JP2018007090A - Inductive load drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inductive load drive circuit capable of protecting a semiconductor switch in a case where a circuit ground and a ground are disconnected, the inductive load drive circuit being configured to protect the semiconductor switch in the case of battery reverse connection.SOLUTION: An inductive load drive circuit 10 comprises a protection circuit 13 which is connected between an output terminal S of a semiconductor switch element 12 and a ground line Lg and protects the semiconductor switch element 12. The protection circuit 13 includes: a protection switch Q1 which is connected in series to a reflux diode D1 and turned off in the case of reverse connection of a battery Ba to block a flow of a current from the battery through the reflux diode D1 to the semiconductor switch element 12; and a cutoff circuit 14 which turns off the protection switch Q1 in response to disconnection in the case where the ground line Lg and a ground Eth are disconnected.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an inductive load drive circuit, and more particularly, to a technique for protecting a semiconductor switch element provided in an inductive load drive circuit and switching energization to an inductive load.

  Conventionally, for example, a technique disclosed in Patent Document 1 is known as a technique for protecting a semiconductor switch element provided in an inductive load drive circuit and switching energization to an inductive load. In this document, an N-channel MOSFET (semiconductor switch element) is protected from inductive energy by circulating inductive energy generated when the inductive load is turned off by a free-wheeling diode connected in parallel with the load from the ground (GND). Have been described. Further, it is described that a semiconductor switch is connected in series with a free-wheeling diode, and the semiconductor switch is protected from the reverse connection of the battery by turning off the transistor when the battery is reversely connected.

JP 2010-044521 A

  However, when the inductive load drive circuit is for in-vehicle use etc., the ground terminal of the inductive load drive circuit is disconnected due to the vibration of the vehicle, etc., and the ground of the inductive load drive circuit is floating from the ground (ground) It is possible to become. In this case, in the configuration of the above document, the semiconductor switch element is once turned off as the ground potential rises, and then the inductive load driving circuit is connected via the free-wheeling diode and the protection transistor when the battery is reversely connected. It is conceivable that the semiconductor switch is turned on again when the ground potential is set to a low predetermined value. When the semiconductor switch is turned on again, it is conceivable that the ground potential rises due to the rise of the cathode potential of the freewheeling diode and the semiconductor switch is turned off again. That is, when the ground of the inductive load driving circuit is in a floating state, it is considered that an oscillation state in which the semiconductor switch element is repeatedly turned on and off is generated. When the oscillation state occurs, there is a possibility that the semiconductor switch element is damaged by applying a voltage exceeding the breakdown voltage generated when the semiconductor switch element is turned off to the semiconductor switch element a plurality of times.

  The technology disclosed in the present specification has been completed based on the above circumstances, and in an inductive load drive circuit having a configuration for protecting a semiconductor switch element when a battery is reversely connected, a circuit ground and a ground An inductive load driving circuit capable of protecting a semiconductor switch element when the connection to the device is cut off.

An inductive load driving circuit disclosed in the present specification controls a semiconductor switch element provided between a battery and an inductive load, and switching between energization and non-energization of the semiconductor switch element to the inductive load. A control circuit, a ground line connected to ground, and a protection circuit connected between the output terminal of the semiconductor switch element and the ground line, and protecting the semiconductor switch element, the free wheel diode, A protection switch that is connected in series to the free-wheeling diode and is turned off when the battery is reversely connected to prevent a current flow from the battery to the semiconductor switch element via the free-wheeling diode, and The protection circuit turns off the protection switch in response to the disconnection when the connection between the ground line and the ground is disconnected. Including blocking circuit which.
According to this configuration, when the disconnection of the connection between the ground line and the ground occurs or when the circuit ground floats, the protection switch is turned off in response to the disconnection. As a result, when the circuit ground floats, the potential of the circuit ground can be kept high, and the semiconductor switch element is prevented from being turned on / off by the control circuit, that is, the oscillation state of the semiconductor switch element is not generated. it can. Accordingly, in the inductive load drive circuit having a configuration (protection switch) for protecting the semiconductor switch element when the battery is reversely connected, the semiconductor switch element can be protected when the connection between the circuit ground and the ground is disconnected. Here, “when the connection between the circuit ground and the ground is disconnected” includes a state where the circuit ground is lifted from the ground.

