A ballast control circuit for multiple lamps comprising a ballast 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 an output
circuit comprising a plurality of parallel connected lamps; the control
circuit comprising an oscillator, the 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; a lamp output voltage being
developed across the output circuit; further comprising a feedback
circuit for controlling the oscillator whereby the oscillator sweeps from
a first frequency above resonance to a lower frequency closer to
resonance 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.