JP4412592B2 - State detection circuit for drive circuit - Google Patents

Description

  The present invention relates to a drive circuit state detection circuit particularly suitable for driving a switching element via a pre-drive circuit.

  Conventionally, in a circuit used for electric motor drive control, for example, an FET as a switching element is connected to a power source side or a ground side of the motor, and the motor is controlled by turning on / off the FET. Some of such drive circuits are provided with a circuit for detecting a failure of the FET in order to prevent the failure of the control due to the failure of the FET (see, for example, Patent Document 1).

  An example in which a failure detection circuit is provided in the drive circuit as described above is shown in FIG. In the figure, the motor 1 and the FET 3 in the drive circuit 2 are connected in series between the power supply line V and the ground. The pre-drive circuit 5 that controls the FET 3 is controlled to be turned on / off according to the first transistor TR1 that is turned on / off by H / L of the control output terminal O1 of the CPU 4 and the first transistor TR1. And a pair of second and third transistors TR2 and TR3 connected in series between the power line V and the ground, and between the emitters of the two transistors TR2 and TR3 connected to each other is FET3. Connected to the gate. The drain of the FET 3 is connected to the input terminal I 1 of the CPU 4 through the state detection circuit 6.

In the drive circuit described above, the state of the FET 3 can be detected by the state detection circuit 6. If the voltage is at the power supply (H) level when the FET 3 is turned on, it can be determined that the FET 3 has an open failure. If the voltage is at the ground (L) level when the FET 3 is turned off, the FET 3 has a short failure. Can be judged. When such a failure detection circuit is used in a wiring system for a vehicle as described in Patent Document 1, it is easy to specify an abnormal part, and repair time and labor can be reduced.
JP 2001-309546 A (Page 7, FIG. 1)

  However, even if any of the transistors TR1 to TR3 in the pre-drive circuit has failed, the state detection circuit determines that there is a failure, so there is no problem as a failure determination. There is a problem that it is impossible to determine whether the pre-drive circuit unit is malfunctioning or abnormal. Especially when this failure detection circuit is used in a wiring system for a vehicle, it is necessary to replace all FETs and pre-drive circuits when an abnormality is detected. There is a problem that extra time is required and replacement parts are expensive.

  In order to solve such problems and to identify a failure location in a drive circuit provided with a FET and its control predriver circuit, in the present invention, a switching element connected in series with a load A predrive circuit for driving and controlling the switching element in response to a control signal output from the control means, a switching element state detection circuit connected to a node between the load and the switching element, and the predrive circuit And a pre-drive circuit state detection circuit connected to a node between the switching element and the pre-drive circuit by comparing the detection signals of the switching element state detection circuit and the pre-drive circuit state detection circuit And an abnormality of the switching element is detected.

  As described above, according to the present invention, since the signal output from the pre-drive circuit to the switching element and the signal capable of detecting the state of the switching element are detected and compared with each other, one of the two detection signals is abnormal. If it is detected, it can be determined that an abnormality has occurred in the direction in which the abnormality is detected, so that the failure location can be specified. As a result, it is possible to determine whether the power supply to the switching element should be stopped or whether the predrive circuit should be stopped, and appropriate processing can be performed when a failure occurs, so that damage to the element can be suitably prevented. When there is a need for replacement, only the minimum necessary parts are required.

  In particular, since the switching element state detection circuit is composed of a D / A conversion circuit, determination by, for example, the CPU as the control means can be performed at a voltage level (H / L), and detection can be performed easily. . Further, this is effective for a circuit in which the switching element is an FET and the output of the pre-drive circuit is input to the gate thereof.

  In addition, since the switching element state detection circuit is constituted by a CR filter circuit, when PWM control of the switching element is performed, if an attempt is made to detect a PWM signal, an interrupt is generated according to the pulse frequency, for example, as a control means of the CPU. While the burden may increase and affect other controls, such a burden can be eliminated.

