Abstract: A control circuit for operating a synchronous motor with a polyphase armature winding in a d-c voltage network comprises a switch device for successively connecting the winding phases with the network, a switch signal generator which produces switch signals for the switch device, a logical stage for logically loading the switch devices with said signals. The circuit also includes a voltage/frequency converter, a starting device and a re-starting device. The converter generates a pulse succession which is increased by the starting member from zero to a predetermined value to re-start the motor when its current exceeds a predetermined value.