Description: Learn "how to" design an isolated constant current source to drive high power LED's from an AC power line. The constant current source is built using a flyback topology and has an efficiency greater than 80%. Conventional current sources need many components for this. This application is a low-cost solution based on an innovative circuit (patent filed) using a Fairchild Power Switch (FPS). The converter is a primary side regulated removing the need for an optocoupler and other additional components.