Abstract: A forward converter circuit (FIG. 1) is provided with a transformer reset sensing circuit (FIG. 2) whereby base drive to the switching transistor TR1 is inhibited until after reset of the transformer T1. The reset sensing circuit includes a sensing winding T1d provided on the transformer for sensing the waveform at the primary winding T1a, a comparator IC1 and diodes D5, D4 connected in such a way that one input of the comparator is high when the waveform changes in one direction, and the other input of the comparator is high when the waveform changes in the other direction. The output of the comparator inhibits switching of the transistor before reset and thus allows the use of a maximum switching duty cycle of 50% without risk of transformer saturation.

Abstract: Power supply apparatus is disclosed including an inverter, such as a half-bridge inverter, and control means for controlling the frequency of operation of the inverter. The control means includes a further control winding on the transformer of the invertor, and means for applying a short circuit of one or other or both polarities to the control winding in order to activate a switching transition of the inverter. In one embodiment, the control means is used to fix the frequency of operation of a free-running inverter; in another embodiment, short circuits of both polarities are applied to the control winding for an overlap period in order to provide a "dwell" period between switch-off of one inverter transistor and switch-on of the other, this method of operation providing pulse width modulation control of the output waveform of the inverter.

Abstract: Voltage converter apparatus is disclosed having circuitry for regulating the output voltage to maintain it at a regulated value. Use is made of switching devices that switch between their alternative states in a cyclic manner and at a particular frequency which is determined by the circuit constants. An inductance is provided for modifying the waveform of the current fed to the output transformer, so that at certain periods of the cycle there is a lesser contribution to the integrated output--i.e., the output is not a true 1:1 square wave. Then, by changing the switching intervals, the integrated output can be controlled. A current transformer is provided for sensing current changes occurring in the output transformer, and a short circuit arrangement is provided for short circuiting a control winding of the converting transformer to control the instants of switching of the switching devices.