A circuit (100) for driving a gas discharge lamp load (102, 104, 106) includes an inverter (112) receiving a unidirectional voltage and producing an alternating voltage, and having a control input (156, 166). A series-resonant oscillator (126) coupled to the inverter output (116) has an inductance (128) and a capacitance (130) in series for producing an alternating current. An output transformer (134) couples the lamp load to the oscillator in series with the inductance and in parallel with the capacitance. A feedback transformer (146) has a primary winding (148) coupled in parallel with the output transformer and in series with the capacitance, and has a secondary winding (150, 152) coupled to the control input of the inverter. Since the primary winding carries only capacitive current (IC), the frequency of the circuit is substantially independent of the load. This allows the feedback transformer to be of the non-saturating-core type while retaining control of the oscillator frequency. Also, the circuit automatically shuts down in the event of load short-circuit.