JP2015130553A - inductive load drive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inductive load drive device capable of reducing fluctuations in load current breaking time by suppressing temperature fluctuations in an arc-extinguishing circuit.SOLUTION: A temperature detection circuit 11 detects a temperature of an arc-extinguishing circuit 7a by a thermistor 12 mounted near the arc-extinguishing circuit 7a. An arc-extinguishing control circuit 14 compares a temperature detection voltage Vt corresponding to a detection temperature with a reference voltage Vr corresponding to a threshold temperature using a comparator 17. When the detection voltage of the arc-extinguishing circuit 7a is less than the threshold temperature, the arc-extinguishing control circuit 14 selects the arc-extinguishing circuit 7a and connects to a load 2 by turning on a MOS transistor 8a of a switching circuit 8. When the detection voltage of the arc-extinguishing circuit 7a is not less than the threshold temperature, the arc-extinguishing control circuit 14 selects an arc-extinguishing circuit 7b and connects to the load 2 by turning on a MOS transistor 8b of the switching circuit 8.

Description

  The present invention relates to an inductive load driving device including an arc extinguishing circuit that reduces back electromotive force of an inductive load.

  The injector driving device includes a switching element in an energization path to an electromagnetic solenoid of the injector, and drives the switching element on and off according to an injection signal. Since the electromagnetic solenoid is an inductive load, when the switching element is driven off, a counter electromotive force (flyback voltage) is generated between the terminals of the electromagnetic solenoid. In view of this, the injector driving device includes an arc extinguishing circuit that energizes and reduces the counter electromotive force when the counter electromotive force is applied. Patent Document 1 describes a configuration in which a Zener diode is provided between a base and a collector of a switching element, and flyback energy is absorbed by the switching element.

As another form, there is used an arc extinguishing circuit configured by a series circuit of a resistor and a diode and connected in parallel with an electromagnetic solenoid. Extinguishing circuit of this embodiment, when the switching device is switched from ON to OFF, consumes stored energy LI ^2/2 at reflux the current flowing through the electromagnetic solenoid, by sharply reducing the current flowing through the solenoid Close the injector.

JP-A-8-121227

Since the arc suppression circuitry each time the injector drive unit on and off driving the switching elements consumes energy LI ^2/2, the temperature of the resistor and the diode constituting the extinguishing circuit increases the self-heating. As a result, the resistance value of the resistor and the forward voltage Vf of the diode change.

  When the resistance value and the forward voltage Vf change, the voltage value of the back electromotive force generated when the switching element is driven off changes, and the rate of reduction of the current flowing through the electromagnetic solenoid, in other words, the current is closed from the start of off driving. The time (shutoff time) until the valve start level is lowered changes. As a result, even if an injection signal having the same waveform is input, there is a problem that the fuel injection time changes due to self-heating. There is also a concern that the resistance value of the arc extinguishing circuit and the element deterioration of the diode proceed due to self-heating.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an inductive load driving device that reduces fluctuations in the interruption time of load current by suppressing temperature fluctuations in the arc-extinguishing circuit for back electromotive force. It is in.

  The inductive load driving device according to claim 1 is provided with a switch circuit provided in an energization path to the inductive load, a load control circuit for driving the switch circuit on and off, and an induction generated when the switch circuit is driven off. First to n-th (n: integer greater than or equal to 2) arc-extinguishing circuits having the same configuration that energizes and reduces the counter-electromotive force when a counter-electromotive force of the load is applied. Further, the inductive load driving device is provided between one end of each arc extinguishing circuit and one end of the inductive load, and a switching circuit that selects one of the arc extinguishing circuits and connects to the inductive load; A temperature detection circuit that detects at least the temperature of the first arc-extinguishing circuit and an arc-extinguishing control circuit that controls the switching circuit are provided.

