DC Motor soft-start circuit

Claim 1

A DC motor driving circuit comprising: a motor having polyphase exciting coils; a DC power supply; an excitation current supply line for supplying excitation current from the DC power supply to the polyphase exciting coils; exciting coil switching means connected to the excitation current supply line and the polyphase exciting coils, for sequentially switching the polyphase exciting coils; excitation current control means for controlling the magnitude of the excitation currents to be supplied to the exciting coils; and timing signal producing means for producing a timing signal which, when the motor is started, is supplied to the excitation current control means so as to suppress the magnitude of the excitation current, said timing signal producing means including a start switch adapted to be turned ON when the motor is started; a time constant circuit for producing a signal which is lowered from a predetermined level to a ground level during a predetermined period of time following the turning on of the start switch; a triangular wave producing circuit; and a comparator connected to receive an output signal of the time constant circuit and an output signal of the triangular wave producing circuit and supply pulses which successively decrease in their widths, to the excitation current control means.