Pulse width modulation motor driving device for controlling driving operation of a three-phase motor at the start and ordinary rotational frequency

摘要

A PWM duty ratio control signal having pulses set to a frequency higher than an audio frequency range and set to a fixed duty ratio is produced in a PWM duty ratio control signal producing unit. In a PWM control unit, when a rotational frequency of a motor is lower than a prescribed rotational frequency, a time period ratio of a charging operation to a discharging operation for the motor is determined according to the fixed duty ratio of the PWM duty ratio control signal. The rotational frequency of the motor lower than the prescribed rotational frequency denotes that a driving operation of the motor is just started. A driving unit drives the motor to alternately perform the charging operation and the discharging operation of the motor with the time period ratio.