A novel parallel-resonant programmed start electronic ballast

A novel programmed start electronic ballast based on a current-fed push-pull parallel-resonant inverter is described. The ballast produces essentially zero open-circuit voltage during the preheating interval. The filament preheating voltages are produced by windings that are coupled to the DC choke of the parallel-resonant inverter. During preheating, the two switching transistors of the parallel-resonant inverter are inhibited while a third switching transistor develops a square-wave voltage across the DC choke. At the end of the preheating interval, the third switching transistor is inhibited, and normal sinusoidal oscillation commences in the parallel-resonant inverter.