On supplying LEDs from very low dc voltages with high frequency AC-LED drivers

Abstract

This work studies the driving of white Light Emitting Diodes (LEDs) from very low voltages in the range of 1.2 to 2 V. The proposed idea is based on replacing the standard Schottky diode used in conventional converter topologies (i.e., buck, buck-boost and boost) with an LED, while shortcutting the output of the converter. In this configuration, the LED works both as the load and as the rectifier diode of the converter, hence, switching the LED at high frequencies (i.e. > 100 kHz). Moreover, a thorough analytical study is carried out for the two topologies rendered in this work. Particularly emphasizing their static analysis and the obtaining of the boundaries between the different conduction modes. Finally, the idea is validated experimentally by means of the boost converter variation (i.e., DL//S AC-LED driver). The DL//S AC-LED driver has also been compared with a dc-dc boost converter showing a better luminous efficacy while disposing of the Schottky diode and the output capacitor. This analysis is carried out when connected to a Li-Ion battery using a simple control and integrated circuit for its development