Patent ID: 7352139
Filing Date: 2008-04-01
Classification: H05B

Abstract:
1. A ballast control circuit for a plurality of parallel connected lamps, the circuit comprising: a control circuit for driving two series connected switches of a lamp ballast connected across a supply potential and having a switched node between the switches, the switched node adapted to be connected to each of the plurality of parallel connected lamps, the control circuit comprising an oscillator; an output circuit comprising the plurality of parallel connected lamps including inductive and capacitive components and having a resonance frequency that is dependent on the number of lamps in the output circuit, an output voltage being developed across the output circuit; and a feedback circuit for controlling the oscillator whereby the oscillator sweeps from a first frequency above the resonance frequency to a lower frequency closer to the resonance frequency such that the output voltage increases to a potential above a lamp ignition threshold, thereby igniting at least one lamp, the feedback circuit controlling the oscillator whereby the oscillator frequency reduces each time a lamp ignites, causing the output voltage across the output voltage circuit to increase above the threshold, thereby igniting another of the lamps.