JP2012085382A - Overcurrent protection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overcurrent protection apparatus that can diagnose a failure in a semiconductor switch element while keeping energized a current path in which the semiconductor switch element is used as a fuse.SOLUTION: The overcurrent protection apparatus that has a transistor 21 and a protection circuit 30 for driving the transistor 21 and turns off the transistor 21 via the protection circuit 30 to prevent an overcurrent from flowing through a power line 13 includes: a dropper regulator 20 capable of using the transistor 21 as a variable resistor to output a voltage lower than an input voltage Vin to the transistor 21 as an output voltage Vout of the transistor 21; and a control circuit 40 for detecting a failure in the transistor 21 on the basis of the output voltage Vout during operation of the dropper regulator 20.

Description

  The present invention includes an overcurrent protection device that includes a semiconductor switch element and a drive unit that drives the semiconductor switch element, and prevents an overcurrent from flowing in a current path when the semiconductor switch element is turned off by the drive unit. About.

  As a conventional technique, a vehicle power supply system using a semiconductor switch element as a fuse is known (for example, see Patent Document 1).

JP 2005-253125 A

  However, when a semiconductor switch element is used as a fuse in a current path that always requires energization, the semiconductor switch element cannot be easily turned off in order to diagnose a failure of the semiconductor switch element.

  Accordingly, an object of the present invention is to provide an overcurrent protection device that enables failure diagnosis of a semiconductor switch element while energizing a current path in which the semiconductor switch element is used as a fuse.

In order to achieve the above object, an overcurrent protection device according to the present invention comprises:
A semiconductor switch element;
Driving means for driving the semiconductor switch element,
An overcurrent protection device that prevents an overcurrent from flowing in a current path by turning off the semiconductor switch element by the driving means,
A dropper regulator capable of outputting a voltage lower than an input voltage of the semiconductor switch element as an output voltage of the semiconductor switch element by using the semiconductor switch element as a variable resistor;
And an abnormality detecting means for detecting an abnormality of the semiconductor switch element based on the output voltage when the dropper regulator is operated.

  According to the present invention, it is possible to diagnose a failure of a semiconductor switch element while energizing a current path in which the semiconductor switch element is used as a fuse.

It is a lineblock diagram of overcurrent protection device 1 which is one embodiment of the present invention. It is the figure which showed the transition of the output voltage Vout when the transistor 21 is normal. 3 is a flowchart illustrating a first operation example of the overcurrent protection device 1. 5 is a flowchart showing a second operation example of the overcurrent protection device 1. 5 is a flowchart showing a third operation example of the overcurrent protection device 1.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an overcurrent protection device 1 according to an embodiment of the present invention. The overcurrent protection device 1 includes a transistor 21 that is used as a semiconductor fuse and a protection circuit 30 that drives the transistor 21. When the transistor 21 is turned off by the protection circuit 30, the overcurrent flows to the power supply line 13. It is to prevent.

  The transistor 21 is an example of a semiconductor switch element. Although FIG. 1 shows a configuration using a P-channel MOSFET as the transistor 21, other types of semiconductor switch elements may be used. Other types of semiconductor switching elements include N-channel MOSFETs, PNP or NPN bipolar transistors, IGBTs, and the like.

  The transistor 21 is provided between the power supply 11 and the load 12 and is inserted on the power supply line 13 that connects the power supply 11 and the load 12. The power supply line 13 is a current path through which a current to be supplied from the power supply 11 to the load 12 flows. An input voltage Vin supplied from the power supply 11 is input to the source of the transistor 21, and an output voltage Vout applied to the load 12 is output from the source of the transistor 21. In a normal state where the transistor 21 is on in the saturation region, the input voltage Vin and the output voltage Vout are substantially equal.

  The power source 11 is a direct current power source, and specific examples thereof include a generator such as a battery and an alternator. Specific examples of the load 12 include a computer such as an ECU (electronic control unit), a drive unit that drives an electric load such as a sensor, a motor, a lamp, a solenoid, and a motor.

  The protection circuit 30 is a driving unit that drives the transistor 21. The protection circuit 30 outputs a drive signal Va for turning off the transistor 21 to the gate of the transistor 21 by detecting that the current flowing through the power supply line 13 exceeds a predetermined reference current value. When the transistor 21 is turned off, an overcurrent can be prevented from flowing through the power supply line 13.

