| 摘要 |
PURPOSE:To realize the stable PWM control for the rotating speed of a DC motor without the allophone and waviness of the motor and to suppress the heating of a transistor when a duty ratio is large. CONSTITUTION:An average voltage value, which is applied on a DC motor 20, is detected. The PWM control of the applied voltage for the DC motor is performed so that the deviation between the average voltage value and a speed command value is decreased. The average voltage value corresponding to the duty ratio of 90% is made to be a boundary, and the triangular waves having the different frequencies from a triangularwave generating circuit 4 are switched with a judging circuit 17. Namely, when the value is 1 smaller than the duty ratio of 90%, a rectangular wave of 20kHz is used. When the value becomes larger, a rectangular waves of 1kHz and 20kHz, which is fixed to the duty ratio of 90%, are used. Thus, the PWM signal is synthesized. In this way, the heating of a transistor when the duty ratio is large can be suppressed, and the allophone and waviness of the motor can be made hard to feel regardless of the magnitude of the duty ratio. |
