PURPOSE:To reduce the number of component parts and a cost, by using a semiconductor electromagnetic-transducer, not only for detecting the magnetic poles of a rotor but also for detecting a temperature. CONSTITUTION:The output voltage of a hole element 22 and reference voltage divided with resistors R2, R3 are applied to an error amplifier 42, and error voltage is applied to a comparator 44, and PWM output signal is fed to a logical circuit 26 via a transistor 48. The output voltage of the Hall element 22 is lowered according to temperature rise, and the output of the error amplifier 42 is increased, and the period of the high pulse duty of the output voltage from the comparator 44 is lengthened. By the period, the output signal of the logical circuit 26 is controlled, and the ON-period of power transistors 28, 30 is lengthened. Average voltage applied to coils 18, 20 is boosted, and the rotational frequency of a motor is increased, and cooling capacity is enhanced.
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