A review and classification of LED ballasts

This paper presents a review on existing ballasts for light-emitting diodes (LED) with considerations to their compliance to regulations, technological challenges, and on meeting various application requirements. All existing LED ballasts, including those proposed in recent literature, have been appropriately classified and systematically organized for the discussion. The dissemination of this information and its understanding is helpful for future R&D pursuits in this area. © 2013 IEEE.published_or_final_versio

A Survey, Classification and Critical Review of Light-Emitting Diode Drivers

Based on a survey on over 1400 commercial LED drivers and a literature review, a range of LED driver topologies are classified according to their applications, power ratings, performance and their energy storage and regulatory requirements. Both passive and active LED drivers are included in the review and their advantages and disadvantages are discussed. This paper also presents an overall view on the technical and cost aspects of the LED technology, which is useful to both researchers and engineers in the lighting industry. Some general guidelines for selecting driver topologies are included to aid design engineers to make appropriate choices.published_or_final_versio

A Comprehensive Review on Recent Developments of LED Drivers

Background: In these recent years, LED lighting has been widely implemented for household and industrial applications. By implementing the correct topology, the performance of a LED driver can be improved in terms of efficiency, power factor, lifespan, size and cost of development. Objective: This paper aims to provide a comprehensive review on the latest trends of LED driver design to serve as a useful guide for design engineers and researchers. Result: Latest research journals and conference proceedings have been reviewed. Conclusion: There are suitable converter topologies for LED drivers of varied power levels, with the flyback converter being the most suitable for applications of less than 100W. When designing the LED driver, considerations must be made on the power factor, efficiency, dimming capability, and lifespan

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

Techniques to Improve LED Drivers by Reducing Voltage Stress and Energy Storage

High-brightness light-emitting diodes (HB LEDs) provide many advantages over other existing electric light sources, including high efficacy, long lifetime and small form factor. However, the overall lifetime of off-line LED applications is limited by the low-quality electrolytic capacitors utilized for energy storage. In order to use long-life capacitors while limiting cost increase, the required energy-storage capacitance should be reduced, which can be achieved with several techniques addressed in this thesis. The constant input current approach can achieve a power factor (PF) of 0.9, which meets ENERGY STAR requirements, while reducing required energy storage by one-third compared to unity-PF case. When ripple is allowed on the LED current, the trapezoidal LED current approach minimizes energy storage with small control effort. A second stage can significantly reduce required capacitance by allowing large voltage variation on the capacitor, while bidirectional structure helps limit additional power loss. The small form factor of LEDs offers flexibility for diverse and sophisticated design. In order to take this advantage, LED drivers should have a small size or thickness. Series-input structure provides a possibility to apply low-voltage components in high-voltage circuits, while the common duty cycle approach achieves automatic input voltage sharing and LED current copying, which can significantly simplify system design. With reduced rated voltage, integration of semiconductor devices becomes much easier and converters are able to operate at high switching frequencies with small components, both of which lead to high-level monolithic integration. All of the principles and control approaches are verified in experiments, with the results provided in this thesis

Pregled AC-DC i DC-DC pretvarača za primjene u LED rasvjeti

High-Brightness Light Emitting Diodes (HB-LEDs) are considered the future trend in lighting not only due to their high efficiency and high reliability, but also due to their other outstanding characteristics: chromatic variety, shock and vibration resistance, etc. Nevertheless, they need the development of new power supplies especially designed for boosting and taking advantage of their aforementioned characteristics. Besides, their behaviour is completely different from the rest of lighting devices and, consequently, it should be also taken into account in the design of the converters used to drive them. As a result, many well-known topologies have been optimized or redesigned in order to be used in LED–lighting applications and many new topologies have come up in the recent years with the same purpose. In this paper, the main HB-LED characteristics will be explained, highlighting how they influence the design of their power supplies. After, the main topologies will be presented from the simplest to the most complex ones, analysing their advantages and disadvantages.Svjetleće diode s visokom razinom svjetline (HB-LED) smatraju se budućim trendom u rasvjeti zahvaljujući ne samo visokom stupnju efikasnosti i pouzdanosti, nego i njihovim izvanrednim svojstvima: raznolikost boja, otpornost na udarce i vibracije i sl. Ipak, s ciljem potpunog iskorištenja prethodno spomenutih svojstava, potrebno je razviti nove, posebno osmišljene izvore napajanja. Osim toga, ponašanje im se posve razlikuje od ostalih tipova rasvjete što je potrebno uzeti u obzir pri projektiranju pretvarača za njihovo napajanje. Kao posljedica toga, mnoge su poznate topologije pretvarača optimirane ili preoblikovane posebno za primjenu u LED rasvjeti, a zadnjih nekoliko godina mnoge nove su se tek pojavile. U ovom članku objašnjena su osnovna HB-LED svojstva naglašavajući njihov utjecaj na razvoj izvora napajanja. Uz to, prikazane su osnovne topologije, od najjednostavnijih do najsloženijih, ujedno analizirajući prednosti i nedostatke pojedinih

