Examination Committee

Prof Jin WANG, SOSC/HKUST (Chairperson)
Prof Philip MOK, ECE/HKUST (Thesis Supervisor)
Prof Po-Hung CHEN, Electronics Engineering Department, National Chiao Tung University (External Examiner)
Prof Wing Hung KI, ECE/HKUST
Prof Chi Ying TSUI, ECE/HKUST
Prof Huamin QU, CSE/HKUST
 

Abstract

Light-emitting diodes (LEDs), as an emerging lighting source with several supreme benefits, are edging out their conventional counterparts throughout the world. In order to take advantages of these benefits, the driver circuits with high power conversion efficiency, sufficient lifetime, and minimized system size and cost are required. Among a variety of AC input LED drivers, the inductor-less linear driver emerges as a promising solution because it not only shows great potential to achieve system miniaturization but also is free from the substantial switching losses. However, there are remaining issues for the existing inductor-less drivers, such as the harmful optical flicker and the poor energy utilization for powering the low voltage controller IC. 
 
The first part of this research, including two developed inductor-less LED driver prototypes, is to overcome the above issues for efficient lighting. In the first design, a quasi-constant power control scheme is proposed to mitigate over 80% of the flicker at the double-line frequency while the 87.3% efficiency and an over 0.9 power factor are maintained. In the second design, a multi-source power supply scheme is proposed to power the controller IC with the jointed nodes on the LED string, which are naturally provided by the inductor-less driver, so the energy can be delivered to the controller efficiently without introducing extra expensive and bulky components. The measured results show that the 2.1% and 3.8% efficiency improvement are achieved for low flicker mode and high power factor mode, respectively, at around 5-W output power.
 
In the second part, the lighting technology beyond general illumination is also investigated. An inductor-less driver prototype is developed with the integration of a visible-light-communication technique for simultaneously providing illumination and data transmission. The proposed driver has less stages and does not have passive components speed limitation. Besides this, the flicker is further mitigated to below 10% with an accurate 1/x circuit and the dimming compensation. With the help of keep-and-restore technique and auxiliary turn-on switch, the driver supports up to 8-Mpbs on-off-keying non-return-to-zero data transmission.