VOLTAGE FED PROGRAMMED START BALLAST

A lighting ballast (10) includes an inverter portion (12) and a resonant portion (14). During a preheat phase, a filament transformer (110) supplies preheat glow currents to lamp cathodes. Also during the preheat phase, the filament transformer boosts the oscillation frequency of the inverter portion (12) to a frequency above a resonant frequency of the resonant portion (14). Once the lamp cathodes are sufficiently heated, the filament transformer (110) is removed from the circuit and the inverter (12) is allowed to start oscillating. A feedback network (150) monitors a high frequency bus (26) and provides input to a shunt regulator (170). The shunt regulator drives the gate of a switch (128) of a bias network (126) and adds or removes the filament transformer (110) to the circuit depending on the conductive state of the switch (128).