  Further, when the load is an electric motor that opens and closes a vehicle opening / closing body, it is possible to determine which of the switching element that controls the drive of the electric motor and the pre-drive circuit has failed. It becomes possible to control the electric motor that opens and closes the opening / closing body for use.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a principal circuit diagram showing a drive circuit state detection circuit to which the present invention is applied. This state detection circuit is used for a drive control circuit of an opening / closing body such as an auto slide door, a power window, or a sunroof of an automobile. Applicable. The same parts as those of the circuit shown in the background art are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the figure, a relay RY as a main switch is provided between a power supply line V and the motor 1, and a power supply side terminal of the motor 1 is connected to the power supply line V through its contact. A ground side terminal of the motor 1 that opens and closes a vehicle opening / closing body (not shown) is grounded via an FET 3 in the drive circuit 2.

  In the drive circuit 2, there are a CPU 4 as a control means programmed for drive control, a pre-drive circuit 5 that drives and controls the FET 3 in accordance with a control signal output from the first output terminal O1 of the CPU 4, and a CPU 4 2 The detection signal is output to the first input terminal I1 of the CPU 4 connected to the drain of the transistor TR4 for bringing the coil of the relay RY into the excited / de-energized state and the FET3 in accordance with the signal output from the output terminal O2. And a predrive circuit state detection circuit 7 comprising a transistor TR5 provided between the nodes of both transistors TR2 and TR3 of the predrive circuit 5 and the second input terminal I2 of the CPU4. .

  The base of the transistor TR5 is connected to the node of the transistors TR2 · 3, the collector is connected to the constant voltage terminal Vcc, the emitter is grounded, and the collector is connected to the second input terminal I2. As a result, the state of the FET control signal for controlling the FET 3 is detected by the pre-drive circuit 5 and is inverted and input to 2 at the second input terminal.

  The failure detection procedure in the motor drive circuit configured as described above will be described below. First, each waveform in a normal state is shown in FIG. As shown in the upper part of the figure, a PWM signal with a predetermined pulse frequency is output from the first output terminal O1 of the CPU 4, and the gate voltage waveform of the FET 3 becomes the waveform shown in the middle part of the figure accordingly. Since this gate voltage waveform is inverted with respect to the waveform of the first output terminal O1 as shown in the figure, it is inverted and input to the second input terminal I2 via the transistor TR5. The output waveform of the state detection circuit 6 that detects the drain voltage waveform of the FET 3 (the input waveform of the first input terminal I2) is as shown in the lower part of the figure.

  Then, the waveforms input to both input terminals I1 and I2 are compared. The waveform input to the second input terminal I2 is an inverted waveform of the middle waveform in FIG. 2, and is the same as the waveform input to the first input terminal I1 shown in the lower stage of FIG. It can be determined that the circuit is normal.

  Next, a case where at least one of the transistors TR1 to TR3 of the pre-drive circuit 5 has failed will be described below with reference to FIG. As shown in the lower part of FIG. 3, when the drain voltage waveform of the FET 3 does not become a pulse waveform of a predetermined frequency and remains at the L level, either the pre-drive circuit 5 or the FET 3 fails. It can be determined that the FET 3 has a circuit abnormality that is not PWM-controlled. In that case, the gate input signal of the FET 3 is further monitored.

  For example, as shown in the middle part of FIG. 3, when the gate voltage waveform of the FET 3 does not become a pulse waveform of a predetermined frequency and remains at the H level, it can be determined that the pre-drive circuit 5 is abnormal. . In this case, if the pre-drive circuit 5 is turned off (the output of the first output terminal O1 of the CPU 4 is H), the secondary drive of the pre-drive circuit 5 may be induced. In the illustrated example, the relay 1 is turned off and the motor 1 is stopped.

  On the other hand, when the pulse waveform has a predetermined frequency as shown in the middle part of FIG. 4, it can be determined that the pre-drive circuit 5 is normal, and therefore it can be determined that the FET 3 is abnormal. . In this case, the normal pre-drive circuit 5 may be shut off and the power supply of the FET 3 may be shut off. For example, the output of the first output terminal O1 of the CPU 4 is stopped and the motor 1 is stopped.

  In this way, it is possible to cope with an abnormal location, and it is possible to appropriately cope with an abnormality, and it is possible to stop and control an electric motor that opens and closes a vehicle sliding door according to a failure state. The door opening / closing operation unintended by the operator can be prevented. Further, secondary breakdown of the FET 3 and the like can be prevented.