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

Advanced high frequency switched-mode power supply techniques and applications

This Thesis examines the operation and dynamic performance of a single-stage, single-switch power factor corrector, S4 PFC, with an integrated magnetic device, IM. Also detailed isthe development and analysis of a high power light emitting diode, HP LED, power factorcorrection converter and proposed voltage regulation band control approach.The S4 PFC consists of a cascaded discontinuous current mode, DCM, boost stage anda continuous current mode, CCM, forward converter. The S4 PFC achieves a high powerfactor, low input current harmonics and a regulated voltage output, utilising a singleMOSFET. A steady-state analysis of the S4 PFC with the IM is performed, identifying theoperating boundary conditions for the DCM power factor correction stage and the CCMoutput voltage regulation stage. Integrated magnetic analysis focuses on understanding theperformance, operation and generated flux paths within the IM core, ensuring the device doesnot affect the normal operation of the converter power stage. A design method for the S4 PFCwith IM component is developed along with a cost analysis of this approach. Analysis predictsthe performance of the S4 PFC and the IM, and the theoretical work is validated by MATLABand SABER simulations and measurements of a 180 W prototype converter.It is not only the development of new topological approaches that drives theadvancement of power electronic techniques. The recent emergence of HP LEDs has led to aflurry of new application areas for these devices. A DCM buck-boost converter performs thepower factor correction and energy storage, and a cascaded boundary conduction current modebuck converter regulates the current through the LED arrays. To match the useful operatinglifetime of the HP LEDs, electrolytic capacitors are not used in the PFC converter. Analysisexamines the operation and dynamic characteristics of a PFC converter with low capacitiveenergy storage capacity and its implications on the control method. A modified regulationband control approach is proposed to ensure a high power factor, low input current harmonicsand output voltage regulation of the PFC stage. Small signal analysis describes the dynamicperformance of the PFC converter, Circle Criterion is used to determine the loop stability.Theoretical work is validated by SABER and MATLAB simulations and measurements of a180 W prototype street luminaire.EThOS - Electronic Theses Online ServicePSU DesignsDialight LumidrivesGBUnited Kingdo

SMART ELECTRONIC LIGHTING BALLAST APPLICATION FOR SALTWATER ENVIRONMENT

This work is about the design methodology of electronic ballast for saltwater environment application. The effect of environment to electronic devices research stated that electronic circuit exposed to salty environment has high tendency to damage. Therefore, the protection scheme needs to be added to avoid malfunction. The power supply cut-off circuit is the simplest way to protect ballast from damage at the input terminal. All the circuit simulation is performed using NI Multisim circuit simulator. It is found that self oscillating electronic ballast with power supply cut off circuit is the simplest way to protect ballast circuit at saltwater application. By stages, an electronic ballast circuit is simulated and the output waveform is observed. Start with bridge rectifier, which is produce smooth DC voltage. Then follow by basic ballast circuit. Next, the circuit improved using self oscillating driver. Lastly, electronic ballast circuit combined with power supply circuit

