An Improved Modified Sepic Converter for High-Luminance Lighting LED Lamps

The efficiency and lifetime of light-emitting-diode (LED) lamps are approaching and exceeding that of fluorescent lamps. LED light sources are finding more applications than conventional light bulbs due to their compactness, lower heat dissipation, real-time color changing capability and most importantly, long life which is much longer life than that of conventional offline power converters. In these offline applications, high power factor, and low harmonics are of primary importance. The modified SEPIC-type PFC not only can achieve unity power factor but reduce dc-link voltage to release component stresses. Therefore, it is suitable for high line-voltage applications. It is also important to step up/down voltage with simple single-stage conversion for low cost and high efficiency. A SEPIC converter is particularly suitable for non-isolated application since it is single stage, and can step up/down, and of high power factor as it is run in discontinue conduction mode. The harmonics of the input line current is reduced and power factor is high because the input inductor current follows the input voltage. A current feedback loop is proposed to control the LED brightness. This circuit has the advantages of one stage of power conversion, no need to sense the input voltage, simple feedback control, voltage step-up and down, high power factor and dimmable LED current. Keywords— SEPIC Converter, LED, MATLAB, Constant Current Control, Stability