An Input-Coupling LLC Converter With Wide Input Voltage Range and High Efficiency

The LLC full-bridge converter is a highly efficient solution for high-power secondary power supply applications. It is known for its low stress operation and reduced electromagnetic radiation. However, it has a relatively narrow optimized switching frequency and is very sensitive to input voltage variations, particularly at low input voltage conditions. Achieving a balance between a wide input voltage range and high efficiency is challenging. This article proposes an input-coupling type LLC converter (IC-LLC) as a solution. The resonant converter shares the input voltage with a pre-stage. Power is transferred through the prestage during half of the switching cycle, while the resonant stage takes charge during the other half cycle. This results in an improvement in the efficiency of the converter. A 1.5-kW IC-LLC converter system was built and tested. Experimental results show that the input coupling mechanism significantly enhances the efficiency of the dual-stage conversion setup, overcoming the operational challenges associated with LLC converters.