Multiple low-pressure discharge lamp operating circuit

Abstract

To operate at least one, and preferably a plurality of fluorescent lamps, a elf-oscillating transistor push-pull switching oscillator, using two similar transistors (T1, T2), is connected to respective lamps (3, 3', 3'), with an oscillatory circuit (4, 4', 4') to operate at audio, supersonic or low high frequency, for example in the 20 kHz range. Each lamp operating circuit has an individual series resonance circuit (4, 4', 4') which includes a ballast inductance (L1, L1', L1') and a capacitor (C1, C1', C1'). For multiple operation, the respective lamp operating circuits are connected in parallel. A special starting circuit (10) and a control circuit (9a, 9b; L2, L2', L2'; L3, L3', L3') for the switching transistors insures low-loss operation. The transistors (T1, T2) are the deenergized in case of malfunction by a monitoring circuit (11; L4, L 4', L4') which includes a thyristor (21) which fires to disable oscillatory operation of the oscillator circuit and thereby prevents over-voltage conditions upon electrical removal of a lamp load.