Filter Capacitor Minimization in a Flyback LED Driver Considering Input Current Harmonics and Light Flicker Characteristics

In this paper, a comprehensive study is conducted on reducing the size of output filter capacitor in an ac-dc flyback converter for driving high-brightness LED strings. To this end, a relationship between the input current harmonics, LED light flicker, and the magnitude of filter capacitor is obtained. It is shown that the size of the filter capacitor is mostly affected by the amplitude of the third and fifth harmonics of input current and the output light flicker. Considering the EN61000-3-2 standard for input current harmonics content and ENERGY STAR standard for flicker requirement, a procedure for obtaining the minimum value of filter capacitance is presented. Experimental studies are performed on an ac-dc flyback LED driver using the proposed method and tested on Cree XLamp XP-G and CR22-32L LED strings.