Speed control apparatus for a motor

摘要

A speed control apparatus for a motor, wherein the counter-electromotive voltage is detected with great precision even when the counter-electromotive voltage to be caused from the motor driving coils is small or the ambient temperature is changed. The voltages corresponding to the detection voltages are turned into speed signals. The emitter resistance of the driving transistor, which is the cause of the torque reduction, can be removed, and uneven rotation, uneven torque is reduced. The speed control apparatus provides a composite voltage of driving coil voltages that are converted by an inversion amplifier. The voltage corresponding to the composite voltage provides the speed signal. This voltage is transferred to the driving coils and precise speed control is produced without a reduction in the controllable maximum torque or the starting torque.