An electronic ballast with inductively coupled preheating circuits

This paper presents an electronic ballast with inductively coupled preheating circuits based on a half-bridge series-resonant parallel loaded inverter. A ballast with the circuits can ignite lamps at low temperature (-30/spl deg/C), while still keeping filaments properly preheated. This can save energy for nondimmable ballasts by reducing the filament voltage and can increase lamp life by reducing voltage stress imposed on lamps during start-up transition. Moreover the proposed preheating circuits can be readily modified to fit to other types of lamps by adjusting the turns ratio of the coupled inductors and/or the capacitance of their series capacitors. Hardware measurements have verified that 20000 on-off tests (25-second on and 35-second off) for PLT 42 W lamps have been conducted without observing significant sputtering.