High-frequency oscillator-inverter ballast circuit for discharge lamps

摘要

A current fed high frequency oscillator-inverter ballast circuit includes a parallel resonant tank circuit for driving a pair of series connected discharge lamps via a series ballast capacitor. A regenerative power supply switches on when a fluctuating main DC supply voltage drops below a given level thereby providing a constant level auxiliary DC supply voltage to the oscillator inverter to maintain oscillation and lamp operation. When the main DC supply voltage exceeds said given level, the regenerative power supply switches out. The oscillation frequency is f2 during operation of the main supply and automatically switches to a frequency f1 when the regenerative power supply takes over. The frequency shift is automatic during each half cycle of a 60 Hz AC supply and is in a direction so as to maintain lamp current relatively constant. A novel high frequency leakage transformer may be provided to couple the high frequency inverter to the discharge lamp load to provide both a current limiting (ballast) action and automatic control of the lamp heater current to maintain high efficiency operation.