Novel Offline Switched Mode Power Supplies for Solid State Lighting Applications

In recent years, high brightness light emitting diodes (HBLEDs) have increasingly attracted the interest of both industrial manufacturers and academic research community. Among the several aspects that make LED technology so attractive, the most appreciated characteristics are related to their robustness, high efficiency, small size, easy dimming capability, long lifetime, very short switch-on/switch-off times and mercury free manufacturing. Even if all such qualities would seem to give to solid state lighting a clear advantage over all the other kinds of competing technologies, the issues deriving from the need of LED technology improvement, on one hand, and of the development of suitable electronic ballasts to properly drive such solid state light sources, on the other, have so far hindered the expected practical applications. The latter problem, in particular, is nowadays considered the main bottleneck in view of a widespread diffusion of solid state technology in the general lighting market, as a suitable replacement of the still dominant solutions, namely halogen and fluorescent lamps. In fact, if it is true that some aspects of the devices’ technology (e.g. temperature dependent performance, light quality, efficiency droop, high price per lumen, etc…) still need further improvements, it is now generally recognized that one of the key requirements, for a large scale spread of solid state lighting, is the optimization of the driver. In particular, the most important specifications for a LED lamp ballast are: high reliability and efficiency, high power factor, output current regulation, dimming capability, low cost and volume minimization (especially in domestic general lighting applications). From this standpoint, the main goal is, therefore, to find out simple switched mode power converter topologies, characterized by reduced component count and low current/voltage stresses, that avoid the use of short lifetime devices like electrolytic capacitors. Moreover, if compactness is a major issue, also soft switching capability becomes mandatory, in order to enable volume minimization of the reactive components by increasing the switching frequency in the range of the hundreds of kHz without significantly affecting converter’s efficiency. It is worth mentioning that, in order to optimize HBLED operation, also other matters, like the lamp thermal management concern, should be properly addressed in order to minimize the stress suffered by the light emitting devices and, consequently, the deterioration of the light quality and of the expected lamp lifetime. However, being this work focused on the issues related to the research of innovative driving solutions, the aforementioned thermal management problems, as also all the topics related to the improvement of solid state devices’ technology, will be left aside. The main goal of the work presented in this thesis is, indeed, to find out, analyze and optimize new suitable topologies, capable of matching the previously described specifications and also of successfully facing the many challenges dictated by the future of general lighting. First of all, a general overview of solid state lighting features, of the state of the art of lighting market and of the main LED driving issues will be provided. After this first introduction, the offline driving concern will be extensively discussed and different ways of approaching the problem, depending on the specific application considered, will be described. The first kind of approach investigated is based on the use of a simple structure relying on a single power conversion stage, capable of concurrently ensuring: compliance with the standards limiting the input current harmonics, regulation of the load current and also galvanic isolation. The constraints deriving from the need to fulfil the EN 61000-3-2 harmonics standard requirements, when using such kind of solution for low power (<15W) LED driving purposes, will be extensively discussed. A low cost, low component count, high switching frequency converter, based on the asymmetrical half bridge flyback topology, has been studied, developed and optimized. The simplicity and high compactness, characterizing this solution, make it a very good option for CFL and bulb replacement applications, in which volume minimization is mandatory in order to reach the goal of placing the whole driving circuitry in the standard E27 sockets. The analysis performed will be presented, together with the design procedure, the simulation outcomes and the different control and optimization techniques that were studied, implemented and tested on the converter's laboratory prototype. Another interesting approach, that will be considered, is based on the use of integrated topologies in which two different power conversion stages are merged by sharing the same power switch and control circuitry. In the resulting converter, power factor correction and LED current regulation are thus performed by two combined semi-stages in which both the input power and the output current have to be managed by the same shared switch. Compared with a conventional two-stages configuration, lower circuit complexity and cost, reduced component count and higher compactness can be achieved through integration, at cost of increased stress levels on the power switch and of losing a degree of freedom in converter design. Galvanic isolation can be provided or not depending on the topologies selected for integration. If non-isolated topologies are considered for both semi-stages, the user safety has to be guaranteed by assuring mechanical isolation throughout the LED lamp case. The issue, deriving from the need of smoothing the pulsating power absorbed from the line while avoiding the use of short lifetime electrolytic capacitors, will be addressed. A set of integrated topologies, used as HBLED lamp power supplies, will be investigated and a generalized analysis will be presented. Their input line voltage ripple attenuation capability will be examined and a general design procedure will be described. Moreover, a novel integrated solution, based on the use of a double buck converter, for an about 15W rated down-lighting application will be presented. The analysis performed, together with converter design and power factor correction concerns will be carefully discussed and the main outcomes of the tests performed at simulation level will be provided. The last kind of approach to be discussed is based on a multi-stage structure that results to be a suitable option for medium power applications, like street lighting, in which compactness is not a major concern. By adopting such kind of solution it is, indeed, possible to optimize converter’s behavior both on line and on load side, thereby guaranteeing both an effective power factor correction at the input and proper current regulation and dimming capability at the output. Galvanic isolation can be provided either by the input or the output stage, resulting in a standard two stage configuration, or by an additional intermediate isolated DC-DC stage (operating in open loop with a constant input/output voltage conversion ratio) that namely turns the AC/DC converter topology into a three stage configuration. The efficiency issue, deriving from the need of multiple energy processing along the path between the utility grid and the LED load, can be effectively addressed thanks to the high flexibility guaranteed by this structure that, relaxing the design constraint, allows to easily optimize each stage. A 150W nominal power rated ballast for street solid state lighting applications, based on the latter (three stage) topology, has been investigated. The analysis performed, the design procedure and the simulations outcomes will be carefully described, as well as the experimental results of the tests made on the implemented laboratory prototype

