A unity power factor electronic ballast for fluorescent lamp having improved valley fill and valley boost converter

A new PF correction topology, improved valley fill (IVF) with valley boost converter (VBC) used in the electronic ballast for a fluorescent lamp is presented. Different from the conventional valley fill, the IVF has different charging operation to the electrolytic capacitors and can adjust the valley voltage higher than half the peak line voltage. Hence, there is no pulsating line current around the line voltage peak, PF and THD are significantly improved. The IVF also improves lamp current crest factor (CF) by the energy transfer action. The VBC is added to the IVF to achieve unity PF and to increase the valley voltage. The VBC operates only during valley region to decrease the loss of switching devices and the voltage stress of the resonant inverter. The VBC can be constructed with small size and low cost having very simple controller. The measured PF and THD for a prototype electronic ballast are 0.997 and 5%, respectively, and the lamp current CF is as low as 1.5