Guilherme M. Soares

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.

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.

Off-line flyback LED driver with PWM dimming and power factor correction employing a single switch

In this work, an off-line flyback converter with PWM dimming function employing a single active power switch is proposed for LED lighting. The proposed converter is a slightly modified flyback topology which enables the main switch to be used both for power factor correction and PWM high-frequency dimming with a constant peak current on the LEDs, in order to conserve chromatic characteristics of the light emitted. The proposed control scheme uses duty-cycle to control the dimming level, while switching frequency is varied along to adjust the input power level and maintain a constant peak current on the LEDs. Mathematical description, simulation and experimental results of a prototype with 100 W of peak power fed from 127 V mains voltage are presented in this paper to show feasibility of the single-stage converter proposal.

Smart modules for lighting system applications and power quality measurements

Smart lighting applications are designed to provide management and control of the whole interconnected system, ensuring reliability, cost saving and high efficiency. In this work is proposed a simple intelligent module to be connected in the street lighting system in order to simultaneously control and measure the lamps parameters. All the data transmission procedure was developed based on the mesh network topology. By taking advantage of the communication structure used for the smart lighting system and coupling sensors to the module, its possible to gather data regarding the power grid as well. Moreover, for experiments purposes, it was also developed a specific driver capable to communicate by DALI protocol in order to receive and send information from the smart module to the lamp. The results have proven the efficiency, flexibility and interoperability of the proposed smart device.

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.

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.

DCM Integrated Double Buck-Boost led driver with reduced storage capacitance

This work proposes an approach for low frequency current ripple minimization in off-line light-emitting diode (LED) drivers. This strategy is based on the large signal modulation of the duty cycle of a LED converter so that the output ripple can be reduced and, consequently, the required filtering capacitances of the converter can be further decreased. The approach presented in this work is developed by defining a modulation function that allows for a reduction in the storage capacitance, and by analyzing the converter behavior when such function is applied to the driver. The design of the low-frequency filtering element of the converter is performed by using a graphical technique, which allows the designer to evaluate the behavior of the output current ripple and the input current distortion. The analysis is carried out for an Integrated Double Buck-Boost converter and experimental results are shown in order to demonstrate the validity of the proposal.