Variable Frequency Multiplier Technique for High-Efficiency Conversion Over a Wide Operating Range

This paper presents a variable frequency multiplier (VFX) technique that enables the design of converters for wide input and/or output voltage ranges while preserving high efficiency. The technique is applied to an LLC converter to demonstrate its effectiveness for converters having a wide input voltage variation such as universal input power supplies. This technique compresses the effective operating range required of a resonant converter by switching the inverter and/or the rectifier operation between processing energy at a fundamental frequency and one or more harmonic frequencies. The implemented converter operates over an input voltage range of 85-340 V, but the resonant tank and conversion ratio have only been designed for half this range; a VFX mode of the inverter is used to enhance this to the full range. The experimental results from a 50-W converter show an efficiency of 94.9%-96.6% across the entire input voltage range, demonstrating the advantage of using this technique in such applications.