Dc/ac bridge circuit

Abstract

In full or half DC/AC bridge circuits, the current through the control circuit, by which the power transistors T1,T2 are switched, is derived from the high supply voltage via a resistor. In order to reduce this current and the dissipation associated therewith, the control circuit includes an additional switch, preferably a MOST T4, which is non-conducting when the inverter transistor T3 is conducting and which is conducting when the transistor T3 is non-conducting. The control circuit thus becomes practically currentless. When the control electrode is applied to a suitable voltage, the transistor T4 can be controlled by its source voltage and thus becomes self-controlling. Thus, the circuit can be kept simple. The bridge circuit is particularly suitable for use with gas discharge lamps.