High-power-factor LED driver based on input current shaper using a flyback converter

This paper presents a high-power-factor LED driver implemented by using an input current shaper. A DCM-operated flyback converter is placed between the main rectifier and DC bus, in order to increase the conduction angle of the rectifier diodes and to obtain low current harmonics injected to the mains. Power control stage is performed by a buck converter, which is integrated with the flyback, thus presenting reduced component count. The use of a flyback converter operating as a loss free resistor provides reduced power processing, which increases overall efficiency of the converter. In addition, two-stage configuration allows for bus capacitor reduction, owing to the effect of low frequency filtering provided by the second stage. In this way, electrolytic capacitors can be avoided, thus increasing reliability of the LED driver, which is an essential feature pursued in this type of converters. Analysis and design example of the proposed converter are presented. Experimental results of the proposed converter supplying two 25 V / 2.1 A LEDs are shown. The prototype presented high power factor, PF=0.97, total harmonic distortion of input current satisfying the IEC 61000-3-2 requirements, THD=21.1%, and high efficiency, η=91,2%.