Starting circuit for push-pull chopper with unijunction transistor - applies RC circuit start signal to single auxiliary winding on chopper transformer

摘要

The starting circuit, for a push-pull chopper, starts the chopper oscillating even with slowly rising voltages and therefore requires no second auxiliary winding. The chopper contains a transformer with a feedback winding and a single auxiliary winding that applies the starting signal to the chopper transistors. The d.c. supply is voltage stabilised and applied via an RC circuit to a unijunction transistor. The transistor produces the starting signal which is amplified and applied to the auxiliary winding. After the chopper has begun to oscillate, a rectangular waveform is induced in the auxiliary winding. This waveform is rectified and applied to a transistor which short circuits the RC circuit's capacitor -- the starting signal then stops.