| 摘要 |
PURPOSE:To prevent an accident such as an abnormal heating of a power transistor or a motor by setting the power transistor for controlling the motor current upon detection of the motor shortcircuit state to shut-off state, thereby preventing the excessively abnormal current from flowing to the motor. CONSTITUTION:When a motor becomes in a shortcircuit state, the collector voltage of a power transistor 10 abruptly decreases, no current is supplied to the base of a detecting transistor 11, which thus bemcomes in shut-off state, with the result that the base current of the transistor 10 does not flow out. Thus, the transistor 10 becomes in shut-off state, its collector current is shut off, the voltage drop due to a bridge resistor 2 decreases, and the contactor voltage decreases. Accordingly, the transistor 11 further becomes in shut-off state. In this manner, the transistor 11 detects the motor shortcircuit state, thereby shutting off the transistor 10 and preventing the excessively abnormal current from flowing to the motor 1. |