  The arc extinguishing control circuit selects the first arc extinguishing circuit by the switching circuit when the detected temperature of the first arc extinguishing circuit is lower than the threshold temperature, and connects the inductive load to the first arc extinguishing circuit. When the detected temperature is equal to or higher than the threshold temperature, the switching circuit selects an arc extinguishing circuit other than the first arc extinguishing circuit and connects it to the inductive load.

  According to this configuration, while the detected temperature of the first arc-extinguishing circuit is lower than the threshold temperature, the other arc-extinguishing circuit is disconnected from the inductive load and the heat generation is stopped. The temperature drops. When the detected temperature of the first arc extinguishing circuit exceeds the threshold temperature due to heat generation, the first arc extinguishing circuit is disconnected from the inductive load, and another arc extinguishing circuit is selected and connected to the inductive load instead. Is done. The temperature of the other arc extinguishing circuit connected at this time is lowered for the reason described above. Since the first arc-extinguishing circuit stops generating heat, the temperature decreases. When the detected temperature falls below the threshold temperature, the first arc-extinguishing circuit is selected again instead of the other arc-extinguishing circuit. Connected to inductive load.

  In this way, when the temperature of the first arc-extinguishing circuit is equal to or higher than the threshold temperature, other arc-extinguishing circuits are substituted, so the temperature fluctuation of the arc-extinguishing circuit (selective arc-extinguishing circuit) connected to the inductive load Is smaller than the conventional configuration. As a result, the change in the characteristics (voltage, resistance, etc.) of the selective arc-extinguishing circuit becomes small, the fluctuation of the reduction rate of the load current at the time of off-drive, and the time from the start of off-drive until the current drops to a predetermined level ( The fluctuation of the cut-off time is reduced.

  According to the means of claim 2, the temperature detection circuit includes a temperature detection element mounted in the vicinity of the arc-extinguishing circuit that detects the temperature, and the constant voltage is divided by a series circuit of the resistor and the temperature detection element. Outputs temperature detection voltage. The arc extinguishing control circuit includes a comparator that compares a temperature detection voltage corresponding to the detected temperature of the first arc extinguishing circuit with a reference voltage corresponding to the threshold temperature. According to this configuration, the comparison between the detected temperature of the first arc-extinguishing circuit and the threshold temperature can be realized with a hardware configuration.

  According to a third aspect of the present invention, the temperature detection circuit includes a temperature detection element mounted in the vicinity of the arc-extinguishing circuit that detects the temperature, and the constant voltage is divided by the series circuit of the resistor and the temperature detection element. Outputs temperature detection voltage. The arc extinguishing control circuit inputs a temperature detection voltage corresponding to the detected temperature of the first arc extinguishing circuit after A / D conversion, and compares the detected temperature obtained from the input value with the threshold temperature. I have. According to this configuration, the comparison between the detected temperature of the first arc extinguishing circuit and the threshold temperature can be realized by a software configuration.

  According to a fourth aspect of the present invention, the temperature detection circuit detects the temperature of the first to nth arc extinguishing circuits. The arc extinguishing control circuit selects the arc extinguishing circuit having the lowest detected temperature from the second to nth arc extinguishing circuits by the switching circuit when the detected temperature of the first arc extinguishing circuit is equal to or higher than the threshold temperature. Connect to inductive load. According to this configuration, the temperature of the other arc-extinguishing circuit becomes lower while switching from the first arc-extinguishing circuit to the other arc-extinguishing circuit, so that the selective arc-extinguishing circuit connected to the inductive load Temperature fluctuation can be further suppressed.

  An inductive load driving device according to a fifth aspect includes a switch circuit, a load control circuit, first to n-th arc-extinguishing circuits, and a switching circuit similar to the inductive load driving device according to the first aspect. . Further, an inductive load is selected by selecting a temperature detecting circuit for detecting the temperature of the first to nth arc extinguishing circuits and an arc extinguishing circuit having the lowest detected temperature from the first to nth arc extinguishing circuits by the switching circuit. An arc-extinguishing control circuit is provided.

