| 摘要 |
PURPOSE:To suppress the switching loss of a power transistor by lowering the carrier frequency of a pulse width modulation proportionally to the increase in the load current of a motor. CONSTITUTION:An error amplifier 21 outputs an error voltage between the speed voltage Vf outputted from a speed detector 17 and the speed command voltage Vs. A comparator 24 compares a triangular carrier signal from a variable frequency oscillator 22 with the error signal and supples a pulse width modulation signal to a power transistor 16. The frequency of the triangular carrier signal from the oscillator 22 decreases when the load current to a DC motor 2 increases. Thus, the switching loss of the power transistor can be suppressed. |
