Three-Switch LLC Resonant Converter for High-Efficiency Adapter With Universal Input Voltage

The LLC resonant converter is one of the most attractive topologies in many applications, due to its simple structure and zero-voltage-switching capability. However, under wide-input-voltage condition, it has large primary conduction and turn-off switching losses because of small magnetizing inductance. Thus, in this article, the LLC resonant converter using three switches is proposed for high-efficiency under wide universal ac input voltage. These three switches can make two operating modes of LLC resonant converter according to low/high line input conditions. As a result, the proposed converter can be designed with larger magnetizing inductance, resulting in high efficiency. The validity of the proposed converter is verified with a 60-W prototype for high efficiency, almost maintaining the system size, compared with the conventional LLC converter.