2014 Projects Day Booklet

https://scholarworks.seattleu.edu/projects-day/1029/thumbnail.jp

A Novel Boost Converter Based LED Driver Chip Targeting Mobile Applications

abstract: A novel integrated constant current LED driver design on a single chip is developed in this dissertation. The entire design consists of two sections. The first section is a DC-DC switching regulator (boost regulator) as the frontend power supply; the second section is the constant current LED driver system. In the first section, a pulse width modulated (PWM) peak current mode boost regulator is utilized. The overall boost regulator system and its related sub-cells are explained. Among them, an original error amplifier design, a current sensing circuit and slope compensation circuit are presented. In the second section – the focus of this dissertation – a highly accurate constant current LED driver system design is unveiled. The detailed description of this highly accurate LED driver system and its related sub-cells are presented. A hybrid PWM and linear current modulation scheme to adjust the LED driver output currents is explained. The novel design ideas to improve the LED current accuracy and channel-to-channel output current mismatch are also explained in detail. These ideas include a novel LED driver system architecture utilizing 1) a dynamic current mirror structure and 2) a closed loop structure to keep the feedback loop of the LED driver active all the time during both PWM on-duty and PWM off-duty periods. Inside the LED driver structure, the driving amplifier with a novel slew rate enhancement circuit to dramatically accelerate its response time is also presented.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

A comprehensive review on various non-isolated power converter topologies for a light-emitting diode driver

Light-emitting diode (LED) lighting applications aided by an electronic power control have become very attractive in the recent years. For LED lighting applications, it is essential to design a converter with single/multi-output for handling multiple loads. As the LED load is more sensitive to the change in input/converter parameters, it is necessary to regulate the current concerning the design specifications. In this paper, several LED topologies are reviewed with a focus on power density, single/multi-load operation, size, and reliability. Several converter topologies are reviewed and compared in terms of power rating, number of semiconductor switches, isolation, and efficiency. Various modulation techniques used for dimming control are described in brief. The salient features of each converter topology are discussed with the power rating and application for which the topology can be preferred. So, the selection of the power factor correction (PFC) and low source side harmonics converter topology is presented. This paper will be helpful to the researchers who are working on the development of LED drivers

