LED drivers for combined illumination and visible light communications

Abstract

Solid State Lighting (SSL) with High-Brightness LEDs (HB-LEDs) results in energy savings due to high efficacy of HB-LEDs. Energy savings has led to the replacement of traditional lighting systems such as incandescent, fluorescent and metal halide lamps by LED lighting. Unlike traditional lighting sources, the unique properties of LEDs include generation of multiple colors and the ability to modulate at high-speed. Due to these properties, LED lighting will create emerging applications in healthcare, education, agriculture and communications.

In the first part of this work, AC-DC power converters providing both illumination control and VLC are presented. The proposed dual-purpose LED drivers provide constant current output with flicker free dimming while modulating LEDs for VLC. Pulse shaping of the current flowing through LEDs will improve their bandwidth. The proposed converter has resulted in inherent pulse shaping and hence improved the bandwidth of LEDs. In the second part of this work, power converters for multi-color LED lighting systems are developed. In these systems, LED drivers should provide independently controllable constant currents to each LED string for achieving tunable lighting spectrum. We have proposed a simple, modular and scalable control scheme for driving multi-color LED strings. The proposed driving technique is used to develop multi-color LED drivers with both DC and AC inputs. For multi-color LED drivers with DC input, a single inductor is used to provide multiple independently controllable constant current outputs. Hence these class of power converters are called as Single Inductor Multiple Current Output (SIMCO) converters. Finally, a single stage multi-color LED driver using the proposed control scheme for AC input is proposed. This converter also provides high-power factor to the AC mains. SIMCO converter and single stage–multi color LED drivers are experimentally validated. Detailed small-signal modeling for control implementation and design considerations of dual-purpose LED drivers and multi-color LED drivers are presented in this thesis.

LEDs modulated at high-speeds can transmit data in free space providing both Visible Light Communications (VLC) and illumination. This dual use of LED lighting is also called as Light-Fidelity (Li-Fi) technology, which is similar to the RF based Wireless Fidelity (Wi-Fi) technology. However, LEDs have non-linear electrical load characteristics. In addition, LEDs in lighting systems have to be interfaced with the available power sources (AC or DC). Power converters (LED Drivers) process the power from input sources and matches them to LED load characteristics.