In the inductive load driving circuit, the control circuit has a function of turning off the semiconductor switch element in response to the disconnection, and the cutoff circuit delays an off timing for turning off the protection switch from the disconnection timing. The inductive load driving circuit may include a Zener diode connected between a power supply line and the ground line.
According to this configuration, it is possible to prevent the voltage applied to the semiconductor switch element from exceeding the breakdown voltage of the semiconductor switch element due to the reverse voltage generated when the connection between the ground line and the ground is disconnected. Thereby, when the circuit ground is floated, the semiconductor switch can be reliably protected. That is, when the semiconductor switch element is turned off due to the disconnection between the ground line and the ground, a reverse voltage is generated by the inductive load, but the protection circuit is turned on by the delay circuit at the reverse voltage generation timing. As a result, the voltage applied to the semiconductor switch element can be prevented from exceeding the breakdown voltage by the Zener voltage of the Zener diode.

In the inductive load driving circuit, the control circuit has a function of performing a reset operation in response to the disconnection, and the delay period of the off timing by the delay circuit is determined from the disconnection timing to the reset operation. It may be set shorter than the period until the completion timing.
According to this configuration, it is possible to prevent the semiconductor switch element from being turned on after the reset operation of the control circuit is completed, thereby reliably preventing the oscillation operation of the semiconductor switch element.

Further, in the inductive load driving circuit, the cutoff circuit includes a switch circuit that turns off the protection switch in response to the disconnection and turns off the protection switch when the battery is reversely connected, and the delay circuit includes: The timing for turning off the protection switch by the switch circuit may be delayed.
According to this configuration, the switch circuit can turn off the protection switch when the battery is reversely connected and delay the protection switch when the connection between the ground line and the ground is disconnected.

In the inductive load driving circuit, the delay circuit may be configured by a parallel circuit of a capacitor and a resistor.
According to this configuration, the delay circuit can be realized with a simple circuit configuration.

The inductive load driving circuit may include a notification circuit that detects the disconnection of the connection between the ground line and the ground and notifies the disconnection.
According to this configuration, by notifying the user of the disconnection of the connection between the ground line and the ground, the user can quickly take a countermeasure for the disconnection.

  According to the inductive load driving circuit disclosed in the present specification, when the connection between the circuit ground and the ground is disconnected in the inductive load driving circuit having a configuration for protecting the semiconductor switch element when the battery is reversely connected, The semiconductor switch element can be protected.

Schematic block diagram of an inductive load driving circuit according to an embodiment Time chart for operation of inductive load drive circuit

<Embodiment>
The embodiment will be described with reference to FIGS.
1. Configuration of Inductive Load Drive Circuit As shown in FIG. 1, the inductive load drive circuit 10 includes a control circuit 11, a semiconductor switch element 12, a protection circuit 13, a notification circuit 16, a Zener diode ZD1, and the like. Here, the inductive load drive circuit 10 is mounted on an automobile and is connected between the battery Ba and an inductive load 50, for example, an FAN drive motor M for cooling the engine, and drives and controls the inductive load 50.

  The control circuit 11 is configured by a microcomputer, for example, and controls the switching (ON / OFF) operation of the semiconductor switch element 12 by, for example, a PWM (pulse width modulation) signal output from the control port PC1. At that time, the control circuit 11 appropriately changes the duty ratio (pulse width) of the PWM signal in accordance with the inductive load 50. Further, the control circuit 11 outputs a protection circuit control signal Sg1 described later from the control port PC2 to control the protection circuit 13. The control circuit 11 is activated in response to the operation of the external switch SW.

  For example, when the ground line LE that connects the ground line Lg and the ground (earth) Eth is disconnected from the ground terminal Jg and the connection between the ground line Lg and the ground Eth is disconnected, the control circuit 11 disconnects the ground line LE. More specifically, the semiconductor switch element 12 has a function of turning off in response to the potential of the ground line Lg being raised to a predetermined value and a function of performing a reset operation (initialization operation). Hereinafter, disconnection of the connection between the ground line Lg and the ground Eth may be simply referred to as “disconnection of ground (GND)”. “Out of ground” includes a floating state of the ground line Lg from the ground Eth.

