Abstract: A control circuit comprises a TRIAC (T) in series with the stator winding (1) of the motor across the terminals of an alternating voltage source (V.sub.M). A fixed sensor (H) is associated with the rotor (R) and operable to provide a signal indicative of the magnetic polarity of the part of the rotor (R) facing it. A diode circuit (DC) including at least one Zener diode supplies the sensor (H) and provides a signal indicative of the polarity of the alternating supply voltage (V.sub.M). A driver circuit (PC) is connected to the sensor (H) and to the diode circuit (DC) and pilots the control input (g) of the TRIAC (T) in a predetermined manner in dependence on the instantaneous position of the rotor (R) and the polarity of the supply voltage (V.sub.M).