For high brightness LED technology to succeed in replacing standard incandescent bulbs for high volume markets, the cost of the drive electronics required to power the LEDs must be kept to a minimum. This article, the fourth in a series discussing LED ballast design, presents a solution that exploits a novel constant power flyback converter architecture. This approach provides an ultra low cost 7W offline LED ballast that will run from 85–265Vac at 50/60Hz.