Closed loop rotational speed control system having means for generating a PNM signal for an electric motor

摘要

A PNM (pulse number modulation) signal is generated in response to a DC signal the magnitude of which is in proportion to the detected rotational speed of an electric motor to regulate a period of time for which an electric power is fed to the motor by switching the electric power in accordance with the PNM signal. The switching frequency is arranged to vary depending on the variation of the load of the motor.