document 1 below.
JP 2004-222420 A

  Various power conditions are required for the power semiconductor switching element described above. One absolute operating condition is that the chip temperature does not exceed an acceptable range. Another operating condition that has been emphasized in recent years is that the switching surge voltage does not exceed the allowable range. There are various other operating conditions.

  An object of the present invention is to provide a power semiconductor switching circuit capable of satisfying a plurality of operating conditions required for a power semiconductor switching element in a balanced manner.

  The present invention for solving the above problems includes a power semiconductor switching element that switches a load current, and a drive circuit that applies a control voltage formed by at least amplifying an input pulse signal voltage to a control electrode of the power semiconductor switching element. A power semiconductor switching circuit comprising: a power supply voltage stabilization circuit that creates a stabilized power supply voltage and applies the stabilized power supply voltage to the drive circuit; a temperature detection circuit that detects a temperature signal correlated with the temperature of the power semiconductor switching element; A control circuit that changes the stabilized power supply voltage based on the detected temperature signal, and the control circuit instructs the power supply voltage stabilization circuit when the temperature becomes high, and the stabilized power supply. Before the drive circuit outputs to the power semiconductor switching element by increasing the voltage The drive circuit outputs to the power semiconductor switching element by increasing the high level of the control voltage and instructing the power supply voltage stabilization circuit to decrease the stabilized power supply voltage when the temperature becomes low It is characterized by lowering the high level of the control voltage.

  That is, according to the present invention, the power supply voltage applied to the drive circuit is increased when it is determined that the power semiconductor switching element has reached a high temperature. As a result, the on-resistance of the power semiconductor switching element is lowered, the resistance loss (heat generation amount) is reduced, and the temperature rise of the power semiconductor switching element can be suppressed or lowered.

  Conversely, when it is determined that the power semiconductor switching element has become low temperature, the power supply voltage applied to the drive circuit is reduced. Thereby, it is possible to reduce the switching surge voltage generated particularly when the power semiconductor switching element is turned on. More specifically, for example, in a full bridge circuit, the other power semiconductor switching element is turned off during an on-transition period of one power semiconductor switching element. At this time, voltage oscillation due to resonance between the parasitic capacitance of the power semiconductor switching element to be turned off and the wiring inductance is generated as a switching surge voltage. According to the present invention, when the temperature of the power semiconductor switching element is low, the power supply voltage applied to the drive circuit is reduced, so that the on-resistance of the power semiconductor switching element is increased and the on-transition period is extended. The voltage change rate of the main electrode terminal of the switching element is relaxed, and the switching surge voltage is reduced. In addition, a decrease in the control voltage applied to the control electrode of the power semiconductor switching element can extend the life of the power semiconductor switching element.

  In a preferred aspect, the power supply voltage stabilization circuit includes a voltage regulator that intermittently controls the power supply voltage applied to the drive circuit based on a comparison result between the divided output voltage and a predetermined threshold voltage, The control circuit changes at least one of the divided voltage of the output voltage and the threshold voltage based on the temperature signal. In this way, the power supply voltage applied to the drive circuit can be changed with a simple circuit configuration, and voltage fluctuations of the power supply voltage can be reduced. In other words, it is possible to achieve a reduction in adverse effects caused by fluctuations in the power supply voltage of the drive circuit and switching of the power supply voltage of the drive circuit depending on the temperature of the power semiconductor switching element with a substantially common circuit.

  In a preferred embodiment, the power supply voltage stabilization circuit includes a three-phase inverter circuit configured by six power semiconductor switching elements, and the power supply voltage stabilization circuit is configured to drive the power semiconductor switching elements on each phase upper arm side. Three upper arm side voltage regulators that individually supply power supply voltage to the two drive circuits, and three power supply voltages individually supplied to the three drive circuits for driving the power semiconductor switching elements on the lower arm side of each phase One lower arm side voltage regulator. In this way, the control voltage is changed according to the temperature for each power semiconductor switching element of the three-phase inverter circuit while suppressing the complexity of the circuit scale due to the increase in the number of power supply voltage stabilizing circuits. Can do.

