As a field applications engineer for one of the pioneering developers of integrated circuits for driving power LEDs, I meet many potential customers who have little or no idea of how to drive an LED properly. The older type of LED requiring a 20 mA supply can be abused to some extent. However, power requirements have been increasing; current ratings of 30 mA, 50 mA, 100 mA, 350 mA and higher are becoming common. There are several manufacturers that produce power levels up to 20 W, and more; these higher powers use LED chip arrays. If a power LED is abused, it tends to die very quickly.

Power LEDs are being used in increasing numbers; in channel lighting (signage), traffic lights, street lights, automotive, mood lighting (colour changing wall wash ), theatre lighting for steps and emergency exits. Names such as HB-LEDs (high bright) and UB-LEDs (ultra-bright) are becoming meaningless as the power levels continue to rise. This book will cover all types of LED drivers, from low power to UB-LEDs and beyond.

Is power LED driving simple? No, not usually. In a few cases a linear regulator can be used, which is simple, but most cases require a switching power supply with a constant current output. Linear driving is inefficient and generates far too much heat. With a switching supply, the main issues are EMI and efficiency, and of course cost. The problem is to produce a design that meets legal requirements and is efficient, with minimal cost.