AC/DC converter free LED driver for lightings

This paper presents a noble AC/DC converter-free LED driver for LED lighting applications. The presented LED driver applies the AC mains power directly to the LED strings with no AC/DC converter stage, thus bulky transformer and life-time limiting electrolytic capacitor no longer needed. This small-sized, low-cost and reliable LED lighting driver was realized with an LED driver IC, which selectively empowers multi-channel LED strings based on the measured input AC voltage signal. The IC was fabricated in 1-um high voltage BCD process capable of handling AC input voltage up to 240 V. By PWM-controlling the LED-driving high-voltage switches, the IC resolved the thermal issue which is critical for the reliability of LED lighting module. A 4-W prototype LED driver module was implemented and tested to verify the feasibility of the suggested Converter-/Capacitor-less (ie. CC-less) LED driver scheme for low cost LED lighting.

I. INTRODUCTION

LED lighting is being considered as a promising illumination solution because of its superior efficiency, eco-friendliness, and longer life-time compared to the fluorescent and the incandescent lightings [1] [2] [3] [4] [5]. This LED lighting has been composed of two-stage (ie. a power factor corrector and a DC-DC converter) power converter scheme. However, in case of low-power products, the single-stage flyback PFC converter is more adoptable than two-stage scheme because of the efficiency and the complexity [6]. And this flyback converter scheme has the excellent output ripple performance, isolation, and line-/load-regulation performances. Nevertheless, it is very hard to make small-sized, long life-timed and low-cost LED lighting module with the flyback scheme, due to the transformer and the electrolytic capacitor.