  In a preferred embodiment, a total of four voltage regulators are controlled by the temperature signal from a common temperature detection circuit. In this way, the circuit configuration can be simplified.

  In a preferred aspect, the control circuit increases the input power supply voltage of the power supply voltage stabilization circuit when increasing the stabilized power supply voltage and increases the input power supply voltage of the power supply voltage stabilization circuit when decreasing the stabilized power supply voltage. Reduce the input power supply voltage. In this way, the voltage regulator forming the power supply voltage stabilization circuit only needs to receive a relatively low input power supply voltage when the output voltage, that is, the power supply voltage of the drive circuit may be small. Internal loss can be reduced. Conversely, when the output voltage of the voltage regulator, that is, the power supply voltage of the drive circuit needs to be large, a relatively high input power supply voltage is input to the voltage regulator. Therefore, the voltage regulator is within this input power supply voltage range. A necessary high output voltage can be output as the power supply voltage of the drive circuit.

  In a preferred aspect, the control circuit increases an input power supply voltage of the power supply voltage stabilization circuit when the stabilized power supply voltage exceeds a predetermined high level threshold when increasing the stabilized power supply voltage. In the case of increasing and decreasing the stabilized power supply voltage, if the stabilized power supply voltage becomes less than a predetermined low level threshold value lower than the high level threshold value, the input power supply of the power supply voltage stabilization circuit Reduce voltage. In this way, for example, the voltage regulator as the power supply voltage stabilization circuit can output the output voltage of the magnitude required for the drive circuit within the range of the input power supply voltage received by itself to the voltage regulator. In order to increase the input power supply voltage to the power supply voltage stabilization circuit when output of a larger voltage is required without increasing the input power supply voltage, the voltage use efficiency is improved and the loss of the voltage regulator is reduced. be able to.

  As the voltage regulator, it is preferable to employ a so-called series regulator.

  In a preferred aspect, the power semiconductor switching element has a control electrode composed of a gate electrode, and the control circuit substantially increases the output impedance of the drive circuit when the stabilized power supply voltage is increased. When the stabilized power supply voltage is decreased, the output impedance of the drive circuit is substantially decreased. In this way, an increase in the switching surge voltage of the power semiconductor switching element due to an increase in the power supply voltage of the drive circuit due to an increase in the temperature of the power semiconductor switching element can be suppressed. That is, in the on-transition period of the power semiconductor switching element, the final gate voltage becomes a high level, but the increase rate of the gate voltage, that is, the gate voltage change rate is mitigated by the increase in the output impedance of the drive circuit. The above-described resonance voltage component in the on-transition period can be reduced.

  In a preferred aspect, the drive circuit includes a plurality of drive circuits that drive the same power semiconductor switching elements in parallel by operating in parallel, and the control circuit includes a plurality of drive circuits that increase the stabilized power supply voltage. When a part is stopped and the stabilized power supply voltage is decreased, all of the plurality of drive circuits are operated. In this way, the output impedance change of the drive circuit described above can be realized with a simple circuit configuration.

  A three-phase inverter device for driving an in-vehicle motor to which the present invention is applied will be described below with reference to the drawings. However, it goes without saying that the technical idea of the present invention may be realized using other circuits. For example, the following controller 3 with a built-in microcomputer may have a hardware circuit configuration.

(Embodiment 1)
(Circuit configuration)
The three-phase inverter device will be described with reference to the circuit diagram shown in FIG. This three-phase inverter device has a three-phase inverter circuit 1, a temperature sensor 2, and a controller (control circuit) 3 with a built-in microcomputer.

  The three-phase inverter circuit 1 has a total of six IGBTs 4 to 9 that form a three-phase upper arm element and a lower arm element, which constitute a three-phase half-bridge circuit. A circuit composed of these three-phase half-bridge circuits is generally called a three-phase inverter circuit in a narrow sense, but in this embodiment, it is simply called a power circuit section.

