An AC-DC LED Driver with a Two Parallel Floating Buck Topology for Reducing the Light Flicker in Lighting Applications to Low-Risk Levels

Abstract

This dissertation presents an ac-dc LED driver that consists of two parallel floating buck converters. To buffer the twice-line-frequency energy, one floating buck converter conveys energy to a storage capacitor, simultaneously performing the power factor correction (PFC). The other floating buck converter regulates the LED current to maintain a constant brightness in the LEDs for reducing the light flicker to low-risk levels. The proposed architecture reduces the voltage stress and the size of the storage capacitor, enabling the use of a film capacitor instead of an electrolytic capacitor. Considering the power factor and the flicker standards, a de-sign procedure to achieve a high power factor, while minimizing the storage capac-itance and the LED current ripple, is presented. A prototype of the proposed LED driver has been implemented with an on-chip controller IC fabricated in a 0.35 μm CMOS process and its functionality and performance have been verified experi-mentally. It demonstrates a power factor of 0.94 and a peak power efficiency of 85.4% with an LED current ripple of 6.5%, while delivering 15 W to the LEDs.