Pedro S. Almeida

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.

Offline Soft-Switched LED Driver Based on an Integrated Bridgeless Boost–Asymmetrical Half-Bridge Converter

This paper proposes an offline single-stage light-emitting diode (LED) driver based on a novel approach to reduce low-frequency ripple in LED arrays supplied from mains, while assuring high input power factor (PF). The proposal employs a series resonant dc-dc converter integrated into a bridgeless boost power factor correction (PFC) stage. The resonant stage works to reduce the low-frequency ripple transmitted from the output of the PFC stage to the LEDs with only small power losses. This solution achieves three main goals: 1) reduction of the bulk capacitance used at the dc bus, allowing for the use of long-life film capacitors; 2) increase in the overall efficiency of the LED driver owing to the low switching and conduction losses in the shared switching network; and 3) assuring high input PF. Experimental results of a driver without electrolytic capacitors for a 100-W street lighting LED luminaire are presented, showing overall efficiency in excess of 92%, input PF greater than 0.97, and line current harmonic content in compliance with the IEC 61000-3-2 standard.

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.

An experimental study on the photometrical impacts of several current waveforms on power white LEDs

Since light-emitting diodes (LEDs) are a rising lighting technology, a great amount of research is currently being focused on driving techniques for these current-fed semiconductor devices. For realizing efficient current drivers, power electronics is usually employed. This work focuses on studying the impacts that several high and low frequency current waveforms commonly found on power electronic drivers may have on the photometrical and colorimetrical performance of the LEDs themselves. Empirical evidence obtained under controlled experiments is provided to correlate important features of the LEDs to the current levels and waveforms.

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.

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.