Optimization of a Front-End DCM Buck PFP for an HPF Integrated Single-Stage LED Driver

There is currently a trend in power electronics to avoiding the use of electrolytic capacitors in LED drivers, provided that their expected life span is much lower than that of the LEDs, thus reducing the reliability of the entire LED fixture. This paper presents an optimization study about the determination of the minimal bus capacitance needed for reducing the power factor preregulator (PFP) stage dc-link capacitor down to values that are available in metalized-film technology. This optimization study will be applied to the buck converter, which is an interesting topology for high power factor (HPF) LED drivers due to its low component count, HPF, low output voltage, and lower voltage stress on semiconductors than the boost or buck-boost PFPs, which yields to lower efficiency decline under dimming operation. This way, a 70-W integrated buck-flyback converter is developed and proposed with an metalized-film polypropylene (MKP) dc-link capacitor, intended for outdoor applications where a high reliability is pursued, and capable of driving several LED lamps in different configurations. The experimental results show the accuracy of the theoretical predictions, confirming the feasibility of the buck converter as a high-performance PFP.