A Magnetically Controlled Single-Stage AC-DC Converter

In this letter, a magnetically controlled single-stage ac-dc converter is proposed for low-power application which has the following features. First, single-stage operation is achieved by sharing switches between LLC resonant converter and totem-pole bridgeless power factor corrector (PFC) converter. Second, the power factor correction function is inherently achieved by designing the PFC converter to operate in discontinuous conduction mode. Third, the dc-link voltage is almost constant. Fourth, fixed switching frequency and duty cycle can be implemented for the switches, which simplifies the magnetic component and driver circuit design. Fifth, the LLC resonant converter is designed to operate at series resonant frequency, the highest efficiency operating point, so the converter can always achieve the maximum efficiency operation. Meanwhile, at this operating point, the converter output voltage is independent of the load so that it is functioning as a dc transformer; and finally, soft switching for all semiconductors is achieved. A 75-W experimental prototype is built to validate the proposed magnetically controlled single-stage ac-dc converter.