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A Dimmable Electronic Ballast With Unity Power Factor Based on a Single-Stage Current-Fed Resonant Inverter

A single-stage dimmable electronic ballast with very high power factor and high efficiency is presented in this paper. A compact lamp power circuit is designed by integrating a buck-boost power factor corrector with a current-fed resonant inverter. This integration produces a single power-processing unit that minimizes the number of circuit components. The proposed resonant inverter reduces the circulating current in the resonant tank and allows simple gate drivers to be used so that isolation devices can be eliminated. With the buck-boost stage operating in the discontinuous conduction mode (DCM), a close-to-unity power factor is achieved for different lamp-power conditions. A small-signal analysis is presented, and a simple variable frequency controller is developed using the modified 555 timer to provide dimming operations. Simulation and experimental waveforms are provided to highlight the merits of the proposed circuit for a 40-W compact fluorescent lamp.