  The three-phase inverter circuit 1 includes drive circuits 10 to 15 for individually driving the gate electrodes of the IGBTs 4 to 6 on the upper arm side and the gate electrodes of the IGBTs 7 to 9 on the lower arm side, and power supply voltages to the drive circuits 10 to 12 individually. A voltage regulator (power supply voltage stabilization circuit as referred to in the present invention) 16 to 18 and a voltage regulator (power supply voltage stabilization circuit as referred to in the present invention) 19 to apply a power supply voltage in common to the drive circuits 13 to 15 are provided. Have.

  Since the power circuit section itself forming a so-called three-phase inverter circuit is well known, the description thereof is omitted.

  The drive circuits 10 to 15 form a gate voltage with reference to the emitter electrode potential of the IGBT driven by itself, and apply it to the gate electrode of the IGBT driven by itself. The voltage regulators 16 to 19 form a stabilized power supply voltage based on the emitter potential of the IGBT driven by the drive circuit that supplies power supply power, and apply the stabilized power supply voltage to the drive circuits 10 to 15. Therefore, four types of input power supply voltages having different reference potentials are individually applied to the voltage regulators 16 to 19. In FIG. 1, VHU is an input power supply voltage applied to the voltage regulator 16 on the U-phase upper arm side, VHU-H is its high level potential, and VHU-L is its low level potential. VHV is an input power supply voltage applied to the voltage regulator 17 on the V-phase upper arm side, VHV-H is its high level potential, and VHV-L is its low level potential. VHW is an input power supply voltage applied to the voltage regulator 18 on the W-phase upper arm side, VHW-H is its high level potential, and VHW-L is its low level potential. VL is a high level potential of the input power supply voltage applied to the voltage regulator 19 on the three-phase lower arm side. As shown in FIG. 1, the low level potential of the input power supply voltage is the ground potential.

  An example of an insulated power supply circuit that forms these four input power supply voltages is shown in FIG. Reference numeral 20 denotes a transformer having one primary coil and four secondary coils. The current fed from the battery 21 to the primary coil is PWM feedback controlled by the switch 220. A MOS transistor is preferably employed as the switch 220, and a flywheel diode is connected in reverse parallel to the MOS transistor. Alternatively, the flywheel diode is connected in parallel with the primary coil. The PWM feedback control itself is well known. By comparing any of the output voltages of the four rectifier circuits described later with a predetermined target voltage, and controlling the duty ratio of the switch 220 based on the result, The output voltage (the input power supply voltage of the voltage regulator referred to in the present invention) is converged to the target voltage.

  The four rectifier circuits are constituted by diodes 22 to 25. The secondary voltages output from the four secondary coils are individually half-wave rectified by the four diodes 22 to 25 and then individually smoothed by the capacitors 26 to 29, so that the four types of input power supply voltages VHU described above are obtained. , VHV, VHW, VL are formed.

  In addition to the insulated power supply circuit using the transformer shown in FIG. 2, an insulated power supply circuit using a bootstrap circuit type or a charge pump circuit may be adopted.

  A circuit configuration example of the voltage regulator 16 employed in this embodiment will be described with reference to FIG. Other voltage regulators and drive circuits have the same circuit configuration. Since the voltage regulator 16 employed in this embodiment has a general circuit configuration, it will be briefly described.

  The voltage regulator 16 includes a current control transistor 30 composed of a PNP transistor with a common base, a comparator 31 that switches the current control transistor 30, a resistance voltage dividing circuit 32, and a threshold voltage generation circuit 33.

  The resistance voltage dividing circuit 32 is connected in series with each other and voltage dividing resistors 34 and 35 constituting a resistance voltage dividing circuit for dividing the collector voltage of the current control transistor 30, and is connected in series with each other and in parallel with the voltage dividing resistor 35. An adjustment resistor 36 and a changeover switch 37 are connected. The threshold voltage generation circuit 33 is a constant voltage circuit that outputs a threshold voltage Vref.

