Lamp driver circuit

Abstract

A lamp driver circuit is presented herein for driving a lamp circuit with an AC squarewave voltage at a relatively high frequency. The driver circuit includes a self-oscillating half-bridge circuit having a pair of input terminals connected across a DC voltage supply, which may be obtained from rectifying an AC voltage signal, and a pair of output terminals connected across a lamp circuit including a lamp, either a resistive lamp or a gaseous discharge lamp, to be energized. The circuit also includes a pair of capacitors connected together in series across the input terminals and having a junction therebetween connected to a first one of the output terminals. The bridge circuit also includes first and second switching transistors connected together in series across the input terminals. A transformer is provided having first and second windings thereon respectively connected to the first and second switching transistors for alternately applying forward biasing base drive current to the first and second transistors. A third winding on the transformer is connected in series from the junction of the two transistors to a second one of the output terminals for purposes of supplying a squarewave voltage across the output terminals for driving the lamp circuit. A starter circuit serves to start the half-bridge circuit by initially turning on one of the switching transistors in such a manner that while one transistor is being forward biased into conduction, the other transistor is reverse biased.