An Overview of the AC-DC and DC-DC Converters for LED Lighting Applications

Abstract

Original scientific paperHigh-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. Key words: AC-DC converters, DC-DC converters, LED, LightingPregled AC-DC i DC-DC pretvarača za primjene u LED rasvjeti. 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 ovomčlanku 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.

Digital Implementation of the Feedforward Loop of the Asymmetrical Half-Bridge Converter for LED Lighting Applications

“…Hence, considering (1), (2) and that n 1 and n 2 are designed according to nominal conditions (D nom , V O_nom and V in_nom ), (3) can be used for obtaining the required duty cycle that keeps the output voltage constant:…”

High frequency dc-dc AC-LED driver based on ZCS-QRCs

“…However, HB-LEDs are diodes, which means that the current is able to go through them in only one direction. This feature has made the driving of HB-LEDs from the mains an important research topic for a wide range of power [1]. For this reason, it is required the use of an ac-dc converter, specifically for output powers higher than 25 W it needs to be able to achieve Power Factor Correction (PFC), that feeds the string of HB-LEDs with either a constant [2] or a low-frequency pulsed current in the range of hundreds to thousands of kHz [3].…”

On Supplying LEDs From Very Low DC Voltages With High-Frequency AC-LED Drivers

“…It is a well-known fact, that LEDs can only be driven by forward currents, since they behave as a diode allowing the current to flow in one direction only. This fact has made the driving of LEDs from AC grids a main research topic to replace old inefficient luminaries [1], [2]. In fact, if the current source is not acceptable for the driving of the luminaire a dc-dc converter needs to adapt the level of current to drive them accurately.…”