Abstract: A driving circuit system for a gas discharge lamp includes a power circuit having a switch for converting an input voltage into a lamp voltage for driving the gas discharge lamp, a lamp current detecting circuit connected to the power circuit or the gas discharge lamp for detecting a lamp current, a feedback circuit connected to the lamp current detecting circuit for generating a lamp current feedback signal, a constant power control circuit for generating a corrected current reference signal, and a power control circuit connected to the feedback circuit, the constant power control circuit, and the switch of the power circuit for generating a first modulating signal in accordance with the lamp current feedback signal and the corrected current reference signal for driving the switch to turn on or off, thereby substantially maintaining a lamp power of the gas discharge lamp at a constant value.