A circuit for dimmably driving fluorescent lamps (102, 104, 106) from a DC supply voltage includes: input nodes (174, 176) having input capacitors (184, 186) connected therebetween; a half-bridge transistor inverter (178, 180) connected between the input terminals; a series-resonant LC oscillator (196, 198) coupled in series between the half-bridge transistors and the input capacitors; an output transformer (212) having a primary winding (214) connected in series with the LC inductor (196) and in parallel with the LC capacitor (198) and a secondary winding (216) for connection to the lamp load; and first and second voltage clamp diodes (215A, 215B) connected between an intermediate point on the primary winding and the input nodes respectively. The voltage clamp diodes, in conjunction with the input capacitors, provide significant enhancement in reduction of power transferred to the lamps when the DC supply voltage is reduced, allowing lamp dimming to be simply and efficiently effected by reduction of the DC supply voltage.