A new heating concept for fluorescent lamp ballasts

A filament-heating concept for dimmable and nondimmable electronic ballasts has been developed. The filaments are supplied by an additional heating transformer, which is connected to the half bridge and controlled by a bi-directional transistor-set. This makes it easy to save energy by cutting off the heating-current in the normal operation mode for nondimmable ballasts. It is possible to adjust the value of the filament voltage with the duty-cycle of the heating transistor-set. This feature is useful for "multi-lamp-ballasts" which supply lamps with different electrical characteristics.