PURPOSE: To guarantee the safety of a motor drive itself by coupling latch means with set and reset terminals utilizing the output of an oscillator as a reset signal to motor current limiting means, calculating a logic product of the output and the output of a comparator for determining the duty of a motor winding, and coupling it to a power amplifier.

CONSTITUTION: A motor current is detected and amplified by a current detector 5. When the voltage arrives at a preset current limiting level VCL, the output of a current limiting comparator 6 is switched as b. In this case, a RS type flip-flop 10 is set by the output of the current limiting comparator 6, a power amplifier 1 is cut OFF as shown in Fig. 2c through an AND gate 8, and the motor current is reduced. Since the oscillation frequency of an oscillator 4 is set to approx. 10-100kHz to become much higher frequency than a time constant of the inductance component Lm and the resistance component Rm of the motor, the period of the operation of limiting the current the release thereof becomes the same as the oscillation frequency of the oscillator 4.