  Explaining the operation, if the input power supply voltage VHU of the voltage regulator 16 is increased while the changeover switch 37 is OFF, the divided voltage input to the + input terminal of the comparator 31 becomes higher than the threshold voltage Vref. As a result, the comparator 31 outputs a high level to the current control transistor 30, and the current control transistor 30 is turned off to lower its collector voltage, that is, the power supply voltage of the drive circuit 10, thereby the output voltage of the voltage regulator 16 (drive circuit). 10 power supply voltage).

  On the other hand, when the input power supply voltage of the voltage regulator 16 is lowered, the divided voltage inputted to the + input terminal of the comparator 31 becomes lower than the threshold voltage Vref. As a result, the comparator 31 outputs a low level to the current control transistor 30, and the current control transistor 30 is turned on to increase its collector voltage. As a result, the output voltage of the voltage regulator 16 (power supply voltage of the drive circuit 10) is increased, and the output voltage of the voltage regulator 16 (power supply voltage of the drive circuit 10) is stabilized.

  When the changeover switch 37 is turned on by a command from the controller 3 described later, the adjustment resistor 36 is connected in parallel to the voltage dividing resistor 35. Therefore, the divided voltage input to the comparator 31 is reduced, and the duty ratio of the comparator is increased by that amount. As a result, the average value of the output voltage (U-phase power supply voltage) Vu of the current control transistor 30 increases. That is, the voltage regulator 16 shown in FIG. 3 has a circuit function for switching the output voltage Vu in two stages in addition to a circuit function for stabilizing the output voltage Vu.

  The drive circuit 10 is shown in FIG. In this embodiment, the drive circuit 10 uses complementary CMOS inverters 10a and 10b connected in parallel. Control signals S1 to S4 are applied to a total of four transistors of the complementary CMOS inverters 10a and 10b. The circuit configuration of the drive circuits 11 to 15 is the same as that of the drive circuit 10 described above. Of course, other known circuits may be employed as the drive circuits 10-15.

  In order to switch the power supply voltage of the drive circuit 10, various modifications can be made besides switching the resistance value of the resistance voltage dividing circuit of the voltage regulator 16 by the changeover switch 37. For example, the threshold voltage Vref applied to the negative input terminal of the comparator 31 may be switched. Although the threshold voltage generation circuit 33 is configured using one Zener diode in FIG. 3, various known constant voltage generation circuits can be employed. Alternatively, the digital command value output from the controller 3 may be D / A converted to generate an analog threshold voltage, which is held in a hold circuit and applied to the negative input terminal of the comparator 31. In this way, the output voltage of the voltage regulator 16 (power supply voltage of the drive circuit 10) can be adjusted continuously.

  The temperature sensor 2 employs a thermistor type temperature detection circuit arranged in the vicinity of the IGBT 7. Therefore, the temperature sensor 2 can be regarded as detecting the temperature of the IGBT 7 substantially. Of course, a temperature sensor may be arranged close to each IGBT, and the highest temperature may be selected and used. Furthermore, the temperature sensor 2 may be built in each IGBT. For example, a constant current may be passed through a pn junction for temperature detection provided on a semiconductor chip, and the voltage drop may be detected to generate a temperature signal. The IGBT temperature may be estimated from the detected ambient temperature and the current integration value of the IGBT. The temperature of the controller 3 may be detected and regarded as the IGBT temperature.

(Explanation of operation of controller 3)
Next, the operation of the controller 3 having a microcomputer configuration will be described with reference to the flowchart shown in FIG.

  The routine is started by applying the power supply voltage, and the internal state is reset and initialized (S100). At this time, the changeover switch 37 is turned off. Thereby, the output voltage of each voltage regulator 16-19 (power supply voltage of the drive circuits 10-15) becomes relatively small. Thereafter, the temperature T output from the temperature sensor 2 is read (S102), and the temperature T is compared with a predetermined threshold value Tth stored in advance (S104). A command to turn off is issued (S106), and a double drive is commanded to the drive circuits 10-15. Here, the double drive means an operation of driving both of the two complementary CMOS inverters 10a and 10b connected in parallel shown in FIG.

