On Supplying LEDs from Very Low dc Voltages with High Frequency AC-LED Drivers

Abstract

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