  According to this configuration, the temperature fluctuation of the selective arc-extinguishing circuit connected to the inductive load is smaller than that in the conventional configuration. As a result, the change in the characteristics (voltage, resistance, etc.) of the selective arc-extinguishing circuit becomes small, the fluctuation of the reduction rate of the load current at the time of off-drive, and the time from the start of off-drive until the current drops to a predetermined level ( The fluctuation of the cut-off time is reduced.

  According to the means of claim 6, the temperature detection circuit includes a temperature detection element mounted in the vicinity of each of the first to n-th arc extinguishing circuits, and a constant voltage is connected to the series circuit of the resistor and the temperature detection element. To divide the voltage and output a temperature detection voltage. The arc extinguishing control circuit includes a microcomputer that inputs the temperature detection voltage after A / D conversion and identifies the arc extinguishing circuit having the lowest detection temperature by comparing the detected temperatures obtained from the input values. According to this configuration, the selection process of the arc extinguishing circuit having the lowest detected temperature can be realized by a software configuration.

  According to a seventh aspect of the present invention, each of the first to nth arc extinguishing circuits includes a series circuit of a resistor and a diode. Since the resistor consumes energy, the reduction rate of the load current is increased and the interruption time is shortened.

The block diagram of the load drive device which shows 1st Embodiment Waveform diagram showing overall operation Back electromotive force and load current waveform diagram Configuration diagram of a load driving device showing a second embodiment Waveform diagram showing overall operation Flow chart of arc extinguishing control processing The block diagram of the load drive device which shows 3rd Embodiment Waveform diagram showing overall operation Flow chart of arc extinguishing control processing Flowchart of arc extinguishing control process showing the fourth embodiment

In each embodiment, substantially the same parts are denoted by the same reference numerals and description thereof is omitted.
(First embodiment)
A first embodiment will be described with reference to FIGS. 1 to 3. A load driving device 1 shown in FIG. 1 is mounted on, for example, an electronic control unit of a vehicle, and cuts off an inductive load 2 (hereinafter referred to as a load 2) such as an electromagnetic solenoid of an injector, thereby pulsing current. Shed. The load 2 is connected between the power line 3 of the voltage VB connected to a battery (not shown) and the output terminal 4 of the load driving device 1.

  An N-channel MOS transistor 5 that functions as a switch circuit is connected to the energization path between the output terminal 4 and the ground. The microcomputer 6 (hereinafter referred to as the microcomputer 6) outputs a drive signal Gs having an H level (on drive level) and an L level (off drive level) to the gate of the MOS transistor 5 to drive the load 2 on and off. It is a load control circuit. The microcomputer 6 operates with a constant control power supply voltage Vcc generated by a power supply circuit (not shown).

  Between the power supply line 3 and the output terminal 4 in the load driving device 1, a series circuit of a first arc extinguishing circuit 7a and an N channel MOS transistor 8a and a second arc extinguishing circuit 7b and an N channel MOS are provided. A series circuit with the transistor 8b is connected in parallel. The arc extinguishing circuits 7 a and 7 b have the same configuration including the constants of the elements, and are configured by a series circuit of a resistor 9 and a diode 10. The anode of the diode 10 and the drains of the MOS transistors 8a and 8b are connected with a polarity on the output terminal 4 side so that a return current flows when a counter electromotive force (flyback voltage) of the load 2 is applied. The MOS transistors 8a and 8b constitute a switching circuit 8 that selects any one of the arc-extinguishing circuits 7a and 7b and connects it to one end (output terminal 4) of the load 2.

  The temperature detection circuit 11 detects the temperature of the arc-extinguishing circuit 7a by a thermistor 12 (temperature detection element) mounted in the vicinity of the arc-extinguishing circuit 7a. As will be described later, since the heat generated by the resistor 9 is larger than the heat generated by the diode 10, the thermistor 12 is preferably disposed close to the resistor 9 on the mounting substrate. The temperature detection circuit 11 divides the power supply voltage Vcc by a series circuit of the resistor 13 and the thermistor 12 to output a temperature detection voltage Vt corresponding to the detected temperature. The thermistor 12 is of the NTC type and has a characteristic that the resistance value decreases as the temperature increases.

