| 摘要 |
<p>A ballast system for at least one dimmable lamp (10,12) has a filament-heater power supply including a combination forward and flyback power converter for supplying electronically variable, isolated voltages to dimmable discharge lamp filaments (10a,10b,12a,12b) while supplying a fixed dc output voltage to a ballast control circuit (22). Hence, only a single ballast power supply is needed. The control circuit (22) controls the level of filament voltage to operate the lamp filaments (10a,10b,12a,12b) at an optimum temperature, even during dimming operation, thereby substantially extending lamp life. The filament-heater power supply (18) provides a high degree of isolation among filament voltages while regulating and tracking the voltage across each filament (10a,10b,12a,12b). The filament-heater power supply (18) can preheat the filaments (10a,10b,12a,12b) to aid lamp starting, thereby extending the useful life of the lamp, and is also structured to sense when a lamp (10,12) is not present in a fixture so that high voltage starting pulses are not applied to the terminals of an empty fixture. <IMAGE></p> |
