Abstract: A dimmable fluorescent lamp system comprises a fluorescent lamp with filaments at each end that are continuously heated by a transformer. A resonating capacitor is connected in series with a resonating inductor and a pair of DC blocking capacitors are connected from each end of the fluorescent lamp to put it in parallel with the resonating capacitor. A control logic drives the resonating inductor with a pulse-width modulated square wave that is controlled by a feedback voltage derived from a pair of rectifiers and a dropping resistor in series with one of the DC blocking capacitors. An error amplifier with two gain settings, e.g., one for a range of 0-20% of maximum light dimming and the other for 20%-100% dimming, compares the feedback voltage to a setpoint. A threshold comparator establishes the switchover point between the two error gain ranges.

Abstract: A dimmable fluorescent lamp system embodiment of the present invention comprises a fluorescent lamp with filaments at each end that are continuously heated by independent secondary windings of a transformer. A resonating capacitor is connected in series with a resonating inductor and a pair of DC blocking capacitors are connected from each end of the fluorescent lamp to put it in parallel with the resonating capacitor. A control logic drives the primary winding with a pulse-width or frequency modulated square wave that is controlled by a feedback voltage derived from a pair of rectifiers and a dropping resistor in series with one of the DC blocking capacitors.