Power Supplies for LED Driving

Preface

The LED has been available for many years now, initially as a red colored indicator. Later, yellow/amber, green and finally blue colored LEDs became available, which triggered an explosion in applications. Applications included traffic lights, vehicle lights and wall-washes (mood lighting). Recently blue colored LEDs have been combined with yellow phosphor to create white light. The amount of light available from LEDs has also increased steadily, and now power levels of 1W, 3W and 5W are fairly common.

Driving a single LED, or a long string of LEDs connected in series, has relatively few problems when the current is low (may be 20 mA). High current LEDs are tougher to drive, requiring 350 mA, 700 mA, 1 A or higher. Of course, a simple ...