An apparatus and method for powering a lamp connected to a ballast
circuit. The ballast circuit is connected to a first alternating current
(AC) source having a first phase and to a second AC source having a
second phase. A first rectifier circuit is connected between the first AC
source and a first switching circuit. A second rectifier circuit is
connected between the second AC source and a first switching circuit. A
control circuit selectively energizes the first and second switching
circuits to provide power from the first and second AC sources to the
lamp load via an inverter circuit. A detection circuit generates a
detection signal indicating whether power is being supplied by each the
first and second AC sources. The detection signal is provided to a
dimming regulation circuit to generate a dim level command signal for
dimming the lamp.