Design of car tunnel lighting

Based on the analysis of the international standards of lighting of motor transport tunnels the generalization of the basic directions of increase of economy, safety and comfort of lighting is carried out. The normative indicators of illumination and brightness in different zones of the tunnel depending on its parameters and characteristics of road traffic taking into account features of light adaptation of a human eye are systematized. Different types of lighting of motor tunnels depending on the purpose of lighting, location of lighting fixtures, direction and intensity of road traffic are analyzed. Based on the analysis of lighting and electrical parameters of light sources, the expediency of their use for different types of tunnel lighting is substantiated.На основі аналізу міжнародних стандартів освітлення автотранспортних тунелів проведено узагальнення основних напрямків підвищення економічності, безпечності та комфортності освітлення, систематизовано нормативні показники освітленості та яскравості в різних зонах тунелю в залежності від його параметрів і характеристик дорожнього руху з врахуванням особливостей світлової адаптації ока людини. Проаналізовано різні види освітлення автотранспортних тунелів залежно від призначення освітлення, розміщення світлових приладів, напрямку та інтенсивності руху автомобільного транспорту. На основі аналізу світлотехнічних та електричних параметрів джерел світла обґрунтовано доцільність їх використання для різних видів освітлення тунелю. Проведено порівняння характеристик світлових приладів з розрядними і напівпровідниковими джерелами світла. Розглянуто можливість ступінчатого та плавного регулювання освітленості тунелю в нічний час доби. Обгрунтовано доцільність застосування ступінчатого регулювання освітленості при використанні розрядних джерел світла та можливість плавного і ступінчатого регулювання освітленості при використанні напівпровідникових джерел світла. Розроблено схему освітлення автотранспортного тунелю з врахуванням особливостей світлової адаптації ока людини при різних параметрах тунелю, інтенсивності автомобільного руху, часу доби.Based on the analysis of the international standards of lighting of motor transport tunnels the generalization of the basic directions of increase of economy, safety and comfort of lighting is carried out. The normative indicators of illumination and brightness in different zones of the tunnel depending on its parameters and characteristics of road traffic taking into account features of light adaptation of a human eye are systematized. Different types of lighting of motor tunnels depending on the purpose of lighting, location of lighting fixtures, direction and intensity of road traffic are analyzed. Based on the analysis of lighting and electrical parameters of light sources, the expediency of their use for different types of tunnel lighting is substantiated. The characteristics of luminaires with discharge lamps of high pressure and LED are compared. Methods of light regulation in tunnels are analyzed, their advantages and disadvantages are established, recommendations on use for different types of lighting installations are given. The scheme of illumination of the motor transport tunnel is developed taking into account features of light adaptation of a human eye at various parameters of the tunnel, intensity of automobile traffic, time of day.INTRODUCTION 6 1 ANALYTICAL SECTION 8 1.1 Types of road tunnels and it’s relation with the lighting requirements and their characteristics 8 1.2 Ways to increase the efficiency of lighting tunnels 23 1.3 Conclusions to section 1 26 2 CALCULATION AND RESEARCH SECTION 27 2.1 Lighting devices for road tunnels 27 2.2 Placement of luminaires in tunnels 35 2.3 Methods of light control 37 2.3.1 Stepwise adjustment of the light level 38 2.3.2 Smooth adjustment of light level 40 2.4 Conclusions to section 2 47 3 PROJECT DESIGNING SECTION 48 3.1. Lighting calculation of a lighting installation for a transport tunnel 48 3.2. Adjusting the luminous flux of the lighting installation 60 3.3 Comparison of energy efficiency of the developed lighting installations 61 3.4 Conclusions to section 3 64 4 LABOUR OCCUPATIONAL SAFETY AND SECURITY IN EMERGENCY SITUATIONS 66 4.1. Safety requirements for the installation of lighting fixtures 66 4.2. The effect of electric current on humans. First aid for electric injuries 67 4.3 Influence of electromagnetic fields on the human body 70 GENERAL CONCLUSIONS FOR QUALIFICATION WORK 73 REFRENCES 7