Patent ID: 6854299

Claim:
A rotary speed control device of a universal motor pulsatingly fed from an a.c. mains having a half-period and a voltage minimum value, the control device comprising: a full-wave rectifier connected between the a.c. mains and the motor, said rectifier having an output; an electronic switch connected in series with the motor and said rectifier, said electronic switch being periodically driven in dependence on the mains half-period by: switching on the switch prior to the main minimum voltage value at a first instant in time variably set in accordance with a rotary speed of the motor to be set; and switching off the switch at a second instant in time shortly after the respective minimum voltage value; and a free-wheeling diode connected in parallel with the motor and non-conducting for a polarity at said output of said rectifier, for assuring a substantially gap-free current flow through the motor.