Abstract: A variable burst length, switching system for controlling speed and direction of rotation of a two phase AC motor is disclosed. A bipolar DC command or error signal is supplied to a pair of pulse width modulators, one of which, depending on the DC signal polarity, produces a first pulse train of which the ratio of pulse duration to pulse repetition interval or average value is indicative of the required motor speed. The first pulse train is supplied to synchronization means which generates a second substantially identical pulse train wherein the leading and trailing edges of the pulses are timed to occur in a fixed time relationship with the energization voltage for the motor. The second pulse train comprises the input signal to current control means which is operable to energize the motor.