  If it is determined in step S104 that the temperature T is equal to or higher than the threshold value Tth, the switch 37 is instructed to be turned on (S108), and single drive is instructed to the drive circuits 10-15. Here, the single drive means an operation of driving only one of the two complementary CMOS inverters 10a and 10b connected in parallel shown in FIG. 4 or alternately.

  Thereby, when the temperature rises, the power supply voltage output from the voltage regulators 16 to 19 to the drive circuits 10 to 15 increases, and when the temperature decreases, the power supply voltage output from the voltage regulators 16 to 19 to the drive circuits 10 to 15 decreases. Therefore, with a simple circuit configuration, the gate voltage can be stabilized, the temperature rise of the IGBTs 4 to 9 can be suppressed, and the switching surge voltage can be suppressed.

  Further, when the power supply voltage output from the voltage regulators 16 to 19 to the drive circuits 10 to 15 rises when the temperature rises, the output impedance (output resistance) of the drive circuits 10 to 15 increases, so that the IGBTs 4 to 9 are turned on. The transient period is extended and the increase of the switching surge voltage is suppressed.

(Embodiment 2)
Next, the power supply voltage output from the voltage regulators 16 to 19 to the drive circuits 10 to 15 is changed in multiple steps or continuously according to the detected temperature, and the input power supply voltage applied to the voltage regulators 16 to 19 is changed accordingly. An example of control that is also changed in conjunction with the above will be described with reference to the flowchart shown in FIG.

  In this embodiment, the output voltages of the voltage regulators 16 to 19 can be changed continuously. Of course, this output voltage may be changed stepwise. In order to continuously change the output voltages of the voltage regulators 16 to 19, for example, a digital command value output from the controller 3 is D / A converted to generate an analog threshold voltage, which is used as a sample hold circuit. What is necessary is just to hold and apply to the negative input terminal of the comparator 31. Thereby, the output voltage of the voltage regulator 16 (power supply voltage of the drive circuit 10) can be continuously adjusted.

  In FIG. 6, the routine is started by applying the power supply voltage, and the internal state is reset and initialized (S200). Next, the temperature T output from the temperature sensor 2 is read (S202), and the optimum value of the output voltage of the voltage regulator 16 is obtained by substituting the temperature T into a previously stored map (S204). Next, it is checked whether or not Vu needs to be increased (S206). If necessary, the target voltage value in the PWM feedback control of the isolated power supply circuit described with reference to FIG. A level value is set (S208). As a result, the duty ratio of the PWM feedback control of the switch 22 increases, and the input power supply voltage input to the voltage regulators 16 to 19 by the power supply circuit of FIG. 2 increases.

  Next, if it is not necessary to increase Vu, it is checked whether or not Vu needs to be reduced (S210). If necessary, the target voltage value in the PWM feedback control of the isolated power supply circuit described with reference to FIG. The threshold value input to the comparator is set to a low level value (S212). As a result, the duty ratio of the PWM feedback control of the switch 22 decreases, and the input power supply voltage input to the voltage regulators 16 to 19 by the power supply circuit of FIG.

  In this way, in the output voltage range of the voltage regulators 16-19, the power supply circuit shown in FIG. 2 does not increase the input power supply voltage input to the voltage regulators 16-19, and the output possible voltage of the voltage regulators 16-19. Since this input power supply voltage is increased when the range is exceeded, the loss of the voltage regulators 16 to 19 can be reduced.

  In the above description, the input power supply voltage of the voltage regulators 16 to 19 is changed stepwise, but it is obvious that the voltage regulators 16 to 19 may be changed continuously according to the output voltage.

(Modification)
In each of the above embodiments, the temperature sensor 2 is shared, but the temperature sensor 2 may be separately provided in each of the IGBTs 4 to 9 and the voltage regulators 16 to 19 may be individually controlled according to the detected temperatures.

