High-Efficiency LLC Resonant Converter With Reconfigurable Voltage Multiplying Rectifier for Wide Output Voltage Applications

This article presents a reconfigurable voltage multiplying rectifier (RVMR) to improve the performance of an LLC resonant converter for wide output voltage applications. The RVMR can operate as voltage-doubler mode or voltage-quadrupler mode according to the primary switching strategy. Two operation modes split a wide output voltage range into two narrow ranges. Therefore, the RVMR enables the LLC resonant tank to be designed in a narrow output voltage range, which results in a narrow switching frequency range, high efficiency, and high power density. A smooth mode transition can be achieved by adopting a phase-shift control to general pulse frequency modulation control without any additional switch. The proposed RVMR LLC converter can improve its efficiency by 2.9% and reduce component volume by 26% compared to the conventional full-bridge LLC resonant converter. A 750-W prototype with 400 V input, 100-300 V output voltage, and 2.5 A max output current has been built and tested to verify the effectiveness of the proposed converter.