An AC-DC LED Driver With High-efficiency Active Power Decoupling Circuit

Light-emitting diode(LED)lamps are expected to dominate the lighting market due to their advantages of high efficiency and long lifespan.Since most LED lamps are powered by the single-phase utility grid and LEDs should be driven by constant current,a dedicated LED driver is required to achieve power foctor correction and current regulation,which is generally realized by an AC-DC converter.In traditional AC-DC LED drivers,the inherent double-line-frequency ripple power from the ac source is isolated from the load by large electrolytic capacitors which make the lifespan and reliability of LED lighting systems suffer.Therefore,the research on electrolytic capacitor-less LED drivers has attracted a lot of attention.This thesis presents an electrolytic capacitor-less AC-DC LED driver with a unidirectional active power decoupling circuit for ripple power isolation.The active power decoupling circuit processes a much lower power in the proposed LED driver than other similar designs,which enables power loss reduction.The topology and the operating principle of the proposed AC-DC LED driver are introduced in detail.The circuit analysis and the parameter determination is also presented,considering the characteristics of the ceramic capacitors.In addition,two high-efficiency active power decoupling circuits are proposed for the AC-DC LED driver.The Buck-Boost active power decoupling circuit includes fewer components and has a simple structure.The resonant switched-capacitor active power decoupling circuit can achieve higher efficiency due to the zero current switching(ZCS)operation.Furthermore,due to the high switching frequency(about 5 MHz),the size of passive components in this circuit is small.Therefore,the circuitry can be built on a wafer.In this thesis,the operating principle,parameter design and control design of the proposed active power decoupling circuits are introduced in detail.The simulation is performed to verify the theoretical analysis.The prototype is built,and experimental waveforms and measurement results are given to verify the proposed AC-DC LED driver with active power decoupling circuits.