Ceramic capacitor controlled resonant LLC converters

The possibility of applying standard commercial ceramic capacitors for controlling a resonant LLC converter was studied analytically and experimentally. Using a two serially connected ferroelectric capacitors assembly, experiments were run on a mockup of an LLC converter that was switched at 90kHz to a power level of 5W. The voltage dependent capacitors had a range of 95nF-320nF for a bias span of 0–100V. A DC bias driver with a high output impedance that is suitable for controlling the voltage dependent capacitors is proposed and discussed. The theoretical considerations and experimental results of this study suggest that ferroelectric ceramic capacitors could be a viable control element of resonant LLC converters running at a fixed switching frequency.