An electrolytic-free offline LED driver with a ceramic-capacitor-based compact SSC energy buffer

This paper presents the design and implementation of a compact ceramic-capacitor-based stacked switched capacitor (SSC) energy buffer for a single-stage offline 8-W 21-V output electrolytic-free LED driver. The elimination of the electrolytic capacitors can lead to a longer lifetime for the LED driver. Compared to earlier works, this design of the SSC energy buffer has a simpler ground-referenced gate drive circuit and eliminates the need for a separate precharge circuit. The prototype LED driver presented here uses a ceramic-capacitor-based SSC energy buffer with optimized capacitor sizing that provides substantially higher effective energy density than electrolytic capacitors. The improvement in energy density is achieved in part by a design approach which optimizes the ratio of the capacitance values of the capacitors in the SSC energy buffer. The prototyped SSC energy buffer achieves a round-trip efficiency of above 98%. The total passive volume of the ceramic capacitors in the prototype is less than half the volume of the electrolytic capacitors it replaces.