  The arc extinguishing control circuit 14 divides the power supply voltage Vcc by resistors 15 and 16 to generate a reference voltage Vr corresponding to the threshold temperature, and compares the temperature detection voltage Vt and the reference voltage Vr using the comparator 17. . The output terminal of the comparator 17 is pulled up to the power supply voltage Vcc by the resistor 18.

  The switching signal output from the comparator 17 becomes the drive signal Ga input to the gate of the MOS transistor 8a via the drive circuit 19, and the drive input to the gate of the MOS transistor 8b via the inverter 20 and the drive circuit 21. It becomes the signal Gb. As a result, either one of the MOS transistors 8a and 8b is turned on in response to the switching signal. The drive circuits 19 and 21 use the boost drive signal output from the microcomputer 6 to boost the voltage VB so that the drive signals Ga and Gb are sufficient to turn on the MOS transistors 8a and 8b. It has a circuit.

  Next, the operation of the present embodiment will be described with reference to FIGS. FIG. 2 shows the drive signal Gs, the reference voltage Vr, the temperature detection voltage Vt, the drive signals Ga and Gb, and the selected extinguishing when the microcomputer 6 outputs the drive signal Gs having a fixed cycle with a duty ratio of 50%. The waveforms of the circuit and the output voltage Vout (voltage at the terminal 4) are shown. For convenience of explanation, the temperature change rate of the arc extinguishing circuit 7a is drawn larger than actual.

  When the switching signal output from the comparator 17 is at the H level, the MOS transistor 8a is turned on, the MOS transistor 8b is turned off, and the arc-extinguishing circuit 7a is selected and connected to the load 2. When the switching signal is at the L level, the MOS transistor 8a is turned off, the MOS transistor 8b is turned on, and the arc extinguishing circuit 7b is selected and connected to the load 2. In the following description, the arc extinguishing circuit connected to the load 2 is referred to as a selective arc extinguishing circuit.

  When the drive signal Gs becomes H level, the MOS transistor 5 is turned on (energized state), and the load current flowing from the power supply line 3 through the load 2, the output terminal 4, and the MOS transistor 5 increases from zero. When the drive signal Gs becomes L level, the MOS transistor 5 is turned off (disconnected state), and a back electromotive force is generated in the load 2. Due to this counter electromotive force, the load current flows back from the power supply line 3 through the load 2, the output terminal 4, the MOS transistor 8a or 8b, and the arc extinguishing circuit 7a or 7b.

  When the load current returns to the selective arc-extinguishing circuit, energy is mainly consumed by the resistor 9, so that the return current rapidly decreases to zero. At the same time, the back electromotive force is reduced to zero, and the output voltage Vout returns to VB. When the on / off driving of the load 2 is repeated, the temperature of the selective arc-extinguishing circuit rises due to heat generated by the selective arc-extinguishing circuit.

  FIG. 3 shows waveforms of the back electromotive force and the load current when the temperature of the arc extinguishing circuit 7a changes. The temperature coefficient of the resistor 9 constituting the arc extinguishing circuit 7a may be positive or negative depending on the type. The forward voltage Vf of the diode 10 decreases as the temperature increases. Since the voltage applied to the arc-extinguishing circuit 7a is mainly borne by the resistor 9, the magnitude of the back electromotive force applied to the arc-extinguishing circuit 7a when the MOS transistor 5 is turned off is mainly the resistance value of the resistor 9. It depends on.

As shown by the broken line in FIG. 3, when the resistance value of the resistor 9 increases, the voltage drop increases and the back electromotive force generated in the load 2 increases. Therefore, the power consumed by the arc-extinguishing circuit 7a increases and the load 2 is energized. reduction ratio of accumulated was LI ^2/2 energy (flyback energy) increases. As a result, the time from when the MOS transistor 5 is turned off to when the load current decreases to a predetermined level (for example, a level at which valve closing is started) is shortened.

