Abstract: The invention relates to a protective circuit for an inverter having semiconductor control elements. The protective circuit includes a series regulator in its inlet branch and an intermediate filter circuit with the capacitor thereof extending between the inlet and outlet branches. First and second signal generators control the series regulator and the inverter. A control unit controls the first signal generator for normal operation. Parallel comparator units have monitoring inputs connected to different parts of the protective circuit for detecting abnormal conditions and outputs connected to both of the signal generators to effect the immediate turning off of the series regulator and the inverter when abnormal conditions are sensed. The inverter is off concurrently with the comparator output signal but a multivibrator switch having a predetermined period causes the series regulator to be off during that whole period independently of the comparator output signal.

Abstract: The invention relates to a control circuit for a self-starting electric motor of the type having stator windings in respective series relation with gate type electronic switches which are controlled by control impulses generated in a gate circuit. A motor starting pulse generator is connected to the gate circuit which generates short starting pulses and long blocking pulses. Motor operating controls responsive to commutation impulses are connected to the gate circuit which override the effects of the motor starting pulse generator during normal operation. An integrator for the commutation pulses generates a voltage level signal which corresponds to the speed of the motor. A comparator compares this signal with a reference voltage and, when the signal reaches a predetermined level, the motor starting generator is overriden. When the motor is stopped for any reason the short starting pulses attempt to start the motor at intervals determined by the length of the blocking signals.