A Single-Stage Electrolytic-Capacitor-Free AC-DC LED Driver With High Power Factor and Soft Switching Characteristics

This article proposes a single-stage ac/dc converter for driving high-power light-emitting diodes. The circuit topology mainly includes two modified Cuk converters that are interleaved operated. The front semi-stage of Cuk converter operates like a boost converter while the second semi-stage operates like a buck converter. The boost converters are operated in discontinuous-conduction mode to play the role of power factor corrector. In the buck converters, the two energy-storage inductors are replaced by a coupled inductor. The mutual inductance current of the coupled inductor is almost constant and continuously flows to the output terminal. Therefore, the output voltage ripple can be effectively reduced without using large electrolytic capacitors. In addition, the proposed circuit does not require the use of any snubber circuit or active clamping circuit. All active switches operate at zero-voltage switching ON, and all diodes operate at zero-current switching OFF. This article analyzes the operation modes of the circuit; derives mathematical equations; and designs component parameters. Finally, 180-W prototype circuit was built and tested. The experimental results show that the conversion efficiency at rated power operation is 96.6%; the power factor is as high as 0.996; and the total harmonic distortion of current is 7.18%. The performance is satisfactory and verifies the feasibility of the proposed circuit.