  On the other hand, when the resistance value of the resistor 9 becomes small, as shown by a one-dot chain line in FIG. 3, the counter electromotive force generated in the load 2 becomes low and the energy reduction rate becomes small, so that the interruption time becomes long. That is, since the cutoff time changes according to the temperature fluctuation of the arc extinguishing circuit 7a, for example, in an injector provided with an electromagnetic solenoid, the injection time changes due to the temperature fluctuation of the arc extinguishing circuit 7a.

  When the temperature detection voltage Vt is higher than the reference voltage Vr, that is, when the temperature of the arc extinguishing circuit 7a is lower than the threshold temperature, the arc extinguishing control circuit 14 turns on the MOS transistor 8a and selects the arc extinguishing circuit 7a selectively. Used as an arc circuit. During this time, the arc extinguishing circuit 7b is disconnected from the load 2 and heat generation stops, so that the temperature of the arc extinguishing circuit 7b decreases. When the arc extinguishing circuit 7a generates heat by the on / off driving of the load 2 and its temperature becomes equal to or higher than the threshold temperature (time t1), the temperature detection voltage Vt becomes equal to or lower than the reference voltage Vr. The arc extinguishing control circuit 14 turns on the MOS transistor 8b instead of the MOS transistor 8a and uses the arc extinguishing circuit 7b as a selective arc extinguishing circuit. The temperature of the arc extinguishing circuit 7b at the time of switching is lower than the threshold temperature.

  Since the arc extinguishing circuit 7a stops generating heat, the temperature gradually decreases. When the temperature of the arc extinguishing circuit 7a becomes lower than the threshold temperature (time t2), the temperature detection voltage Vt becomes higher than the reference voltage Vr. The arc extinguishing control circuit 14 turns on the MOS transistor 8a instead of the MOS transistor 8b, and uses the arc extinguishing circuit 7a again as a selective arc extinguishing circuit. That is, the arc-extinguishing control circuit 14 uses the arc-extinguishing circuit 7a as a selective arc-extinguishing circuit, and uses the arc-extinguishing circuit 7b as a selective arc-extinguishing circuit only when the temperature of the arc-extinguishing circuit 7a is equal to or higher than the threshold temperature.

  According to the present embodiment described above, the temperature of the selective arc extinguishing circuit connected to the load 2 is maintained below the threshold temperature, and the fluctuation range becomes small. As a result, the change in the characteristics of the selective arc-extinguishing circuit having temperature dependence (particularly the resistance value of the resistor 9) is reduced, and the variation in the reduction rate of the load current when the MOS transistor 5 is driven off, and hence the variation in the cut-off time. Get smaller. Therefore, for example, when the load driving device 1 is applied to an injector driving device, it is possible to suppress fluctuations in the injection time due to the temperature rise of the arc extinguishing circuit 7a when fuel injection is repeated. Furthermore, by maintaining the temperature of the arc extinguishing circuits 7a and 7b below the threshold temperature, it is possible to suppress the progress of element degradation of the resistor 9 and the diode 10 due to self-heating.

(Second Embodiment)
A second embodiment will be described with reference to FIGS. The load driving device 31 shown in FIG. 4 includes an arc extinguishing control circuit 32 that performs a comparison process between the detected temperature of the arc extinguishing circuit 7a and the threshold temperature by the microcomputer 6. The microcomputer 6 has a built-in A / D converter, and A / D converts and inputs the temperature detection voltage Vt output from the temperature detection circuit 11. The microcomputer 6 outputs complementary drive signals Ga and Gb to the drive circuits 19 and 21 from the output port. Other configurations are the same as those of the load driving device 1 shown in FIG.

