Offline SEPIC converter to drive the high brightness white LED for lighting applications

Abstract

High brightness white LED has attracted a lot of attention from both industry and academia for its high efficacy, simple to drive, environmentally friendly, and long lifespan. It becomes possible applications to replace the incandescent bulbs, halogen bulbs, and even compact fluorescent light bulbs in residential, industry and commercial lighting. Offline application of this new lighting source requires both tight LED current regulation and high power factor as well. We proposed an interleaved SEPIC converter with integrated magnetics for the offline LED lighting applications with LED current dimmable and input power factor correction. The converter is controlled with voltage mode PWM and run in discontinuous conduction mode. The inductor current follows the input voltage, therefore, the converter has high power factor, and can handle high power with reduced number of component count. This circuit has the advantages of (1) one stage of power conversion, (2) high power factor, (3) reduced size of the input filter, (4) reduced size of output filter, (5) integrated magnetic components, and reduced component count, (6) simple feedback control and no need to sense the input voltage, (7) voltage step-up and down, and (8) dimmable load current. It is particular suitable for the non-isolated offline applications, such as high brightness LED lighting applications. The critical design constraints and equations for both the power stage and control loop are highlighted and detailed. A practical evaluation board with 110 V input and 60 V 700 mA output is developed to verify the proposed design.