  The semiconductor switch element 12 is provided between the battery Ba and the inductive load 50, and is configured by, for example, an N-channel MOSFET including a parasitic diode 12A as shown in FIG. When the battery Ba is normally connected, the semiconductor switch element 12 switches between energization and de-energization of the inductive load 50 according to the PWM signal supplied from the control port PC1 to the gate G, and the battery Ba. Is reversely connected, energization in the direction opposite to that when the battery Ba is normally connected is enabled via the parasitic diode 12A.

  As shown in FIG. 1, the protection circuit 13 is connected between the source S that is the output terminal of the semiconductor switch element 12 and the ground line Lg, and protects the semiconductor switch element 12. The protection circuit 13 includes a freewheeling diode D1, an N-channel MOSFET (Q1), a cutoff circuit 14, and the like. An N-channel MOSFET (Q1) (hereinafter simply referred to as “transistor Q1”) is an example of a protection switch. Specifically, the source S of the semiconductor switch element 12 is connected to the output line Lo, and the output line Lo is connected to the output terminal Jo connected to the inductive load 50.

  The anode A of the free-wheeling diode D1 is connected to the source S of the transistor Q1, and the cathode K of the free-wheeling diode D1 is connected to the source S of the semiconductor switch element 12 and the inductive load 50 via the output line Lo.

  The transistor Q1 is connected in series to the freewheeling diode D1, and is turned off when the battery Ba is reversely connected to prevent a current flow from the battery Ba to the semiconductor switching element 12 via the freewheeling diode D1. Specifically, when the battery Ba is reversely connected, the P-channel MOSFET (Q3), which will be described later, is turned off.

  The source S of the transistor Q1 is connected to the anode A of the freewheeling diode D1, the drain D is connected to the ground line Lg, and the gate G is connected to the cutoff circuit 14 through the resistor R2. A resistor R1 is connected between the drain and source of the transistor Q1. When the power to the inductive load driving circuit 10 is turned on, the transistor Q1 is turned on by a bias voltage generated by the resistor R1 and the resistor R2. Thereafter, the transistor Q1 is kept on except when the battery Ba is reversely connected and when the ground potential Vgnd rises due to the occurrence of a ground disconnection described later.

  That is, in the protection circuit 13, when the batteries Ba and GND are normally connected, the flow-through diode D1 prevents the load current from flowing into the protection circuit 13. When the battery Ba and GND are normally connected, when the semiconductor switch element 12 is switched from energization to non-energization by the semiconductor switch element 12, the surge current due to the counter electromotive voltage of the inductive load 50 is changed to the transistor Q1 and It can be refluxed through a reflux circuit constituted by the reflux diode D1. Thereby, the semiconductor switch element 12 can be protected from a surge.

  On the other hand, when the battery Ba is reversely connected, the transistor Q1 is turned off and the protection circuit (reflux circuit) 13 does not conduct. Therefore, a current in the reverse direction to that when the battery is normally connected flows through the inductive load 50 and the parasitic diode 12A. At this time, a predetermined current depending on the resistance value of the inductive load 50 flows, and a large current such as a short current does not occur in the inductive load driving circuit 10. Therefore, it is possible to protect the semiconductor switch element 12 and the wiring when the battery is reversely connected.

  Further, when the connection between the ground line Lg and the ground Eth occurs, for example, when the ground line LE connecting the ground line Lg and the ground Eth is disconnected from the ground terminal Jg, the cutoff circuit 14 The transistor Q1 is turned off in response to the disconnection.

  As shown in FIG. 1, the cutoff circuit 14 includes, for example, an NPN bipolar transistor Q2, a P-channel MOSFET (Q3), a delay circuit 15, and the like.

  The base B of the NPN bipolar transistor Q2 (hereinafter simply referred to as “transistor Q2”) is connected to the control port PC2 of the control circuit 11 through the resistor R3, and the transistor from the control circuit 11 through the P-channel MOSFET (Q3). A protection circuit control signal Sg1 for controlling on / off of Q1 is received. The emitter E of the transistor Q2 is connected to the ground line Lg, and a resistor R4 is connected between the base and the emitter. The collector C of the transistor Q2 is connected to the P-channel MOSFET (Q3) and the delay circuit 15 through the resistor R5.