Long Life Single Stage PFC/SLC Converter driving LEDs

Licht emittierende Dioden (LEDs) sind heutzutage für Beleuchtungsanwendungen Stand der Technik und daher allgegenwärtig. Langlebige Beleuchtungsanwendungen erfordern allerdings ein robustes Systemdesign. Daher wurde die typische Ausfallursache von LED-Leuchten ermittelt: Die Stromversorgung ist mit 52% die wahrscheinlichste Ausfallursache. In manchen Anwendungen muss der LED Treiber theoretisch zehn Mal ausgetauscht werden, bevor die Lebensdauergrenze des LED-Moduls erreicht wird. Diese Arbeit beschäftigt sich daher mit der Entwicklung eines langlebigen, einstufigen LED Treibers, welcher aus einer Leistungsfaktorkorrektur (PFC) und einem Serien LC (SLC) Wandler besteht. Ein Großteil der Ausfälle des LED-Treibers wird dabei durch den Elektrolytkondensator verursacht. Durch den Ersatz des Elektrolytkondensators durch einen Filmkondensator wird prognostiziert, dass die Lebensdauer der Leuchte deutlich erhöht werden kann. Im Abschnitt 4 werden verschiedene LED-Treibertechnologien und Topologien analysiert. Nach einer ganzheitlichen Topologieanalyse wurde die PFC/SLC-Topologie gewählt. Die dabei verwendete diskontinuierliche totem pole Leistungsfaktorkorrektur (PFC) und der Serien LC Wandler wurden im Zeitbereich analysiert. Für beide Wandler wird der durchschnittliche Eingangsstrom bzw. der durchschnittliche Ausgangsstrom bestimmt. Da zwei Stellgrößen gleichzeitig eingestellt werden müssen, der AC-Eingangsstrom und der DC-Ausgangsstrom, sind für die Steuerung zwei Freiheitsgrade erforderlich. Die PFC- und SLC-Übertragungsfunktionen werden jeweils durch Frequenz und Tastgrad gesteuert. Dazu wurde eine Lösungsfunktion entwickelt, welche die Frequenz und den Tastgrad in Abhängigkeit von Eingangsleitwert, Ausgangsstrom und mehreren Messwerten berechnet. Durch die Erfassung der Zwischenkreisspannung und der Ausgangsspannung wirken sich deren Änderungen nur minimal auf den Ausgangsstrom aus. Dies erlaubt einen höheren Spannungsripple am Zwischenkreiskondensator, und damit den Ersatz von Elektrolytkondensatoren durch Folienkondensatoren. Die Lebensdauer des LED-Treibers wird dadurch deutlich steigert. Für den verwendeten Regelalgorithmus müssen mehrere Spannungen und Ströme gleichzeitig gemessen und digital gefiltert werden. Beispielsweise wird die Zwischenkreisspannung zuerst analog gefiltert, dann AD gewandelt und erneut digital durch einen resonanten Beobachter gefiltert. So kann die doppelte Netzfrequenz im Zwischenkreiskondensator herausgefiltert werden. Weiterhin wird ein Verfahren zur galvanisch getrennten Spannungsmessung entwickelt. Dadurch kann die Steuerung auf der Primärseite platziert werden, während die Sekundärseite genau gemessen werden kann. Auf Grundlage der vorgeschlagenen Messschaltung werden Schutzkonzepte entwickelt, um eine Selbstzerstörung oder Schädigung während des Betriebs vorzubeugen. Um die Anzahl der LEDs in einem LED-Modules zu erhöhen, z. B. um kleinere MidPower-LEDs anstelle von HighPower-LEDs einzusetzen, wird eine neuartige Parallelschaltungskonzept für LEDs entwickelt. Die Schaltung misst die einzelnen Strangströme, bildet dann einen Mittelwert aus den einzelnen Strangströmen, welcher wiederum dann als Vorgabewert genutzt wird. Auf diese Weise können LEDs sicher, und ohne Beeinträchtigung der Effizienz und Lebensdauer parallel geschaltet werden. Für den Betrieb des LED-Treibers wird ein ausgeklügeltes Hilfsspannungskonzept zur Selbstversorgung entwickelt. Da die Regelung digital implementiert ist, ist ein tiefgreifendes Softwareengineering erforderlich, um die Echtzeitperformance der CPU sicherzustellen. Eine unzureichende Implementierung der Regelungssoftware führt zu einem instabilen Regelkreis. Die Messungen am Ende der Arbeit zeigen, dass ein langlebiger, flimmerfreier LED-Treiber entwickelt wurde. Der Netzeingangsstrom ist dabei sinusförmig, während der LED Ausgangsstrom nahezu konstant ist. Der maximale Wirkungsgrad des LED-Treibers wurde zu 93% bestimmt