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 DC-link voltage. The switching frequency is controlled to maintain the DC-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 power converter operating in the discontinuous conduction mode, which naturally provides HPF to the utility line. The fluorescent lamps are driven by an unmodulated sine-wave current generated from an LC parallel resonant power 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 DC-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.