Power supply for supplying AC output power

摘要

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 Vdc. Combined with the instant startup and the proper restart scheme, this technique can greatly reduce the maximum Vdc at ignition. Another technique, low-frequency second-stage resonance, can reduce the steady state Vdc at light loads, including during start-up. Consequently, high ignition voltage can be continuously impressed on the lamp without increasing Vdc. Further, a diode clamping technique smooths the envelope of Va, thereby achieving near unity power factor, low THD and low CF without close-loop control.