  The overcurrent protection device 1 includes a dropper regulator 20 that uses the transistor 21 as a variable resistor, and a control circuit 40.

  The dropper regulator 20 is a step-down circuit that can output a constant voltage Vd lower than the value of the input voltage Vin of the transistor 21 from the drain of the transistor 21 as the output voltage Vout by using the transistor 21 as a variable resistor.

  The dropper regulator 20 includes a transistor 21, a detection circuit (22, 23) that outputs a detection voltage Vb corresponding to the voltage value of the output voltage Vout of the transistor 21, and the detection voltage Vb is input to an inverting input terminal and a reference voltage This is a circuit comprising an operational amplifier 25 in which Vref is input to a non-inverting input terminal, and a capacitor 24 inserted between the output terminal and the inverting input terminal of the operational amplifier 25. The detection circuit (22, 23) outputs a voltage obtained by dividing the output voltage Vout by the resistors 22 and 23 as the detection voltage Vb.

  Therefore, according to this configuration, when the output voltage Vc of the operational amplifier 25 is applied to the gate of the transistor 21, negative feedback is applied to the output voltage Vout, so that the output voltage Vout is lower than the value of the input voltage Vin. Regulated to a constant voltage Vd. The constant voltage Vd may be set to a value larger than the minimum operating voltage necessary for normal operation of the load 12 by adjusting the constants and the like of each element in the dropper regulator 20. For example, when the input voltage Vin supplied from the power supply 11 is 12V or more, the constant voltage Vd may be set to 11V.

  The control circuit 40 is an abnormality detection unit that detects an abnormality of the transistor 21 based on the value of the output voltage Vout when the dropper regulator 20 is operated. The control circuit 40 includes, for example, an operation command circuit that outputs an operation command signal for operating the dropper regulator 20, a detection circuit that detects the output voltage Vout, and an abnormality determination that determines an abnormality of the transistor 21 based on the detection result of the output voltage Vout. The circuit includes a communication circuit that transmits a determination result of whether or not the transistor 21 is abnormal to another device. Some or all of these circuits can be realized by, for example, a microcomputer.

  For example, the control circuit 40 turns on the switch 52 for turning on / off the signal path between the gate of the transistor 21 and the output terminal of the operational amplifier 25, whereby the step-down function of the dropper regulator 20 works, and the dropper regulator 20 can be stepped down. As shown in FIG. 2, the control circuit 40 operates the dropper regulator 20 for a short time to detect whether or not the output voltage Vout is regulated to a predetermined constant voltage Vd, and the output voltage Vout is constant. When the voltage Vd is not regulated, it is determined that the transistor 21 is abnormal.

  FIG. 2 is a diagram showing a transition of the output voltage Vout when the transistor 21 is normal. If the transistor 21 is normal, the output voltage Vout is regulated to the constant voltage Vd while the dropper regulator 20 is operating. If the transistor 21 is abnormal, the output voltage Vout is output even if the dropper regulator 20 is operated. The voltage Vout is not regulated to the constant voltage Vd. For example, when the transistor 21 is on and has a failure that does not switch off, the output voltage Vout does not drop to the constant voltage Vd. Therefore, the control circuit 40 determines that the transistor 21 is abnormal if the output voltage Vout does not drop to the constant voltage Vd during the period (inspection section Ta) during which the dropper regulator 20 is operated. The inspection section Ta is preferably a short time in consideration of heat generation of the transistor 21, and is preferably 100 ms or less, for example.

  As shown in FIG. 1, the control circuit 40 controls on / off of the switch 51 for turning on / off the signal path between the gate of the transistor 21 and the protection circuit 30 that outputs the drive signal Va. To do. The protection circuit 30 can turn on / off the transistor 21 when the switch 51 is switched to the on side by the control circuit 40. However, when the switch 51 is switched to the off side by the control circuit 40, the protection circuit 30 21 cannot be turned on / off.

  FIG. 3 is a flowchart showing a first operation example of the overcurrent protection device 1. The control circuit 40 monitors a predetermined input signal input to the control circuit 40 (step S14), and whether or not the monitoring result corresponds to a diagnosis start condition predetermined as an execution condition for the failure diagnosis of the transistor 21. Is determined (step S16). For example, the control circuit 40 monitors the starter signal or monitors the power supply that is activated when the engine is started, thereby performing failure diagnosis based on the diagnosis start condition until the predetermined time elapses from the engine start time. Conduct in between.

