Single-Stage LED Driver Achieves Electrolytic Capacitor-Less and Flicker-Free Operation With Unidirectional Current Compensator

AC-connected light emitting diode (LED) drivers experience imbalanced energy between input and output in a half-line cycle. To achieve the flicker-free operation, the imbalanced energy needs to he buffered, often by energy-dense electrolytic capacitors. However, electrolytic capacitors are also well-known for their short lifespan. These capacitors are the limiting factor of an LED drivers' lifespan. High voltage film capacitors and a buck converter have been used in the proposed LED driver to buffer the imbalanced energy. When P-in > P-LED, the extra energy is transferred from the ac input directly to the high voltage film capacitors. When P-in < P-LED, the energy is transferred from the high voltage film capacitors to the output by the buck converter. The imbalanced energy goes through two power conversion steps in the proposed LED driver, which is one time less than other comparable electrolytic capacitor-less designs, enabling a higher efficiency to be achieved. A 28 W flyback topology based experimental prototype had been built and tested to verify the proposed design.