review of various proposed schemes to increase the reliability and life span of solid-state lighting (SSL) systems is presented in this article. Since the mainstream devices employed for such lighting systems are inorganic, high-power light-emitting diodes (LEDs), which are devices characterized by their very long life, most of the questions in reliability and endurability arise from the electronic offline circuit driving the LEDs. Issues regarding the limited reliability of specific components, such as electrolytic capacitors, are introduced. Several power-conversion configurations aimed to capacitance reduction and capacitor technology exchange are put forward as alternative solutions for implementing long-life drivers, with remarks on both their benefits and drawbacks. An extensive literature review on the topic
This paper presents a new control method and a detailed project methodology for the optimized connection method of two converters, aiming to reduce the redundant power processing, in order to supply high power LEDs with reduced capacitance and high efficiency, directly from the AC line. This connection method allows dealing with two major issues related to the LED driver: capacitance reduction and efficiency increasing. The first converter provides Power Factor Correction (PFC), while the second converter controls the current through the LED. The basic idea consists in making the second converter to process only the low frequency ripple of the first converter, thus smoothing the LED current. In this way, the low frequency ripple is managed by the second stage so that the capacitance of the first stage can be significantly reduced. The proposed control method can achieve better results for the low frequency compensation. Besides that, a high power factor and a low harmonic content are obtained, fulfilling the IEC 61000-3-2 class C requirements. A laboratory prototype with a rated power of 75 W and an input voltage of 220 Vrms/60 Hz was built in order to show the feasibility of the idea. The measured overall efficiency of the converter was 91% and electrolytic capacitors were avoided.
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