| 摘要 |
PROBLEM TO BE SOLVED: To detect a current that flows in a motor with high accuracy using a simple circuit structure. SOLUTION: When a motor 9 stops, a fail-safe driving signal FS turns off a relay 29 to break a power source voltage VB. When the motor 9 operates, the signal FS turns on the relay 29 to supply power to a driver 22 and also turns on transistors 34, 36 to supply the voltage VB. The voltage to the transistor 35 is divided by resistors 43, 44 and is turned on by a voltage delayed by the time constant of the resistor 43 and a capacitor 38 to output a detection signal. This detection signal causes a microcomputer 15 to output a driving signal to a pre-driver 20. The resistance of the resistors 43, 44 are set, in such a way as to turn on the transistor 35, if the delayed voltage is hither than the minimum operating voltage of a motor current sensor 24. As the delay time, a time is set that is required, until the operation of the sensor 24 becomes stable after the supply of the power source voltage VB.
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