This thesis presents an investigation into the characteristics of and driving methods for light emitting diode (LED) lamp system. A comprehensive overview on the lighting development is proposed. The characteristic of the light emitting diode (LED) lamp is described and the requirements of the ballast for the light emitting diode (LED) lamp are presented. Although LED lamps have longer lifetime than fluorescent lamps, the short lifetime limitation of LED driver imposed by electrolytic capacitor has to be resolved. Therefore, an LED driver without electrolytic capacitor in the whole power conversion process is preferred. In this thesis, a single phase, power factor correction converter without electrolytic capacitors for LED lighting applications is proposed, which is a modified SEPIC converter working in discontinuous conduction mode (DCM). Different with a conventional SEPIC converter, the middle capacitor is replaced with a valley-fill circuit. The valley-fill circuit could reduce the voltage stress of output diode and middle capacitor under the same power factor condition, thus achieving higher efficiency. Instead of using an electrolytic capacitor for the filter, a polyester capacitor of better lifetime expectancy is used. An interleaved power factor correction SEPIC with valley fill circuit is proposed to further increase the efficiency and to reduce the input and output filter size and cost. The interleaved converter shows the features such as ripple cancellation, good thermal distribution and scalability. / Master of Science

In this work, single stage power factor corrected AC/DC converters for LEDs / single stage Flyback converter having different configuration from the traditional Flyback and single stage SEPIC converter is investigated. The study involves analysis, circuit design, performance comparisons and implementation. The study covers LEDs / their developments, characteristics and state-of-art in this new technology. The circuits are investigated by means of computer simulations. Operating principles and operating modes are studied along with design calculations. After applying prototypes in laboratory, the simulation results and theoretical analyses are confirmed. The single stage Flyback converter has high voltage input (220-240 Vac), and the output feeds up to 216 HB-LEDs, with the ratings of 24 V, 3.25 A with 90 W. The single stage SEPIC converter with universal input (80-265 Vac) has an output that feeds 21 power LEDs, with 67 V, 0.30 and 20 W ratings.

In the design of the state-of-the-art electronic products, power management circuits play a very important role for the enhancement of overall system efficiency. Switched mode DC-DC converter is an increasingly popular power management circuit due to its superior power conversion efficiency. This thesis introduces two efficiency optimization techniques for switched mode power electronic circuits. One is dead-time optimization. This technique can automatically adjust the dead-time on-the-fly according to the circuit operating conditions. Second, an energy conservation based high-efficiency dimmable multi-channel LED driver is discussed. An auxiliary power switched is use to allow free wheeling of the inductor current during the load disconnect period. The sequential burst mode PWM current sharing scheme with dimming capability can effectively reduce design complexity and cost. The proposed LED driver provides a practical solution for the realization of LED BLU in the flat panel TVs with local dimming capability according to the video content.

In the design of the state-of-the-art electronic products, power management circuits play a very important role for the enhancement of overall system efficiency. Switched mode DC-DC converter is an increasingly popular power management circuit due to its superior power conversion efficiency. This thesis introduces two efficiency optimization techniques for switched mode power electronic circuits. One is dead-time optimization. This technique can automatically adjust the dead-time on-the-fly according to the circuit operating conditions. Second, an energy conservation based high-efficiency dimmable multi-channel LED driver is discussed. An auxiliary power switched is use to allow free wheeling of the inductor current during the load disconnect period. The sequential burst mode PWM current sharing scheme with dimming capability can effectively reduce design complexity and cost. The proposed LED driver provides a practical solution for the realization of LED BLU in the flat panel TVs with local dimming capability according to the video content.

Recently, as a promising lighting source, light-emitting diodes (LEDs) have become more and more attractive and have great opportunity to replace traditional lighting sources - incandescent, fluorescent and HID because of the advantages such as high luminous efficacy, long lifetime, quick on/off time, wide color gamut, eco-friendly etc. Based on the research from U.S. Department of Energy, over 30% of total electric consumption in U.S. each year is for lighting, 75% of which are for indoor lighting (including both residential and commercial buildings). In the indoor LED lighting application, to provide multiple current source outputs for multiple LED strings, traditional solutions usually adopt a two-stage structure, which is complicated and cost-ineffective. How to design a simple, low-cost and efficient LED driver with multiple current source outputs is in great demand and really challenging. In this thesis, a single-stage multi-channel constant current (MC3) LED driver structure has been proposed. Multiple transformer structure is utilized to provide multiple current source outputs. The current control scheme is also simple - only one LED string current is sensed and controlled; other strings' currents are cross regulated. Firstly, a PWM half bridge topology is chosen to implement the proposed single-stage MC3 LED driver concept. In order to analyze the current cross regulation, a general model is derived. The circuit has been simulated under various LED load conditions to verify its good current sharing capability. In order to further improve efficiency, simplify the driver's complexity and reduce cost, a LLC resonant topology is also investigated. LLC current gain characteristic has been derived by considering LED's i-v character and a design procedure is developed. A 100 kHz, 200 W, 4-string MC3 LLC LED driver is designed and tested. The experimental results show that the driver can maintain constant current output within the whole input and output variations, achieve good efficiency and realize current sharing under both balanced and unbalanced LED conditions. The dimming function can also be realized through frequency modulation method and burst mode control method. As a conclusion, a single-stage MC3 LED driver concept is proposed and implemented with two topologies. The proposed idea provides a simple, low-cost and efficient solution for indoor LED lighting application with multiple LED string configuration. It also has good current sharing capability and robustness to LED forward voltage variations or short failures. / Master of Science

