ELECTRONIC BALLAST FOR A GAS DISCHARGE LAMP WITH CONTROLLED FILAMENT HEATING DURING DIMMING

摘要

An electronic ballast has control circuitry to operate a gas discharge lamp in both full and dimmed illumination modes. A dimming controller serves as the mechanism to permit a selection between full and dimmed illumination modes. The dimming controller signal has a dimming request range which describes the range of dimming controller signal magnitudes. The electronic ballast also includes a full power circuit having a power control coupled to the dimming controller output to receive the dimming controller signal. The full power circuit also has a full power output that can couple to the lamp. When the full power circuit receives the dimming controller signal, via the power control, and the dimming controller signal is not in the dimming request range (i.e. the full illumination mode has been selected), the full power circuit generates a full power signal capable of driving/operating the lamp(s) in the full illumination mode. A filament heating circuit has a heating input coupled to the reduced power circuit, to receive the reduced power signal, and a heating output that can couple to the filaments of one or more lamps. When the reduced power signal is present, the filament heating circuit generates and provides a filament heating signal to the filaments, via the heating output. The filament heating signal maintains the temperature of the filaments when the lamp(s) are operated in the dimmed illumination mode. Further, the filament heating signal is responsive to the reduced power signal.