  The gate G of a P-channel MOSFET (Q3; hereinafter simply referred to as “transistor Q3”) is connected to the collector C of the transistor Q2 via the resistor R5, and the drain D of the transistor Q3 is connected to the transistor Q1 via the resistor R2. Connected to the gate G. The source S of the transistor Q3 is connected to the battery Ba via a rectifier diode D2, a fuse Fs, and the like. A delay circuit 15 is connected between the source and gate of the transistor Q3. The transistor Q3 is an example of a switch circuit, and turns off the transistor Q1 in response to the ground disconnection and turns off the transistor Q1 when the battery Ba is reversely connected.

  In the present embodiment, the delay circuit 15 is configured by a parallel circuit of a capacitor C1 and a resistor R6 (an example of “resistor”), as shown in FIG. Therefore, the delay circuit 15 can be realized with a simple circuit configuration.

  The delay circuit 15 has a function of delaying the off timing (time t1 in FIG. 2) for turning off the transistor Q1 by the transistor Q2 from the timing (time t0) out of the ground when the transistor Q2 is off the ground (time t0 in FIG. 2). The delay period K3 of the off timing is set shorter than the period K4 from the timing of deviating from ground (time t0) to the completion timing of reset operation of the control circuit 11 (time t3) (see FIG. 2). In other words, the end timing (time t2) of the delay period K3 is set to be earlier than the completion timing (time t3) of the reset operation. As described later, this setting prevents the semiconductor switch element 12 from being turned on again after the ground is removed.

A Zener diode ZD1 is connected between the power supply line Ls and the ground line Lg. As a result, the drain-source voltage ΔV1 of the semiconductor switch element 12 when the semiconductor switch element 12 is turned off while the transistor Q1 after turning off the ground is turned on,
ΔV1p = VZD + Vf1 + Vf2
(See time t1 in FIG. 2). Here, the peak value ΔV1p is the peak value of the drain-source voltage ΔV1, VZD is the Zener voltage of the Zener diode ZD1, Vf1 is the forward voltage drop of the freewheeling diode D1, and Vf2 is the forward voltage of the rectifier diode D2. Directional voltage drop. By setting the Zener voltage VZD to a predetermined value, the peak value ΔV1p can be prevented from exceeding the withstand voltage Vmax of the semiconductor switch element 12.

  The notification circuit 16 detects the disconnection between the ground line Lg and the ground Eth and notifies the disconnection. As shown in FIG. 1, the notification circuit 16 includes, for example, a light emitting diode LED1 and an N-channel MOSFET (Q4; hereinafter, simply referred to as “transistor Q4”).

  The anode of the light emitting diode LED1 is connected to the battery Ba via the resistor R7, and the cathode of the light emitting diode LED1 is connected to the drain D of the transistor Q4. The gate G of the transistor Q4 is connected to the ground line Lg via the resistor R8, and the source S of the transistor Q4 is connected to the ground Eth.

  When the ground line Lg is disconnected from the ground Eth (see time t0 in FIG. 2), the ground potential Vgnd rises, and accordingly, the transistor Q4 is turned on and the light emitting diode LED1 emits light. Thereby, disconnection of the connection between the ground line Lg and the ground Eth is detected, and the disconnection is notified to the user. In this manner, by notifying the user of the disconnection of the connection between the ground line Lg and the ground Eth, the user can quickly take a countermeasure for the disconnection.

2. Operation of Inductive Load Drive Circuit When Ground is Off Next, the operation of the inductive load drive circuit 10 according to the ground off will be described with reference to the time chart of FIG. In FIG. 2, ΔV1 is the drain-source voltage of the semiconductor switch element 12, ΔV2 is the voltage between the ground Eth and the cathode K of the freewheeling diode D1 (in other words, the potential of the output line Lo), and ΔV3 is the gate of the transistor Q3. -Indicates a source-to-source voltage Vgs. Vgnd represents the potential of the ground line Lg (ground potential), and Sg1 represents a protection circuit control signal.
Further, a thick broken line after the timing of off-ground (time t0) indicates an example in the case where the cutoff circuit 14 is not provided. Note that when the cutoff circuit 14 is not provided, the gate G of the transistor Q1 is connected to the cathode of the rectifier diode D2 via the resistor R2.