  When the monitoring result corresponds to the diagnosis start condition, the control circuit 40 operates the dropper regulator 20 by turning on the switch 52 in FIG. 1 (step S18). Then, the control circuit 40 detects whether or not the output voltage Vout during the operation of the dropper regulator 20 is regulated to the constant voltage Vd (step S20), and if it is regulated within a predetermined range, the transistor 21 Is determined to be normal, and if not regulated within a predetermined range, the transistor 21 is determined to be abnormal. When the control circuit 40 determines that the transistor 21 is abnormal, the control circuit 40 notifies the other control device of the result of determining that the transistor 21 is abnormal as a failure diagnosis result of the transistor 21 (step S22). The other control device executes a predetermined control operation according to the abnormality determination result of the transistor 21. For example, by performing a warning operation to the user by a lamp display or the like, it is possible to notify the user of the abnormality of the transistor 21 and prompt the user to replace it.

  FIG. 4 is a flowchart showing a second operation example of the overcurrent protection device 1. The description of the same parts as in FIG. 3 is omitted. Before detecting the output voltage Vout, the control circuit 40 detects the state of the vehicle by communication or the like (step S10), and based on the detection result, whether the current vehicle state is a state in which the voltage fluctuation of the power source 11 is small. It is determined whether or not (step S12). When the control circuit 40 determines that the voltage fluctuation of the power source 11 is small, the control circuit 40 performs failure diagnosis of the transistor 21 (step S14 and subsequent steps). Accordingly, since the failure diagnosis of the transistor 21 can be performed based on the detection result of the stable output voltage Vout, the accuracy of the diagnosis result can be increased.

  Examples of the vehicle state detected in step S10 include a power generation state of an alternator. The control circuit 40 can determine whether or not the input voltage Vin supplied from the vehicle power supply 11 is stable by detecting the power generation state of the alternator. Moreover, the running state of a vehicle is mentioned as a state of the vehicle detected by step S10. For example, if it is detected that the vehicle is in a stopped state, the control circuit 40 can determine that the vehicle state at that time is a state in which the voltage fluctuation of the power supply 11 is small.

  FIG. 5 is a flowchart showing a third operation example of the overcurrent protection device 1. The description of the same parts as in FIG. 3 is omitted. Before detecting the output voltage Vout, the control circuit 40 notifies other devices that a failure diagnosis is being performed via a communication line such as CAN (step S17). As a result, the other device that has received the fact that the failure diagnosis is being performed can shift to the operation mode in which the voltage fluctuation of the power supply 11 is suppressed, so that the input voltage Vin supplied from the power supply 11 is stable. In this state, the dropper regulator 20 can be operated to perform failure diagnosis based on the stable output voltage Vout. As a result, the failure diagnosis accuracy of the transistor 21 can be increased.

  Thus, according to the above-described embodiment, since the transistor 21 does not reach the cutoff region from the saturation region by the operation of the dropper regulator 20 (that is, the transistor 21 is not turned off), the transistor 21 is used as a semiconductor fuse. The failure diagnosis of the transistor 21 can be performed while the power supply line 13 is energized.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

  For example, the operation time of the dropper regulator 20 (that is, the inspection section Ta shown in FIG. 2) may be a period from when the engine is started to when a predetermined time elapses, or when the engine is operating or stopped. It may be an arbitrary period. The operation of the dropper regulator 20 is not limited to being performed only once while the engine is operating or stopped, but may be performed intermittently.

  In FIG. 1, the switch 52 may be switched from off to on after the switch 51 is switched from on to off depending on the circuit configuration of the protection circuit 30, or the switch 52 may be switched off while the switch 51 remains on. It may be switched on.

DESCRIPTION OF SYMBOLS 1 Overcurrent protective device 13 Power supply line 20 Dropper regulator 21 Transistor 30 Protection circuit 40 Control circuit

Claims (1)

A semiconductor switch element;
Driving means for driving the semiconductor switch element,
An overcurrent protection device that prevents an overcurrent from flowing in a current path by turning off the semiconductor switch element by the driving means,
A dropper regulator capable of outputting a voltage lower than an input voltage of the semiconductor switch element as an output voltage of the semiconductor switch element by using the semiconductor switch element as a variable resistor;
An overcurrent protection device comprising: an abnormality detection means for detecting an abnormality of the semiconductor switch element based on the output voltage when the dropper regulator is operated.

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