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While LEDs enjoy relatively long lifetime up to 10 years, the lifetime of traditional LED drivers using electrolytic capacitor as storage element is limited to typically less than 5 years. In this paper, an ac/dc LED driver without electrolytic capacitor is studied. Compared with other methods to eliminate electrolytic capacitor, the proposed driver has the advantages of almost unity input power factor and constant output current for LEDs. The operation principle, detailed design procedure of the main circuit, and control strategy are presented. The feasibility of the proposed converter has been successfully verified by experiments.