Offline LED Driver for ENERGYSTAR® Residential LED Luminaire Applications - GreenPoint® Reference Design

This reference document describes a built-and-tested, GreenPoint solution for an isolated 8 W constant current LED driver which is intended to support the residential power factor requirements of the DoE ENERGY STAR Standard for Solid State Lighting Luminaires (Version 1.1 − 12/19/08). Some of the typical products in this category include portable desk lamps, under-cabinet lights, and outdoor porch lights.

One of the most common power supply topologies for low power offline LED drivers is an isolated flyback topology. Unfortunately standard design techniques used for these supplies typically result in a power factor in the range of 0.5−0.6. This design note describes why the power factor is low and discusses techniques to improve the power factor. Finally it illustrates how an existing design was modified to substantially improve the power factor and easily comply with the residential power factor requirements.