Resonant assisted buck converter for offline driving of high brightness LED replacement lamps

LEDs are prospective successors of incandescent lamps with high efficacy and long lifetime. To improve the overall luminair efficacy and lifetime, the power efficiency and lifetime of LED ballast become important factors. Efficiency gain in transformerless power converter appears attractive for applications without isolation. Driving solid-state LED bulbs such as in PAR30 style from universal mains necessitates a high voltage step-down ratio to an output voltage of about 10-20 V, which is very common in industrial applications. Traditional step-down PWM buck power converter may suffer from a poor efficiency due to long diode freewheeling at a small duty cycle. In this paper, we propose a resonant assisted buck converter to achieve high voltage step-down ratio and high converter efficiency, whilst it can work with existing dimming drivers. The performance of the proposed LED driver is verified by a prototype ballast.