Circuit arrangement for powering a two-phase asynchronous motor

Abstract

A power supply circuit for a two-phase asynchronous motor having two windings at a preset angle there-between. The supply circuit has three nodes at which are respectively supplied three node voltages U1, U2, U3 which are derived as logic combinations of a basic pulse train and a pulsed switching signal having a switching frequency and a duty cycle. The motor windings are respectively connected between the first and second nodes and between the second and third nodes. The voltage U2 at the second node has a rectangular waveform. The voltages U1 and U3 at the first and third nodes alternate between time intervals in which the voltage level is constant and time intervals in which the voltage is pulse modulated, and have a phase angle there-between corresponding to that between the motor windings. Pulse modulated intervals of each of the first and third node voltages coincide with constant voltage intervals of the other of those voltages, and the pulses in the pulse modulated intervals have a duty cycle which corresponds with a desired amplitude ratio of the voltages produced across the motor windings. The circuit achieves significant reduction in the required number of switching edges of the node voltages, thereby reducing power dissipation.