High power factor electronic ballast with constant DC link voltage

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