Preheating circuit for detecting the filament temperature of fluorescent lamps

摘要

A preheating circuit for a fluorescent lamp is provided. The preheating circuit includes a filament detecting circuit indirectly detecting a filament resistance in a fluorescent lamp by measuring a filament voltage and a filament current, a pulse generation circuit providing pulses of one of a first frequency and a second frequency determined by the detected filament resistance and a specific filament resistance, and a filament resonance circuit operating the fluorescent lamp at an operating frequency determined by the pulse generation circuit. Therefore, the filament resonance circuit operates at the first frequency to preheat the fluorescent lamp when the detected filament resistance is smaller than the specific resistance. The filament resonance circuit operates at the second frequency to operate the fluorescent lamp when the detected filament resistance is one of a first value being larger than and a second value being equal to that of the specific resistance.