A compact electrolytic-free two-stage universal input offline LED driver

This paper presents a single phase, two-stage electrolytic-free offline LED driver that utilizes a hybrid film-ceramic stacked switched capacitor (SSC) energy buffer (EB) in place of limited-life electrolytic capacitors for twice-line-frequency energy buffering. The proposed LED driver comprises a front-end power factor correction (PFC) stage, followed by an isolated dc-dc conversion stage, with an SSC energy buffer connected across the intermediate dc bus. Compared to a single capacitor, the use of SSC energy buffer reduces the passive volume of the energy buffer by a factor of two. A simple and robust control scheme is proposed to interface the SCC energy buffer with the PFC converter. A prototype 300 W LED driver for universal input voltage range (90-265 Vrms) and 12 V output voltage is designed, built and tested based on the proposed architecture. The SSC energy buffer achieves a peak efficiency of 98.5% and maintains an efficiency of above 96% across a wide output power range, thus minimally impacting the overall system efficiency. In addition, the impact of the intermediate dc bus voltage ripple on overall system efficiency is investigated. It is found that there is negligible change in overall system efficiency when the intermediate bus voltage ripple ratio is varied between 3% and 7.5%.