LED LIGHTING AND DRIVERS

The book is organized in four chapters. Chapter 1 deals with an introduction to light and lighting. As a power electronics engineer working on LEDs and lighting systems in general, I think it is important for the reader to have the basic knowledge about lighting systems, which I have tried to summarize in this chapter. Because of the extremely interesting possibilities of LEDs to generate different light colors, Chapter 1 includes a section related to the understanding of color quantification and measurement in different color spaces. The Chapter also includes several examples on light and color calculations.In order to develop and implement a suitable LED driver, it is necessary to have a good knowledge about LED behavior and characteristics. Thus, Chapter 2 aims at providing the reader with the most important issues related to LED operation and modeling from a practical point of view. The most common LED structures and materials are presented in this chapter together with the most relevant electrical, thermal and optical characteristics, making special emphasis on those characteristics provided by LED manufacturers in their datasheets. Special sections are dedicated to light dimming and color mixing. The chapter is closed with a brief review of organic LED (OLED) technology, which is another promising LED technology nowadays.Chapter 3 is devoted to DC LED drivers, which are those LED drivers intended to supply the LED from a DC voltage source, like a battery or a DC bus. This chapter covers the three most relevant technologies that are being used to implement DC LED drivers at the present time, which are those based on linear regulators, switched capacitor regulators and switching regulators. The most relevant solutions to implement DC LED drivers are reviewed from a practical point of view. The chapter also reviews the most common control methods applied to DC LED drivers. Examples are included by means of computer simulations based on LTspice, which is a free but powerful SPICE-based simulation software developed by former Linear Technologies Company, now part of Analog Devices. The chapter ends with a section devoted to LED configurations, namely, series, parallel and matrix configurations, which are employed to implement high-power LED lamps.Finally, Chapter 4 is dedicated to off-line LED drivers. This is the denomination given to LED drivers that are intended to operate from an AC grid voltage. These are the most complicated LED drivers since they usually require the implementation of a front-end power-factor-correction (PFC) stage followed by a downstream DC-DC converter to adapt voltage levels and provide regulated current to the LED lamp. The most important standards and regulations related to this type of LED drivers are presented at the beginning of the chapter. Then, single-stage LED drivers are studied, which can be used as a stand-alone off-line LED driver or as a first stage in a two-stage off-line LED driver. The highly-relevant problem of requiring a large storage capacitance in single-stage off-line LED drivers to cope with the double-line-frequency pulsating power originated from line voltage rectification is addressed in this chapter. Finally, integrated two-stage off-line LED drivers are presented and studied as a solution to reduce the storage capacitance of off-line LED drivers, aiming at using high-reliability film-capacitors instead of less reliable electrolytic capacitors. LTspice simulation examples are also provided in this chapter to allow the reader to have a better idea about the design and operation of this type of LED drivers. Read more