Thesis Examination Committee
Prof Wing Hung KI, ECE/HKUST (Chairperson)
Prof Philip MOK, ECE/HKUST (Thesis Supervisor)
Prof Chi Ying TSUI, ECE/HKUST
Light-emitting diode (LED), an optoelectronic device to emit energy in the form of light, is a revolutionized invention of the 21st century to substitute the conventional light sources due to the long lifespan and high efficacy advantages. However, the traditional converter-based LED drivers require many large off-chip components which are expensive and space-consuming. Moreover, the high AC voltage application (220 – 240 VAC) and the reduction of harmful low-frequency optical flicker are also the most challenging problems in AC LED driver design. The aim of this thesis is to reduce the low-frequency flicker, maintain the good driving performance and achieve system miniaturization with small passive components.
A direct AC LED driver with low-frequency flicker reduction is presented. A charge-based 1/x circuit is implemented to stabilize the LED output power and provide dimming compensation feature. The designed driver, including controller and power transistors, was fabricated in GlobalFoundries 0.18-µm 700-V ultra-high-voltage (UHV) process. The LED driver delivers a maximum 20-W power to the LEDs with only a 47-µH inductor and two 10-µF capacitors at input voltage range of 220 – 240 VAC, 50-Hz. This work achieves 94% peak efficiency and power factor of 0.91. Besides that, the harmful low-frequency flicker is mitigated over 70% with the help of the hysteretic average current-mode control scheme.