  FIG. 5 shows the drive signal Gs, temperature detection voltage Vt, drive signals Ga and Gb, selected arc-extinguishing circuit and output voltage when the microcomputer 6 outputs the drive signal Gs having a constant cycle with a duty ratio of 50%. The waveform of Vout is shown. FIG. 6 shows a flow of the arc extinguishing control process executed by the microcomputer 6.

  When the microcomputer 6 starts processing, first, the MOS transistor 8a is turned on to select the arc extinguishing circuit 7a (step S1). The microcomputer 6 A / D converts the temperature detection voltage Vt to obtain the temperature of the arc extinguishing circuit 7a (step S2), and determines whether or not the detected temperature is equal to or higher than a threshold temperature (step S3). While the detected temperature is lower than the threshold temperature, the processes in steps S2 and S3 are repeated with the arc extinguishing circuit 7a selected.

  When the detected temperature becomes equal to or higher than the threshold temperature, the microcomputer 6 turns on the MOS transistor 8b instead of the MOS transistor 8a and selects the arc extinguishing circuit 7b (step S4). Since the arc extinguishing circuit 7a stops generating heat, the temperature gradually decreases. The microcomputer 6 A / D converts the temperature detection voltage Vt to obtain the temperature of the arc extinguishing circuit 7a (step S5), and determines whether or not the detected temperature is lower than the threshold temperature (step S6). While the detected temperature is equal to or higher than the threshold temperature, the processes of steps S5 and S6 are repeated with the arc extinguishing circuit 7b selected. When the detected temperature becomes lower than the threshold temperature, the MOS transistor 8a is turned on instead of the MOS transistor 8b to select the arc extinguishing circuit 7a (step S7), and the process proceeds to step S2. Since the arc extinguishing circuit 7b stops generating heat, the temperature gradually decreases.

  Also with the load driving device 31 of this embodiment, the temperature of the selective arc-extinguishing circuit connected to the load 2 is maintained below the threshold temperature, and the temperature fluctuation range is reduced. Therefore, the same effect as the first embodiment can be obtained.

(Third embodiment)
A third embodiment will be described with reference to FIGS. The load driving device 41 shown in FIG. 7 includes a MOS transistor 5, arc extinguishing circuits 7a, 7b, 7c, a switching circuit 8 including MOS transistors 8a, 8b, 8c, temperature detection circuits 11a, 11b, 11c, and an arc extinguishing control circuit 42. It has.

  The arc-extinguishing circuits 7a, 7b, 7c and the switching circuit 8 are connected in the same manner as the load driving devices 1, 31. The temperature detection circuits 11a, 11b, and 11c are configured in the same manner as the above-described temperature detection circuit 11, and detect the temperatures of the arc extinguishing circuits 7a, 7b, and 7c (especially the resistor 9), respectively, to detect the temperature detection voltages Vt1 and Vt2. , Vt3 is output. The microcomputer 6 included in the arc extinguishing control circuit 42 performs A / D conversion on the temperature detection voltages Vt1, Vt2, and Vt3 and inputs the drive signals Ga, Gb, and Gc from the output ports. The drive signals Ga, Gb, and Gc are given to the gates of the MOS transistors 8a, 8b, and 8c through the drive circuits 19, 21, and 43, respectively.

  FIG. 8 shows that the drive signal Gs, temperature detection voltages Vt1, Vt2, and Vt3, and drive signals Ga, Gb, and Gc when the microcomputer 6 outputs the drive signal Gs having a fixed cycle with a duty ratio of 50% are selected. The waveforms of the arc extinguishing circuit and the output voltage Vout are shown. FIG. 9 shows a flow of the arc extinguishing control process executed by the microcomputer 6.

  When the microcomputer 6 starts processing, first, one of the MOS transistors 8a, 8b, and 8c is turned on to select one of the arc extinguishing circuits 7a, 7b, and 7c (step T1). At this time, it is preferable to select an arc extinguishing circuit having the lowest detected temperature. In the waveform example shown in FIG. 8, the arc extinguishing circuit 7a is selected. The microcomputer 6 A / D converts the temperature detection voltages Vt1, Vt2, and Vt3 to obtain the temperatures of the arc extinguishing circuits 7a, 7b, and 7c (step T2), and compares these detection temperatures with each other to detect the lowest temperature. An arc extinguishing circuit is specified (step T3).

