A Compact Flicker-Free Transformer-Less LED Driver With an Enhanced Power Factor for Omnidirectional Multichannel Smart Bulb Applications

Abstract

In this paper, a flicker-free transformer-less multi-channel light-emitting diode (LED) driver that adopts a new power factor enhancement technique is presented. The proposed LED driver divides the transmission path of the current to the LED string in two ways depending on the instantaneous input voltage in order to improve the PF relative to that of a conventional compact flicker-free LED driver that uses a fixed LED current regulation scheme with only one electrolytic capacitor. The proposed driver can be implemented with a minimum number of external components leading to a compact module that allows a light bulb with omnidirectional light emission. In order to enhance the expandability of the smart bulb, a conventional buck converter with 3-V output is integrated with the proposed LED driver to supply the peripherals of the module. The proposed LED driver IC is implemented in a 0.35-mu m ultrahigh voltage CMOS process and occupies an area of 2.9 mm x 2.0 mm. A 10-W smart bulb prototype that adopts the proposed LED driver is flicker free and shows a power factor of 0.715 and power conversion efficiency of 77.5% for an ac supply of 120 V.