Danilo P. Pinto

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

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.

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

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.

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

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.

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

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

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.

A comparative study between two single-stage LED drivers: A sole converter versus an integrated topology

This work proposes a comparison between two different approaches for LED driving, based on the Ćuk converter operating in discontinuous conduction mode and an integrated SEPIC Buck-Boost converter. A brief analysis of each 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. The LED photometric performance under different ripple conditions has been analyzed to aid the design methodology in order to optimize output current ripple selection and capacitor reduction. The control strategy for each converter was presented and validated experimentally. Experimental results were obtained for both converters from two prototypes feeding 56 series-associated high-power LEDs from 220 VAC-60 Hz mains.

Experimental characterization regarding two types of phosphor-converted white high-brightness LEDs: Low power and high power devices

This paper describes an experimental photometrical analysis regarding two mainstreams inside the high-brightness LED family: the power devices, socalled high power LEDs, and the low power devices. Focus is given to white phosphor-converted LEDs, which are used in LED-based luminaires for indoor and outdoor lighting. Data from several LEDs used in available luminaires are compiled and provided as photometrical references for the design considerations in light output of LED drivers which employ power electronic converters.

The Discipline and the Energy Efficiency Laboratory (LEENER): Formation, Development and Transference of Technology for the Combat to the Energy Waste

This paper describes the main issues concerning the creation of the discipline and the new laboratory of Energy Efficiency, recently introduced in the Electrical Engineering curriculum at Federal University of Juiz de Fora. The conception, the establishment and results reporting are well documented and detailed. The pedagogical bases for the development of the subject are also explained, stressing the importance of including energy saving contents and awareness about energy wastefulness in the generic engineering curricula. Human and technological axes are both considered in the scope of this work. It is possible to conclude that, after subject completion, the students develop competence and improve skills to accomplish a number of energy saving projects, being able to propose actions or modifications intended to reduce the energy account and to provide installation compliance with standards. Those directions can certainly result in processes efficiency and modernization, since they are grounded on the use of up to date equipments and competitive techniques. By this way, the new engineers can play an important role in our power dependent world since they are able to disseminate a new and very opportune culture: the fight against electrical energy wastefulness.

Street lighting LED luminaires replacing high pressure sodium lamps: Study of case

This paper deals with the study of the pilot project of street lighting using LED luminaires on the campus of Federal University of Juiz de Fora. Over twenty nine months the system was monitored in order to evaluate the performance of this technology that is gaining ground in the lighting industry. Photometric and electrical results obtained during this period will be presented as well as a comparison with the old lighting system that employs high-pressure sodium lamps based on classical photometry and mesopic photometry, which takes into account the dynamic visual response of the human eye. In addition, will be done a simplified economic analysis aiming to show the saving generated by the new lighting system and a calculation of payback of the new luminaires.

Um estudo comparativo de sistemas de iluminação pública: Estado sólido e lâmpadas de vapor de sódio em alta pressão

This work deals with the viability analysis and photometric comparison between two different systems concepts for public lighting, hence the solid state lighting (SSL) employing high power LED luminaries with integrated electronic converters and the conventional high pressure sodium (HPS) lamp based luminaries along with electromagnetic ballasts. The study and comparison stem on the relative perception of the human eye to different light sources with different spectral distributions, devoting special attention to scotopic conditions of illumination. Photometric data of a SSL system being currently installed for the replacement of current HPS luminaries at the School of Engineering of the Federal University of Juiz de Fora is provided for the analysis and comparison.