Power supply for supplying AC output power

High voltage stress on the semiconductor devices at light load conditions, high total harmonic distortion (THD) of the line current, and poor crest factor (CF) of lamp current of ''charge pump'' electronic ballast circuits make them difficult to manufacture cost-effectively. To overcome these deficiencies, the DC bus voltage is reduced at light loads by providing a second resonance. One technique, high-frequency second-stage resonance, provides sufficient preheating at low V.sub.dc. Combined with the instant startup and the proper restart scheme, this technique can greatly reduce the maximum V.sub.dc at ignition. Another technique, low-frequency second-stage resonance, can reduce the steady state V.sub.dc at light loads, including during start-up. Consequently, high ignition voltage can be continuously impressed on the lamp without increasing V.sub.dc. Further, a diode clamping technique smooths the envelope of V.sub.a, thereby achieving near unity power factor, low THD and low CF without close-loop control.