High-Efficiency LLC Resonant Converter With High Voltage Gain Using an Auxiliary LC Resonant Circuit

To design an LLC resonant converter optimally in the wide input voltage range, the LLC resonant converter with high efficiency and high voltage gain using an auxiliary LC resonant circuit is proposed. In this paper, the auxiliary LC resonant circuit operates as a variable inductor according to the change of the switching frequency, and it is presented as an effective magnetizing inductance. In the nominal state, since the effective magnetizing inductance increases, the primary circulating current is decreased. Thus, the turn-off switching loss of the primary switches and the primary conduction loss are minimized. During the hold-up time, the effective magnetizing inductance decreases so that the proposed converter has a high voltage gain. As a result, an optimal design of the LLC resonant converter over the wide input voltage range is possible. The proposed converter is verified by experimental results with a 330-390 V input and 350 W(56 V/6.25 A) output prototype.