Comparison of different driving methods for LED general lightings

Pao Yue-kong Library Electronic Theses Database

Comparison of different driving methods for LED general lightings

 

Author: Cui, Ning
Title: Comparison of different driving methods for LED general lightings
Degree: M.Sc.
Year: 2012
Subject: Light emitting diodes -- Power supply.
Electric power supplies to apparatus.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Electronic and Information Engineering
Pages: 102 leaves : ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2531562
URI: http://theses.lib.polyu.edu.hk/handle/200/6763
Abstract: Light emitting diodes (LEDs) are likely to be used for general lighting applications due to their high efficiency and longer life. While LED devices enjoy relatively long lifetime, the relatively short lifetime of LED drivers, which is limited by the use of electrolytic capacitors, remains a limiting factor to the lifetime of the overall LED lighting system. When the LED drivers utilize the commercial ac voltage source, the function of power factor correction (PFC) should be realized to achieve a high power factor, due to the increasing concern in environmental protection and demand of maintaining of the power quality of ac power lines. These two points, namely, long lifetime and high power factor, are imperatives to be addressed. The purpose of this thesis is to implement and compare different driving methods for LED general lighting with long lifetime. Two classifications electrolytic capacitor-less power-factor-corrected driving methods are introduced and implemented. Simple yet effective peak-to-average ratio reduced method and modeling solution of open-loop bi-directional boost/buck converter are proposed and implemented. In this thesis, the method of using pulsating current to drive LEDs is introduced and implemented firstly; and then a relatively practical method to reduce the peak-to-average ratio and improve the dynamic response performance is proposed. The corresponding simulation and experiment results to verify the effectiveness are presented. Even though, this method suffers the problem of flickering at twice the line frequency and large overshoot. So the third part of this thesis is dedicated to reduce the peak-to-average ratio, or even eliminate the flickers. The concept "flicker-free" is introduced and corresponding driving circuits are implemented. A method based on state-space averaging and passive filter principles to analyze an open-loop boost/buck bi-directional converter is proposed. This method of analysis is proven by simulation and experiment consequently. Finally, in order to achieve the goal of eliminating the electrolytic capacitor and flickers simultaneously, an active filter based on bi-directional boost/buck converter is implemented. Compared with the other circuits, the active filter can also achieve high power factor, to be electrolytic capacitor-less and flicker-free.

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