High-power-factor electronic ballast with constant DC-link voltage

This paper presents a high-power-factor (HPF) electronic ballast based on a single power processing stage with constant de-link voltage. The switching frequency is controlled to maintain the de-link voltage and the voltage across the switches constant, independently of changes in the ac-input voltage. This control method assures zero-voltage switching (ZVS) for the specified ac-input-voltage range. Besides, with an appropriate design of the fluorescent lamps' drive circuit, the lamps' power can be kept close to the rated value. The power-factor-correction (PFC) stage is formed by a boost converter operating in discontinuous conduction mode, which naturally provides;HPF to the utility line. The fluorescent lamps are driven by an unmodulated sinewave current generated from an LC parallel resonant converter, which operates above the resonant frequency to perform ZVS, Theoretical analysis and experimental results are presented for two series-connected 40-W fluorescent lamps operating from 127 V -15% to +10% 60-Hz utility line. The switching frequency is changed from 25 to 45 kHz to maintain the de-link voltage regulated at 410 V, which leads to a constant output power. The experimental results confirm the high efficiency and HPF of this electronic ballast.