  Now, assume that at time t0 in FIG. 2, a ground loss occurs during a period in which ΔV1 is 0 (zero) V, that is, during energization of the inductive load 50. Then, the ground potential Vgnd rises according to the internal impedance of the control circuit 11, and accordingly, the control circuit 11 is reset, and the protection circuit control signal Sg1 changes from the H level (5V) to the L level (0V). To do. Then, the transistor Q2 is turned off, and the gate-source voltage Vgs (ΔV3) of the transistor Q3 starts to fall according to the time constant CR of the delay circuit 15.

  Then, at time t1 when the reset detection period K1 of the control circuit 11 has elapsed from time t0, the control circuit 11 cuts off the energization to the inductive load 50. At this time, since the transistor Q1 is kept on by the delay circuit 15, a feedback path can be secured from the power supply line Ls via the freewheeling diode D1, the transistor Q1, the Zener diode ZD1, and the rectifier diode D2. As a result, as described above, the peak value ΔV1p of the drain-source voltage ΔV1 of the semiconductor switch element 12 is limited to be less than the withstand voltage Vmax of the semiconductor switch element 12, and the semiconductor switch element 12 can be prevented from exceeding the withstand voltage (time t1). reference).

  Next, when the capacitor C1 of the delay circuit 15 is discharged, at time t2, when the gate-source voltage Vgs (ΔV3) of the transistor Q3 falls below the on threshold voltage Vth of the transistor Q3, the transistor Q3 is turned off. Transistor Q1 is also turned off. By turning off the transistor Q1, the ground potential Vgnd of the inductive load driving circuit 10 and the control circuit 11 is not determined via the load 50. Therefore, as shown in FIG. 2, the semiconductor switch element 12 is not turned on again after time t2. As a result, as in the case where the cutoff circuit 14 is not provided, the transition to the oscillation state due to the semiconductor switch element 12 being turned on can be prevented.

  That is, when the cutoff circuit 14 is not provided, the ground potential Vgnd of the inductive load driving circuit 10 and the control circuit 11 is determined via the freewheeling diode D1, the transistor Q1, and the load 50. At time t3 when the reset operation period (initialization period) K2 is completed, the semiconductor switch element 12 may be turned on again.

  When the semiconductor switch element 12 is turned on again, ΔV2 (cathode potential of the freewheeling diode D1) rises to 12V. Therefore, the control circuit 11 is reset again as the ground potential Vgnd rises, and the semiconductor switch element 12 is turned off. (See time t4). Thereafter (after time t5), the semiconductor switch element 12 is turned on and off in the same manner, and the inductive load driving circuit 10 may shift to the oscillation state (see the thick broken line).

3. Effects of Embodiment When disconnection of the connection between the ground line Lg and the ground Eth occurs, or when the circuit ground (ground line Lg) of the inductive load driving circuit 10 is floated, the circuit is cut off according to the disconnection or ground floating. The circuit 14 turns off the transistor Q1 (protection switch). Thereby, the potential of the circuit ground, that is, the ground potential Vgnd can be maintained at a high level when the ground is disconnected, the semiconductor switch element 12 is turned on again by the control circuit 11, and further, the semiconductor switch element 12 is turned on / off. That is, it is possible to prevent the oscillation state of the semiconductor switch circuit from occurring. Accordingly, when the connection between the ground line Lg and the ground Eth is disconnected in the inductive load drive circuit 10 including the transistor Q1 (protection switch) that protects the semiconductor switch element 12 when the battery is reversely connected, the semiconductor switch 12 is turned on. Can protect. At this time, the protection transistor Q1 when the battery is reversely connected can also be suitably used to cope with ground disconnection such as floating of the ground.

