Preface

Welcome to the second edition of Power Supplies for LED Driving! As in the first edition, the worked examples in this book are based on Microchip (formerly Supertex) integrated circuits (ICs), primarily because of my extensive experience with these. However, in this second edition, I introduce ICs from other suppliers and point out the similarities and differences between them. I have also updated the whole book and added new material, including descriptions of new ICs, new light-emitting diode (LED) driving techniques and chapters on both control systems and LED applications. A few minor errors in the first edition have now been corrected and I apologize in advance, in case I have introduced any new ones.

At the beginning of LED development, only those producing red light were available. But these were quickly followed by more colors: yellow/amber, green, and finally blue light, which triggered an explosion in applications. Applications included traffic lights, vehicle lights, and wall washes (mood lighting). LEDs that produce blue light have been combined with yellow phosphor to create white light, which is now one of the most popular colors for general lighting. The amount of light available from LEDs has also increased steadily, and now power levels, up to 20 W, are available using multiple LED die in a single package.

Driving LEDs require a constant current supply. Driving a single LED, or a long string of LEDs connected in series, has relatively few problems when the current is low (maybe 20 mA). High-current LEDs are tougher to drive, requiring 350 mA, 700 mA, 1 A, or a higher rating. Of course, a simple linear regulator could be used if power dissipation was not an issue, or a simple resistor, if current regulation is not critical.

However, in most applications, an efficient switching regulator is used. A switching regulator is essential if the load voltage is higher than the supply voltage (a series-connected LED string), where one needs to boost the voltage. A switching regulator is also needed if the supply voltage has a wide variation, and can be above or below the load voltage at any time, where a boost–buck regulator is needed. But switching means that electromagnetic interference, power dissipation, and parasitic elements have to be considered too. This book describes these in some detail with guidelines and solutions.

This book describes a number of LED driving methods. The main aims of this book are: (1) to show suitable types of LED driver topologies for given applications, (2) to work through some examples, and (3) how to avoid some of the mistakes that some engineers make when creating their own designs. However, the content is not exhaustive and further reading on some peripheral topics will be necessary to obtain a full understanding.

I dedicate this book to Scott Lynch, who died in July 2016 after a long and slow decline in health due to Parkinson’s disease. Outside work he was a keen surfer, mostly in Half Moon Bay, but had to give this up when his health declined. Scott was an excellent analog application engineer, being both meticulous and enthusiastic in his work. He was the expert on the switched linear regulator, CL8800, among other things. Scott was a great help to me during the 12 years that I worked with him in Supertex. Scott, may the surf be with you!

2017