Three-switch LLC resonant converter for high efficiency adapter with universal input voltage

Abstract

In this paper, an LLC resonant converter using three metal-oxide-silicon field-effect transistor (MOSFET) switches is proposed for high efficiency with universal input voltage. At high line input, the proposed converter operates same as the conventional half-bridge (HB) LLC converter. At low line input, by changing the operation of three switches, the resonant tank of the proposed converter is divided into two resonant tanks and turns-ratio of the proposed converter is changed to half. As a result, the DC voltage gain is doubled for the low line input, which enables the proposed converter to be designed with large magnetizing inductance (Lm). Therefore, the proposed converter has low conduction loss and low turn-off switching loss over the entire input voltage range. The proposed converter is verified by experimental results with 90Vac~264Vac input and 45W/19V output prototype.