International Business Machines Corporation

Brian P Fenton

John G Ramage

Robert Duncan Commander

John C Davy

A power switching circuit for switching power repetitively to a load at a relatively low frequency employs a power switching device which is driven across an isolating transformer interface. The drive signals are high frequency pulse signals which are modulated with the low frequency switching information, the modulations being detected in the secondary circuit of the transformer. Such an arrangement affords isolated driving with fast switching edges and requires only a small transformer. Power for the detection circuit is derived by rectification of the high frequency signals induced in the transformer secondary.

Transformer coupled power switching circuit

A single phase induction motor control system employs power line assisted starting and runs at higher than power line frequency from an electronically generated inverter supply. This inverter supply is employed to provide an out of phase mains frequency signal to the run winding during starting in order to create the rotating magnetic field needed to start the motor. After the motor has started, the power line supply is disconnected from the start winding and the inverter supply frequency is increased gradually to a final value corresponding to the desired operating speed. In this system no phase shifting capacitors are needed to provide the out of phase starting voltage and the run winding is optimized for running conditions.

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Totton, United Kingdom

Brian P Fenton