Feedforward compensation of resonant converters with heavy ripple in the DC bus for LED lamp driver applications

For reliability reasons, electrolytic capacitors are not recommended in electronic drivers for light emitting diodes (LEDs). This design constraint is difficult to fulfill, especially at medium to high-power levels. In this paper, the proposed driver is composed of two stages. The input stage is a low-cost valley-fill power factor corrector stage, which produces a DC-link voltage with a heavy ripple. The output stage is a phase-controlled LC
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C
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resonant converter. The effect of the voltage ripple on the output current is cancelled out by a feedforward action. The DC-link input voltage is sensed in order to shift the phase, Ψ, of the transistor drive signals of the converter. The fast dynamics of the resonant stage ensures an operation free of instabilities and flicker effects. A 120W prototype has been built to validate the design proposal.