  Subsequently, it is determined whether or not the specified arc extinguishing circuit is the same as the current selective arc extinguishing circuit (step T4). When the specified arc-extinguishing circuit is different from the current selective arc-extinguishing circuit, the drive signals Ga, Gb, Gc are output so that only the identified arc-extinguishing circuit is connected to the load 2, and the MOS transistors 8a, 8b, 8c is switched and it transfers to step T2 (step T5; time t1, t2, t3 shown in FIG. 8). If the specified arc-extinguishing circuit is the same as the current selective arc-extinguishing circuit, step T5 is skipped and the process proceeds to step T2.

  According to the load driving device 41 of the present embodiment, since the arc extinguishing circuits 7a, 7b, 7c having the lowest temperature are used as the selective arc extinguishing circuit, the temperature fluctuation of the selective arc extinguishing circuit connected to the load 2 is further reduced. Become. In addition, the same effects as those of the first embodiment can be obtained.

(Fourth embodiment)
A fourth embodiment will be described with reference to FIG. The load drive device of this embodiment has the same hardware configuration as the load drive device 41 shown in FIG. The arc extinguishing control process executed by the microcomputer 6 constituting the load driving device is a modification of the arc extinguishing control process described in the second embodiment.

  The microcomputer 6 executes the processing from steps S1 to S3 (see FIG. 6) as in the second embodiment. When the detected temperature of the arc extinguishing circuit 7a becomes equal to or higher than the threshold temperature, the microcomputer 6 performs A / D conversion on the temperature detection voltages Vt2 and Vt3 to obtain the temperatures of the arc extinguishing circuits 7b and 7c (step S11). The microcomputer 6 identifies the arc extinguishing circuit having the lowest detected temperature among the arc extinguishing circuits 7b and 7c, turns off the MOS transistor 8a, and turns on the MOS transistor 8b or 8c to select the identified arc extinguishing circuit (step). S12). Thereafter, similarly to the second embodiment, steps S5 to S7 (see FIG. 6) are executed.

  According to the present embodiment, while the arc-extinguishing circuit 7a is switched to the other arc-extinguishing circuit 7b or 7c, the temperature of the other arc-extinguishing circuit becomes lower, so that the selective arc-extinguishing connected to the load 2 is performed. The temperature fluctuation of the circuit is further reduced. In addition, the same effects as those of the first embodiment can be obtained.

(Other embodiments)
As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to embodiment mentioned above, A various deformation | transformation and expansion | extension can be performed within the range which does not deviate from the summary of invention.

In each embodiment, the configuration including two or three arc extinguishing circuits 7a, 7b, and 7c has been described. However, the number of arc extinguishing circuits may be further increased.
The arc extinguishing circuits 7a, 7b, and 7c are not limited to the series circuit of the resistor 9 and the diode 10 as long as flyback energy is consumed.

  Hysteresis control may be performed in the detected temperature comparison process in each embodiment. Thereby, the switching frequency of the switching circuit 8 can be reduced.

  In the drawing, 1, 31, 41 are inductive load driving devices, 2 is an inductive load, 5 is a MOS transistor (switch circuit), 6 is a microcomputer (load control circuit), 7a, 7b, 7c are arc extinguishing circuits, 8 is a switching circuit, 9 is a resistor, 10 is a diode, 11, 11a, 11b, and 11c are temperature detection circuits, 12 is a thermistor (temperature detection element), 14, 32, and 42 are arc extinguishing control circuits, and 17 is a comparator. .