  Further, when the semiconductor switch element 12 is turned on and the semiconductor switch element 12 is turned on by the reset operation of the control circuit 11 when the semiconductor switch element 12 is turned on, the ON state of the transistor Q1 is maintained by the delay circuit 15 and the feedback path is Secured. A Zener diode ZD1 is provided in the feedback path. Therefore, it is possible to prevent the voltage ΔV1 applied to the semiconductor switch element 12 from exceeding the breakdown voltage of the semiconductor switch element 12 due to the Zener voltage VZD of the Zener diode ZD1. That is, a reverse voltage is generated by the inductive load 50 when the semiconductor switch element is turned off when the semiconductor switch element is off the ground. By turning on the transistor Q1 by the delay circuit 15 at the reverse voltage generation timing, the semiconductor switch The voltage ΔV1 applied to the element 12 can be prevented from exceeding the breakdown voltage by the Zener voltage VZD of the Zener diode ZD1.

  The delay period K3 of the off timing by the delay circuit 15 is set to be shorter than the period K4 from the timing of off-ground (time t0) to the completion timing of reset operation of the control circuit 11 (time t3). For this reason, it is possible to prevent the semiconductor switch element 12 from being turned on again after the reset operation of the control circuit 11 is completed, thereby reliably preventing the semiconductor switch element 12 from oscillating.

  Further, the transistor Q3 (switch circuit) can turn off the transistor Q1 (protection switch) in response to the ground disconnection, and can turn off the transistor Q1 even when the battery Ba is reversely connected. That is, the transistor Q3 allows the transistor Q1 to be used as a protection transistor when the battery is reversely connected and when the ground is disconnected.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.

  (1) In the above embodiment, the example in which the end timing (time t2 in FIG. 2) of the delay period K3 by the delay circuit 15 is set earlier than the completion timing (time t3) of the reset operation is shown. I can't. For example, the end timing of the delay period K3 (time t2 in FIG. 2) may be set later than the reset operation completion timing (time t3).

  In order to reliably recirculate inductive energy via the recirculation path when the ground is off, the time constant CR of the delay circuit 15 is adjusted in accordance with the characteristics (inductance and resistance value) of the inductive load 50. become. Therefore, depending on the characteristics of the inductive load 50, the time constant CR increases, and the time when the gate-source voltage Vgs (ΔV3) falls below the ON threshold voltage Vth of the transistor Q3 is after the time t3 when the reset operation period K2 is completed. It may become. In that case, the semiconductor switch element 12 may be turned on again. For example, after the reset of the control circuit 11 is completed (after time t3), the timing for outputting the protection circuit control signal Sg1 and the drive signal (PWM signal) to the semiconductor switch element 12 is delayed by a predetermined time. I can deal with it.

  That is, even when the transistor Q3 continues to be on after the reset of the control circuit 11 is completed (after time t3) due to the time constant CR, the PWM signal is not output, and the protection circuit control signal Sg1 is If the transistor Q2 is not turned on again without being output, the capacitor C1 of the delay circuit 15 is not charged, and the gate-source voltage Vgs (ΔV3) of the transistor Q3 continues to fall. The transistor Q1 is turned off when ΔV3 falls below the on threshold voltage Vth of the transistor Q3, and the semiconductor switch element 12 is not turned on again thereafter.

  (2) Although the example in which the delay circuit 15 is provided has been described in the above embodiment, the delay circuit 15 may not be provided. Even when the delay circuit 15 is not provided, since the transistor Q1 is turned off when the ground is disconnected, the semiconductor switch element 12 is prevented from being turned on again, and the oscillation state can be avoided.

  (3) In the above embodiment, an example in which the Zener diode ZD1 is provided between the power supply line Ls and the ground line Lg has been described. However, the present invention is not limited to this, and the Zener diode ZD1 may be omitted.

  (4) In the above embodiment, an example in which the delay circuit 15 is configured by a parallel circuit of the capacitor C1 and the resistor R6 has been described, but the present invention is not limited to this. The delay circuit 15 may be constituted by, for example, a digital timer that starts operating upon detection of a ground loss, and the digital timer may delay the off timing of the transistor Q3.

