A Study of LLC Converter with Buck Converter for CC-CV Charging

For having switching frequency equal to resonant tank frequency in LLC converter, a unity voltage gain can be achieved over the entire loading conditions but it is not suitable for the Constant Current-Constant Voltage (CC-CV) battery application. Also, the voltage gain characteristic of LLC converter is frequency dependent. For battery charging application, a wide range of switching frequency is required for supplying constant current, charging the battery with its varying load characteristic. It causes above and below resonant frequency operation which causes losses and noise. As result, it is proposed to make use of a buck converter at the output of LLC converter for regulating the charging current and voltage for battery charging application.