  Next, a second example according to the present invention will be described below with reference to FIG. In addition, about the part similar to FIG. 1 of the said illustration example, the same code | symbol is attached | subjected and the detailed description is abbreviate | omitted. In the second example, a CR filter circuit 7 including a capacitor C1 and a resistor R1 is provided as a pre-drive circuit state detection circuit. As shown in the figure, in order to detect the gate voltage of the FET 3, a capacitor C1 and a resistor R1 are connected in parallel to the nodes of both transistors TR2 · 3, and the node of both transistors TR2 · 3, the capacitor C1 and the resistor R1 are connected. Are connected to the second input terminal I2. As a result, the gate voltage of the FET 3 is input to the second input terminal I2 as a voltage level instead of a pulse frequency.

  When the gate voltage of the FET 3 is detected as it is, the PWM signal is detected, and it becomes a pulse waveform of a predetermined frequency. Therefore, in order to accurately grasp the waveform, it is necessary to perform interrupt processing in accordance with the pulse frequency. is there. Since the PWM signal is usually several tens of kHz, if the CPU 4 performs an interrupt process, the load on the CPU increases, and in the worst case, the interrupt to the second input terminal I2 is unleashed. There is a possibility that the process cannot be performed.

  In contrast, when the PWM signal is processed by the CR filter circuit 7 as described above, the processed signal is within the normal region at the voltage level as shown in the lower part of FIG. It will fit.

  For example, in the case of an open failure of the transistor TR1 of the pre-drive circuit 5, the voltage exceeds the normal region. Therefore, the failure can be determined by detecting whether or not the voltage exceeding the normal region is generated by the CPU 4. Note that even when the PWM carrier frequency becomes extremely slow, it can be detected as an abnormality. In that case, the waveform is 0V output as shown by the broken line in the lower part of FIG. 6, and the abnormality can be determined because it is out of the normal region.

  Also in the second example, it is possible to determine the normality / abnormality of the FET 3 by monitoring the waveform to the input terminal I1 in the same manner as described above.

  It goes without saying that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. For example, in the present embodiment, the case where the drive circuit state detection circuit is applied to a control circuit for a vehicle opening / closing body is shown, but the present invention is not limited to this, and a control circuit that drives and controls a load. Applicable if available.

It is a principal part circuit diagram which shows the state detection circuit for drive circuits to which this invention was applied. It is a figure which shows the waveform at the time of normal. It is a wave form diagram at the time of abnormality of a predrive circuit. It is a wave form diagram at the time of abnormality of FET. It is a figure corresponding to FIG. 1 which shows a 2nd example. It is a figure which shows the waveform at the time of normal in a 2nd example. It is a wave form chart at the time of abnormality of the predrive circuit in a 2nd example. It is a principal part circuit diagram which provided the conventional state detection circuit.

Explanation of symbols

1 Motor 2 Drive circuit 3 FET
4 CPU
5 Pre-drive circuit 6 State detection circuit 7 Pre-drive circuit state detection circuit 8 CR filter circuit

Claims (5)

A switching element connected in series to the load, a pre-drive circuit for driving and controlling the switching element in accordance with a control signal output from the control means, and a switching connected to a node between the load and the switching element An element state detection circuit, and a predrive circuit state detection circuit connected to a node between the predrive circuit and the switching element,
The switching element state detection circuit detects an abnormality in the circuit, and when an abnormality is detected in the circuit, the detection signals of the pre-drive circuit state detection circuit and the switching element state detection circuit are compared with each other. A drive circuit state detection circuit for detecting whether or not the pre-drive circuit is abnormal.   2. The drive circuit state detection circuit according to claim 1, wherein the switching element state detection circuit comprises a D / A conversion circuit.   The drive circuit state detection circuit according to claim 1, wherein the switching element is an FET, and an output of the pre-drive circuit is input to a gate thereof.   4. The drive circuit state detection circuit according to claim 1, wherein the switching element state detection circuit comprises a CR filter circuit. The drive circuit state detection circuit according to any one of claims 1 to 4, wherein the load is an electric motor that opens and closes a vehicle opening / closing body.

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