Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.

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Light-emitting diodes

A 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 is carried out, and some practical outcomes from recent research on offline LED driving are highlighted.

Matching LED and Driver Life Spans: A Review of Different Techniques

High-Brightness Light Emitting Diodes (HB-LEDs) are considered the future trend in lighting not only due to their high efficiency and high reliability, but also due to their other outstanding chara...

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An Overview of the AC-DC and DC-DC Converters for LED Lighting Applications

This article presents an overview of technologies for solid-state lighting (SSL). In recent years, light-emitting diodes (LEDs) have developed characteristics desirable for lighting applications. The success of these light sources for general lighting depends on the system design, which comprises an understanding of electrical and photometrical characteristics under the temperature effect on device performance. This review focuses on the main theoretical models for the characterization of SSL devices, regarding the electrical and thermal aspects to reach the desired photometrical characteristic for a lighting system. An approach about inorganic LEDs and organic LEDs (OLEDs) will be presented along with the application of these devices in SSL systems.

Solid-State Lighting: A Concise Review of the State of the Art on LED and OLED Modeling

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 light-emitting diodes (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, whereas 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 (LFR) of the first converter, thus smoothing the LED current. In this way, the LFR 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. In addition to 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 V
 rms
/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.

Capacitance Reduction With An Optimized Converter Connection Applied to LED Drivers

In this work, a new topology of integrated converter is proposed to be used as an off-line LED driver. The two stages of the converter are made up by a front-end SEPIC power factor corrector and a buck-boost converter for current regulation, both stages sharing the same power switch. It is demonstrated that when both stages work in DCM, less low-frequency ripple is transmitted from the bus capacitor to the output, allowing decreasing the amount of filtering needed and eliminating electrolytic capacitors from the power circuitry. Photometric data is used to size the maximum current ripple permissible at the LEDs, further optimizing filtering requirements and reducing capacitances to the maximum.

Integrated SEPIC buck-boost converter as an off-line LED driver without electrolytic capacitors

This work deals with the analysis and photometric comparison between different systems concepts for public lighting, hence the solid state lighting (SSL) employing LED luminaires with electronic drivers and the conventional high pressure sodium (HPS) lamp based luminaires along with electromagnetic ballasts. The study and comparison raise question on the relative perception of the human eye to different light sources with different spectral distributions, devoting special attention to low luminance conditions (scotopic) such as those present on public roadway lighting. Different LED-based luminaires are tested, in the lab and in loco. Photometric data of a SSL system being currently installed for the replacement of current HPS luminaires at the School of Engineering of the Federal University of Juiz de Fora are provided for the analysis and comparison.

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An experimental comparison between different technologies arising for public lighting: LED luminaires replacing high pressure sodium lamps

This work proposes an off-line LED driver, based on the Cuk converter operating in discontinuous conduction mode. Complete analysis of the converter is carried out and a design methodology is presented, focused in reducing output filtering capacitance, still achieving acceptable current ripple on the output and eliminating the need for electrolytic capacitors. Photometric data is gathered and fed into the design methodology in order to optimize output current ripple selection and capacitor reduction. Experimental results were obtained from a high power factor high efficiency prototype feeding 56 series-associated high-power LEDs from 220 VAC-60 Hz mains.

A single-stage high efficiency long-life off-line LED driver based on the DCM Cuk converter

This paper proposes a very low-cost circuit to drive a multistring LED-based luminaire which can be employed in street lighting. The circuit is based on a DCM buck-boost power factor corrector stage and four simple linear current equalizers which feed four LED strings. Though very simple and employing a linear technique to balance current on the output, the luminaire has a fair efficiency at full power, with high input power factor and very low input current distortion. Experimental results with a 176 W prototype are presented to validate the concept.

Proposal of a low-cost LED driver for a multistring street lighting luminaire

This paper focuses on the problem of driving parallel strings of LEDs while ensuring current equalization between them. This issue is addressed in terms of proposing a small and simple linear topology that can be used on a number of series-associated LEDs, working as a constant current source for each string. Such topology employs a four-component circuit, with low dependence on transistor parameters, ensuring easy repeatability and good current regulation. Mathematical description of the circuit and experimental results are provided.

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Danilo P. Pinto

Papers

Integrated SEPIC buck-boost converter as an off-line LED driver without electrolytic capacitors

An experimental comparison between different technologies arising for public lighting: LED luminaires replacing high pressure sodium lamps

A single-stage high efficiency long-life off-line LED driver based on the DCM Cuk converter

Proposal of a low-cost LED driver for a multistring street lighting luminaire

A novel method of current equalization in LED strings based on simple linear circuit