Abstract: A circuit (100) for driving an instant-start fluorescent lamp (102) has an inverter (103, 132) and a series-resonant LC oscillator (146, 152). A capacitor (190) begins charging after power-up of the circuit and when its voltage reaches a certain level causes breakdown of a diac (192), which discharges the capacitor into an inverter transistor (132) to trigger operation of the inverter. Re-triggerring of the inverter is prevented by a diode (194) which subsequently discharges the capacitor cyclically, and by a capacitor (186) which enables a transistor (180) at a predetermined time following power-up. The occurrence of a subsequent fault condition causes a capacitor (210) to charge and to enable a transistor (196) which disables the inverter. Charging of the initiating capacitor (190) is prevented by an open circuit between terminal connectors (160, 162) if the lamp is not present.

Abstract: A circuit (100) for driving fluorescent lamps (102, 104, 106) and including: a half-bridge inverter (112) receiving a unidirectional voltage and producing an alternating voltage, and having control inputs (156, 166); a series-resonant oscillator (126) coupled to the inverter output (116) for producing an alternating signal; and a non-saturating feedback transformer (146) having a primary winding (148) coupled in series between the inverter and the oscillator and secondary winding (150, 152) coupled respectively to the control inputs of the inverter. Since the feedback transformer is non-saturating it provides to the inverter control inputs a linear feedback signal from the inverter. This results in safe, stable, predictable and well-defined circuit operation, in which the possibility of the inverter transistors being destroyed by cross-conduction is substantially removed, and the amount of input voltage "ripple" present in the signal applied to the lamps is reduced.

Abstract: A circuit (500) for driving two or more series-connected gas discharge lamps, having: an oscillator (518, 520, 522); and a transformer (524) with a primary winding (526) and a secondary winding (528). The transformer secondary winding has first (129A) and second (129B) points connected respectively to first (508) and second (514) output terminals across the series-connected lamps. A capacitor (532) couples the first point of the transformer secondary winding to an intermediate output terminal (112). The voltage produced by the secondary winding thus drives the lamps in series, while the pre-strike voltage produced across the secondary winding is applied across a single lamp (106) to cause it to strike. After striking, current to the intermediate output terminal (512) is limited by the capacitor (532). In this way, the voltage which needs to be produced across the secondary winding to ensure striking of all of the lamps is reduced.