  (5) In the above embodiment, the notification circuit 16 is configured by the light emitting diode LED1 and the N-channel MOSFET (Q4). For example, the light emitting diode LED1 may be a buzzer that emits a warning sound. Furthermore, the notification circuit 16 may be omitted.

  (6) In the above embodiment, the semiconductor switch element 12 and the transistors constituting each switch are not limited to those shown in FIG. For example, the semiconductor switch element 12 may be configured by a bipolar transistor. The transistor Q1 (protection switch) or the like is not limited to a transistor switch.

  (7) In the above embodiment, the configuration in which the transistor Q1 is turned off by the cutoff circuit 14 when the ground is disconnected has been described. However, the present invention is not limited to this. For example, the cutoff circuit 14 is omitted and the gate G of the transistor Q1 is connected to the cathode of the rectifier diode D2 via the resistor R2. Then, as shown in FIG. 1, a Zener diode ZD1 may be provided between the power supply line Ls and the ground line Lg. In this case, although there is a possibility that the inductive load driving circuit 10 oscillates when it is out of ground, the Zener diode ZD1 can prevent the semiconductor switch element 12 from exceeding the breakdown voltage in the oscillating state. Therefore, the semiconductor switch element 12 can be protected when the ground is disconnected.

  (8) In each of the above embodiments, the inductive load driving circuit 10 is mounted on an automobile and the engine cooling FAN driving motor is driven as the inductive load 50. However, the inductive load driving according to the present invention is described. The circuit is adaptable in any case placed between the battery Ba and the inductive load 50.

DESCRIPTION OF SYMBOLS 10 ... Inductive load drive circuit 11 ... Control circuit 12 ... N channel MOSFET (semiconductor switch element)
DESCRIPTION OF SYMBOLS 13 ... Protection circuit 14 ... Cutoff circuit 15 ... Delay circuit 16 ... Notification circuit 50 ... Motor (inductive load)
Ba ... battery C1 ... capacitor (delay circuit)
D1 ... Freewheeling diode ZD1 ... Zener diode LED1 ... Light emitting diode (notification circuit)
R6: Resistance (delay circuit)
Q1 ... N-channel MOSFET (protection switch)
Q2 ... NPN bipolar transistor Q3 ... P-channel MOSFET (switch circuit)
Q4 ... N-channel MOSFET (notification circuit)

Claims (6)

A semiconductor switch element provided between the battery and the inductive load;
A control circuit for controlling switching between energization and non-energization of the inductive load of the semiconductor switch element;
A ground line connected to ground,
A protection circuit connected between the output terminal of the semiconductor switch element and the ground line, and protecting the semiconductor switch element;
A reflux diode;
A protection circuit including a protection switch connected in series to the freewheeling diode and turned off when the battery is reversely connected to prevent a current flow from the battery to the semiconductor switch element via the freewheeling diode,
The inductive load drive circuit, wherein the protection circuit includes a cutoff circuit that turns off the protection switch according to the disconnection when the connection between the ground line and the ground is disconnected. The inductive load drive circuit according to claim 1,
The control circuit has a function of turning off the semiconductor switch element in response to the disconnection,
The cutoff circuit includes a delay circuit that delays an off timing for turning off the protection switch from the timing of the disconnection,
The inductive load driving circuit is
An inductive load driving circuit comprising a Zener diode connected between a power supply line and the ground line. The inductive load driving circuit according to claim 2,
The control circuit has a function of performing a reset operation in response to the disconnection,
The inductive load drive circuit, wherein a delay period of the off timing by the delay circuit is set shorter than a period from the disconnection timing to the reset operation completion timing. In the inductive load driving circuit according to claim 2 or 3,
The cutoff circuit includes a switch circuit that turns off the protection switch in response to the disconnection and turns off the protection switch when the battery is reversely connected,
The inductive load drive circuit, wherein the delay circuit delays a timing at which the protection switch is turned off by the switch circuit. In the inductive load driving circuit according to claim 3 or 4,
The delay circuit is an inductive load driving circuit configured by a parallel circuit of a capacitor and a resistor. In the inductive load driving circuit according to any one of claims 1 to 5,
An inductive load drive circuit comprising a notification circuit that detects the disconnection of the connection between the ground line and the ground and notifies the disconnection.

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