Control of a Merged-Energy-Buffer based Two-Stage Electrolytic-Free Offline LED Driver

This paper presents the control techniques used in a high-power-density electrolytic-free offline LED driver that utilizes a merged energy buffer for twice-line-frequency energy buffering. This LED driver comprises two stages: a four-switch buck-boost PFC stage and an LLC resonant dc-dc stage. The proposed control technique for the PFC stage utilizes a novel mode splitter to ensure a smooth buck-to-boost and vice versa mode transition. A feedforward control strategy is proposed for the dc-dc stage, which in conjunction with feedback control, ensures a well-regulated output voltage by mitigating undesirable spikes in it. A 150-W prototype LED driver utilizing a merged energy buffer is tested with the proposed control techniques. This GaN-based prototype achieves a high power density of 50 W/inch3 while replacing electrolytic capacitors with low-energy-density ceramic capacitors.