FIG. 3 is a circuit diagram illustrating a three-phase inverter circuit according to the first embodiment. FIG. 2 is a circuit diagram of a power supply circuit that outputs an input power supply voltage applied to the voltage regulator shown in FIG. 1. FIG. 2 is a circuit diagram of the voltage regulator shown in FIG. 1. FIG. 2 is a circuit diagram of the drive circuit shown in FIG. 1. It is a flowchart which shows operation | movement of the controller shown in FIG. 6 is a flowchart illustrating a control operation according to the second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Three-phase inverter circuit 2 Temperature sensor 3 Controller 10-15 Drive circuit 16-19 Voltage regulator 17 Voltage regulator 18 Voltage regulator 19 Voltage regulator 21 Battery 22-25 Diode 26-29 Capacitor 30 Current control transistor 31 Comparator 32 Resistance voltage dividing circuit 33 threshold voltage generation circuit 34 voltage dividing resistor 35 voltage dividing resistor 36 adjustment resistor 37 changeover switch 220 switch

Claims (8)

A power semiconductor switching element for switching a load current;
A drive circuit for applying a control voltage formed by at least current amplification of the input pulse signal voltage to the control electrode of the power semiconductor switching element;
In a power semiconductor switching circuit comprising:
A power supply voltage stabilizing circuit for creating a stabilized power supply voltage and applying the stabilized power supply voltage to the drive circuit;
A temperature detection circuit for detecting a temperature signal having a correlation with the temperature of the power semiconductor switching element;
A control circuit for changing the stabilized power supply voltage based on the detected temperature signal;
Have
The control circuit includes:
Instructing the power supply voltage stabilization circuit when the temperature is increased to increase the stabilized power supply voltage, thereby increasing the high level of the control voltage that the drive circuit outputs to the power semiconductor switching element, Instructing the power supply voltage stabilization circuit to reduce the stabilized power supply voltage when the temperature becomes low, thereby reducing the high level of the control voltage output from the drive circuit to the power semiconductor switching element. A semiconductor switching circuit for power. The power semiconductor switching circuit according to claim 1,
The power supply voltage stabilization circuit includes:
It consists of a voltage regulator that intermittently controls the power supply voltage applied to the drive circuit based on the comparison result of the divided output voltage and a predetermined threshold voltage,
The control circuit includes:
A power semiconductor switching circuit that changes at least one of the divided output voltage and the threshold voltage based on the temperature signal. The power semiconductor switching circuit according to claim 1,
Having a three-phase inverter circuit composed of six power semiconductor switching elements;
The power supply voltage stabilization circuit includes:
Three upper arm side voltage regulators for individually supplying power supply voltages to the three drive circuits for driving the power semiconductor switching elements on each phase upper arm side, and the power semiconductor switching elements on each phase lower arm side One lower arm side voltage regulator for individually supplying a power supply voltage to the three drive circuits for driving the power supply;
A power semiconductor switching circuit comprising: The power semiconductor switching circuit according to claim 3,
A total of four voltage regulators
A power semiconductor switching circuit controlled by the temperature signal from a common temperature detection circuit. The power semiconductor switching circuit according to claim 4,
The control circuit includes:
A power semiconductor that increases the input power supply voltage of the power supply voltage stabilization circuit when increasing the stabilized power supply voltage and decreases the input power supply voltage of the power supply voltage stabilization circuit when decreasing the stabilized power supply voltage Switching circuit. The power semiconductor switching circuit according to claim 5,
The control circuit includes:
A power semiconductor that increases the input power supply voltage of the power supply voltage stabilization circuit when increasing the stabilized power supply voltage and decreases the input power supply voltage of the power supply voltage stabilization circuit when decreasing the stabilized power supply voltage Switching circuit. The power semiconductor switching circuit according to claim 1,
The power semiconductor switching element has a control electrode composed of a gate electrode,
The control circuit substantially increases the output impedance of the drive circuit when increasing the stabilized power supply voltage, and substantially decreases the output impedance of the drive circuit when decreasing the stabilized power supply voltage. Power semiconductor switching circuit. The power semiconductor switching circuit according to claim 1,
A plurality of the drive circuits for driving the same power semiconductor switching elements in parallel by operating in parallel;
The control circuit stops a part of the plurality of drive circuits when increasing the stabilized power supply voltage, and operates all of the plurality of drive circuits when decreasing the stabilized power supply voltage. circuit.

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