Miniaturized Bridgeless High-Frequency Resonant AC–DC Step-Up/Step-Down Converters

This paper introduces two bridgeless resonant ac-to-dc converters to efficiently convert arbitrary input voltages into a regulated dc output voltage. The proposed topologies provide direct ac–dc power conversion with less number of components, in comparison to other resonant topologies. The converters utilize soft-switched LC networks and diodes to convert low-frequency and low-amplitude alternating input voltage into a dc output voltage. Zero-voltage switching (ZVS) and zero-current switching (ZCS) are achieved in switching both power transistors and diodes. High-frequency soft-switching operation due to LC resonance allows smaller footprint for passive components, thereby increasing the circuit power density without suffering from switching losses. A resonant gate drive circuit is designed and utilized to further reduce gating losses under high-frequency switching and light-load condition. The converters operate at a fixed switching frequency, while they regulate the output voltage by using module pulsewidth-modulated (PWM) on-off control with fast transient response. A 5-mm × 6-mm, 100-mg prototype is fabricated, which is operating at 2-MHz switching frequency. The maximum output power of the prototype reaches 650 mW, with a 3-
$V_{\rm rms}$
ac input voltage and a 7.6-V dc output voltage. The converter achieves higher than 70% closed-loop efficiency across wide range of input voltages and output powers.