PURPOSE: To enhance the reliability and the maintenance property of a device by smoothing a PWM signal to detect a smoothed current signal and computing the driving current of a motor from the duty ratio of the smoothed current signal and the PWM signal.
CONSTITUTION: A PWM control means 89 controls the driving current of a d. c. motor M in accordance with the duty ratio of a PWM signal PWM1 to a value within a predetermined range about a predetermined standard current. A current detecting circuit 86 detects the value of a current flowing through a resistor Rs and when an abnormal current is detected, an abnormal current signal MS1 is outputted to an abnormal current limiter circuit 88. The current value detected by the current detecting circuit 86 is inputted to a filter (current smoothing circuit) 111 to output a smoothed current signal MD1. A driving current computing means computes the driving current of the d.c. motor from the duty ratio of the smoothed current signal MD1 and the PWM signal PWM1 obtained from the filter 111. Therefore, the reliability and the maintenance property of a motor driver 5 are enhanced.
ADACHI HIDEAKI
NAKAJIMA HIROSHI
KUZUTANI HIDEKI