Cette thèse de doctorat porte sur les fluctuations temporelles du flux lumineux des lampes LED, ce phénomène portant le nom de papilottement (flicker). Le papillotement est habituellement considéré comme une perturbation en raison de son impact négatif sur la santé. Pour les systèmes d'éclairage à base de diodes électroluminescentes (LED), sa définition vient d'être formalisée dans la norme IEEE 1789:2015 et a été décrite pour les appareils alimentés en courant alternatif (CA). Ce papillotement alternatif résulte des interactions entre l'impédance du réseau, l'onde de tension, les courants harmoniques et le convertisseur de courant alternatif en courant continu (CA - CC). L'alimentation en courant continu est généralement obtenue via des convertisseurs à découpage. Par conséquent, les mêmes facteurs perturbateurs sont également présents sur les réseaux à courant continu. Cette thèse résume les diférences entre les propriétés caractéristiques du papillotement sous alimentation en CA et en CC. Il a été montré dans la littérature et aussi dans cette thèse qu'avec les LED, le facteur clé qui affecte le papillotement réside dans la conception du driver de LED - une partie indispensable des systèmes d'éclairage à LED. Cette thèse décrit une méthodologie d'évaluation de la sensibilité au papillotement des lampes LED sous alimentation en CC et analyse la façon dont cette sensibilité se modifie lorsque les drivers de LED sont simplifiés et adaptés à des alimentations CC. La thèse présente un ensemble d'expériences de mesure visant à déterminer la réaction typique du papillotement des lampes LED à la fois sous alimentation CA et CC. D'autres expériences ont été efectuées pour révéler l'impact de l'adaptation du driver à l'alimentation CC (en enlevant le pont redresseur à diodes). On constate que certaines lampes présentent une meilleure résistance au papillotement, tandis que d'autres lampes présentent une moindre résistance. Ces expériences sont accompagnées de simulations de drivers pour les lampes LED visant à reproduire et à expliquer les résultats des mesures. La thèse décrit en outre une expérience de mesure visant à montrer la sévérité typique de la variation de tension dans un réseau CC à basse tension couplé au CA domestique et son impact sur le papillotement. On conclut qu'un tel système est suisamment robuste pour filtrer les perturbations provenant du CA, mais une interaction indésirable entre la lampe et l'alimentation peut se produire. / This dissertation thesis is concerned with temporal fluctuations of the luminous flux of LED lamps, a phenomenon referred to as flicker. Flicker is usually regarded as a disturbance due to its negative impact on human health. For lighting systems based on light emitting diodes (LED), its definition has recently been formalised in norm IEEE 1789-2015 and has been documented on devices supplied with AC voltage. AC flicker results from interactions between network impedance, voltage and current harmonics, and the AC to DC converter. DC supplies are generally obtained by switching converters. Consequently, the same perturbing factors are present on DC networks. The thesis summarises the differences between the characteristic properties of flicker under AC and DC supplies. It has been shown in the literature and also in this thesis that the key factor affecting flicker with LEDs is the design of the LED driver-a necessary part of the LED lighting systems. This thesis describes a methodology for the evaluation of the flicker sensitivity of DC supplied LED lamps and analyses how the sensitivity changes when the LED drivers are simplified and accustomed to DC supply. The thesis presents a set of measurement experiments aimed to determine the typical flicker response of LED lamps both under AC and DC supply. Further experiments were performed to reveal the impact of accustomising the driver to the DC supply (removing the diode rectifier). It was found that some lamps show better flicker immunity while other lamps show worse flicker immunity. These experiments are accompanied by LED driver simulations aiming to reproduce and explain the measurement results. The thesis further describes a measurement experiment aimed to show the typical severity of the voltage fluctuation in a low voltage DC network coupled to AC mains and its impact on the flicker. It is concluded that such a system is robust enough to filter out any perturbations coming from the AC supply, but an undesired interaction between the lamp and the supply may occur.