Claims (7)

A switch circuit (5) provided in the energization path to the inductive load (2);
A load control circuit (6) for driving the switch circuit on and off;
The first to nth (n: integer greater than or equal to 2) of the same configuration that energizes and reduces the counter electromotive force when the counter electromotive force of the inductive load generated when the switch circuit is driven off is applied. Arc extinguishing circuit (7a, 7b, 7c),
A switching circuit (8) provided between one end of each arc-extinguishing circuit and one end of the inductive load, and selecting one of the arc-extinguishing circuits and connecting to the inductive load;
A temperature detection circuit (11, 11a to 11c) for detecting a temperature of at least the first arc-extinguishing circuit;
When the detected temperature of the first arc-extinguishing circuit is lower than a threshold temperature, the switching circuit selects the first arc-extinguishing circuit and connects it to the inductive load, and the detection of the first arc-extinguishing circuit An arc extinguishing control circuit (14, 32, 42) for selecting an arc extinguishing circuit other than the first arc extinguishing circuit by the switching circuit and connecting to the inductive load when the temperature is equal to or higher than the threshold temperature; An inductive load driving device comprising: The temperature detection circuit includes a temperature detection element (12) mounted in the vicinity of the arc-extinguishing circuit for detecting temperature, and a constant voltage is divided by a series circuit of a resistor and the temperature detection element to generate a temperature detection voltage. Output,
The arc extinguishing control circuit (14) includes a comparator (17) that compares a temperature detection voltage corresponding to the detected temperature of the first arc extinguishing circuit and a reference voltage corresponding to the threshold temperature. The inductive load driving device according to claim 1. The temperature detection circuit includes a temperature detection element (12) mounted in the vicinity of the arc-extinguishing circuit for detecting temperature, and a constant voltage is divided by a series circuit of a resistor and the temperature detection element to generate a temperature detection voltage. Output,
The arc extinguishing control circuit (32) inputs a temperature detection voltage corresponding to the detected temperature of the first arc extinguishing circuit after A / D conversion, and the detected temperature obtained from the input value and the threshold temperature The inductive load driving device according to claim 1, further comprising a microcomputer for comparing with the microcomputer. The temperature detection circuits (11a to 11c) detect the temperatures of the first to nth arc extinguishing circuits,
When the detected temperature of the first arc-extinguishing circuit is equal to or higher than the threshold temperature, the arc-extinguishing control circuit (42) has the highest detected temperature among the second to n-th arc-extinguishing circuits by the switching circuit. 2. The inductive load driving device according to claim 1, wherein a low arc extinguishing circuit is selected and connected to the inductive load. A switch circuit (5) provided in the energization path to the inductive load (2);
A load control circuit (6) for driving the switch circuit on and off;
The first to nth (n: integer greater than or equal to 2) of the same configuration that energizes and reduces the counter electromotive force when the counter electromotive force of the inductive load generated when the switch circuit is driven off is applied. Arc extinguishing circuit (7a, 7b, 7c),
A switching circuit (8) provided between one end of each arc-extinguishing circuit and one end of the inductive load, and selecting one of the arc-extinguishing circuits and connecting to the inductive load;
A temperature detection circuit (11a-11c) for detecting the temperature of the first to nth arc extinguishing circuits;
An arc extinguishing control circuit (42) for selecting an arc extinguishing circuit having the lowest detected temperature from the first to nth arc extinguishing circuits by the switching circuit and connecting to the inductive load. Inductive load driving device. The temperature detection circuit includes a temperature detection element (12) mounted in the vicinity of each of the first to n-th arc extinguishing circuits, and divides a constant voltage by a series circuit of a resistor and the temperature detection element. Outputs temperature detection voltage,
The arc extinguishing control circuit (42) inputs the temperature detection voltage after A / D conversion, compares the detected temperatures obtained from the input values with each other, and identifies the arc extinguishing circuit with the lowest detected temperature. 6. The inductive load driving device according to claim 5, further comprising (6).   The inductivity according to any one of claims 1 to 6, wherein each of the first to nth arc extinguishing circuits is constituted by a series circuit of a resistor (9) and a diode (10). Load drive device.

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