A universal-input high-power-factor PFC pre-regulator without electrolytic capacitor for PWM dimming LED lighting application

High brightness white LED has attracted a lot of attention for its high efficacy, simple to drive, environmentally friendly, long lifespan and small size. The power supply for LED lighting also requires long life while maintaining high efficiency, high power factor and low cost. However, a typical design employs electrolytic capacitor as storage capacitor, which is not only bulky, but also with short lifespan, thus hampering the entire LED lighting system. To prolong the lifespan of power supply, it has to use film capacitor with small capacitance to replace electrolytic capacitor. In this paper, a universal input high efficiency, high power factor LED driver is proposed based on the modified SEPIC converter. Along with a relatively large voltage ripple allowable in a PFC design, the proposal of LED lamp driver is able to eliminate the electrolytic capacitor while maintaining high power factor. To increase the efficiency of LED driver, the presented SEPIC-derived converter is modified further as the twin-bus output stage for matching ultra-high efficiency twin-bus LED current regulator. The operation principle and related analysis is described in detail. A 50-W prototype has been built and tested to verify the proposed LED Driver.