This master's thesis deals with a design and realization of a LED driver that is based on integrated circuits NCV78703 and NCV78723 from ON Semiconductor. The aim of the project is to create a demonstration application with these integrated circuits for the use of company. The circuits can be especially used for driving LED automotive lights. The driver is controlled with a microcontroller also providing a communication with a software running on a PC via USB interface. This software enables to simply modify parameters of the driver in order to adjust an intensity of LEDs.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work presents an analysis and design of two Light Emitting Diode (LED) drivers topologies based on static switched converters aiming to avoid using electrolytic capacitors. Considering the low lifetime of electrolytic capacitors compared to LEDs, the topologies aims for reducing the storage capacitance and replaces it by a longer lifetime capacitor, increasing the overall system life span. A Proportional Integral controller is designed to reduce the output current ripple. Consequently, it reduces the bus voltage ripple which allows working with reduced bus capacitances. The input current harmonic distortion limit must be observed. The power factor correction stage is based on a Single Ended Primary Inductance Converter (SEPIC) operating under discontinuous conduction mode (MCD) for both topologies. The power control (PC) stage is performed by a Buck converter for the SEPIC-Buck topology and by a Ćuk converter for the SEPIC-Ćuk topology. These PC converters present output current source behavior, suitable for LED application. Two LED driver prototypes are implemented and the results present high efficiency and a 50% current ripple on the LED. Furthermore a simple dimming strategy is proposed and implemented. / Este trabalho apresenta uma análise e projeto para duas topologias de circuito de acionamento para Diodos Emissores de Luz (LED) utilizando conversores estáticos integrados com o objetivo de evitar a utilização de capacitores eletrolíticos. Considerando a baixa vida útil dos capacitores eletrolíticos, se comparada à dos LEDs, as topologias buscam reduzir a capacitância de barramento tornando possível a utilização de capacitores de maior vida útil, aumentando a vida útil do sistema como um todo. Um controlador Proporcional Integral é projetado para reduzir a ondulação na corrente de saída. Consequentemente, a ondulação da tensão de barramento é reduzida permitindo o uso de capacitâncias de barramento reduzidas. O limite da distorção harmônica da corrente de entrada deve ser observado. O estágio de correção do fator de potência é baseado no Conversor com Indutância Simples no Primário (SEPIC) operando no modo de condução descontínuo (MCD) para ambas as topologias. O estágio de controle de potência (PC) é realizado por um conversor Buck para a topologia SEPIC-Buck e por um conversor Ćuk para a topologia SEPIC-Ćuk. Os conversores do estágio PC apresentam característica de fonte de corrente na saída, conveniente para a utilização de LEDs. Dois protótipos para circuitos de acionamento para LEDs são implementados e os resultados apresentam alta eficiência e uma ondulação de 50% na corrente dos LEDs. Além disso, um circuito de controle da intensidade luminosa de bastante simplicidade é proposto e implementado.

Digitally controlled switching DC-DC converters have recently emerged as an attractive alternative to conventional switching converters based on analog control techniques. This research focuses on eliminating the issues associated with the state of the art switching converters by proposing three novel control techniques: (1) a digitally controlled Buck-Boost converter uses a fully synthesized constant ON/OFF time-based fractional-N controller to regulate the output over a 3.3V-to-5.5V input voltage range and provides seamless transition from buck to buck-boost modes (2) a hysteretic buck converter that employs a highly digital hybrid voltage/current mode control to regulate output voltage and switching frequency independently (3) a 10MHz continuous time PID controller using time based signal processing which alleviates the speed limitations associated with conventional analog and digital. All the three techniques employ digitally assisted control techniques and require no external compensation thus making the controllers fully integrated and highly cost effective. / Graduation date: 2013 / Access restricted to the OSU Community at author's request from June 25, 2012 - June 25, 2014

Problems in swithing converter and power losses in this circuit describe these master’s theses. Power losses have the primar influence on the total effectivity circuit. The first chapter deal swith principle of basic parts switching converter (buck, boost, buck-boost). The power losses on main elements used in switching circuit (diode, transistor) are explained in the next part this thesis. Theory of synchronous rectifiction for reduction of losses. A choice of two integrated circuit useful for future design of LED driver working in buck-boost mode is on the end of the theoretical part. The practical part is fosud on the design of circuits (with integrated circuits chose in the theoretical part) including schematic diagram, calculation of parts and PCB layout. The build samples are evaluated by set of measurements in the field of effeciency, temperatures of components, stability output LED current, EMC and soon. Finally the particular parameters of both tested circuits are compared