Control circuit for an A.C. motor

A control circuit for an A.C. motor with at least two sets of windings, and having a device controlling the power supply to the windings, comprising:

• a dividing circuit with a counter connected to a source of voltage through a voltage-controlled oscillator and transmitting a bit pattern corresponding to the instantaneous phase of the voltage of said source, the bit pattern corresponding to the maximum counting corresponds to 90.degree., binary comparator units receiving the bit pattern through a data bus for comparison with both a preselected phase in the form of a bit pattern and a bit pattern corresponding to a phase symmetrical with respect to the maximum value of the voltage, control means and trigger circuit therefor, said second bit pattern being the complement to the preselected bit pattern, each comparator unit at bit pattern identity transmitting a signal for said trigger circuit for said control means, said control means controlling power supply for individual windings, and a switch-off circuit, one of said control means stopping the power supply to a winding before the zero cross-over of the voltage of said source by said switch-off circuit.