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

This paper presents an ac-dc LED driver that consists of two-parallel inverted buck converters. To buffer the twice-line-frequency energy, one inverted buck converter (also known as a floating buck converter) conveys energy to a storage capacitor, simultaneously performing the power factor correction. The other inverted 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 design procedure to achieve a high power factor, while minimizing the storage capacitance 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 experimentally. 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.