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

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 (L
_m
). 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 90V
_ac
~264V
_ac
input and 45W/19V output prototype.