Design of IC controller for dimmable compact fluorescent lamps with closed-loop control

Abstract

The use of Compact Fluorescent Lamps (CFLs) is growing rapidly worldwide not only because of its small size, but also because it saves more energy compared to the standard incandescent light bulb. In this thesis, an improved phase-controlled dimmable electronic ballast for CFLs is developed. The theory behind this dimmable ballast is based on the detection of dimming signal from the rectified main supply voltage. A phase angle is used as a dimming signal generated from a slightly modified conventional triac dimmer. Normally, this phase angle will appear in both rectified cycles, which have double the frequency of the mains. However, in this thesis, only alternating cycles are selected to extract the dimming signal as it can provide a more stable and consistent phase difference detecting mechanism. Moreover, a closed-loop control is implemented in this controller. This allows the intensity of the CFLs to change from 100% to 5% smoothly and linearly without noticeable fluctuation in brightness. The key concept of this closed-loop control is to monitor the fluorescent lamp current using a sensing resistor network. To reduce the complexity of the system and the size of the ballast, an IC controller is designed, simulated, fabricated and measured with good experimental results. Moreover, the whole dimmable CFL ballast can function properly without power factor correction circuit, which can significantly reduce the production cost and the size of CFL.

Date of Award	1999
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology