Wide Voltage-Regulation Range Synchronous-Rectifier <i>LLC</i> Converter With Novel Operation Modes

Traditionally, the energy feedback in synchronous rectifier (SR) LLC converter was once considered to only have the ability to reduce the voltage gain. In this article, a kind of special energy feedback caused by the novel operation modes of LLC resonant converter is proposed for improving voltage gain. Compared to the P, O, and N stages in conventional LLC converter, stage F is built by controlling the turn-on early time of the SR. By using the proposed operation modes, not only zero-voltage switching (ZVS) of both the primary-side and secondary-side switches is achieved, but the voltage gain of the LLC converter can be increased significantly with a narrow switching frequency range and a smaller magnetizing inductance circulating current. In addition, the proposed operation modes are simple and easy to be utilized in full bridge, half bridge, and so on; all kinds of LLC converters thus can form a new general control strategy of the SR LLC. Finally, a 100-W half-bridge SR LLC dc-dc converter prototype with a wide voltage-regulation range is implemented to validate the proposed operation modes and the theoretical analysis.