A merged-stage high efficiency high power factor HB-LED converter without electrolytic capacitor

This paper introduces a merged converter topology for supplying high-brightness light-emitting diodes for lighting applications. The converter combines a boost-based power factor correction rectifier (PFC) and a resonant converter in a single-stage. In this topology both converters share the same switching components and a bulky electrolytic capacitor, existing in conventional systems, is replaced with a small film capacitor. These modifications result in a smaller volume and number of components, compared to other 2-stage topologies. The intermediate energy storage capacitor is reduced by allowing a large voltage ripple across it and storing a portion of energy in the resonant part of the converter. The converter is regulated by a digital controller implementing a variable frequency variable-duty-ratio control algorithm. Constant light output and dimming capability are obtained by varying the frequency of the resonant part. The duty ratio control is used at the front end of the converter, to obtain power factor correction. Experimental results with a 15 W prototype verify reliable operation with a small film capacitor, near unity power factor, and high efficiency, varying between 88% and 90% over the entire operating range.