In this work, an off-line flyback converter with PWM dimming function employing a single active power switch is proposed for LED lighting. The proposed converter is a slightly modified flyback topology which enables the main switch to be used both for power factor correction and PWM high-frequency dimming with a constant peak current on the LEDs, in order to conserve chromatic characteristics of the light emitted. The proposed control scheme uses duty-cycle to control the dimming level, while switching frequency is varied along to adjust the input power level and maintain a constant peak current on the LEDs. Mathematical description, simulation and experimental results of a prototype with 100 W of peak power fed from 127 V mains voltage are presented in this paper to show feasibility of the single-stage converter proposal.
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