英语论文网

Abstract
This paper presents a low-frequency square-wave drive,consisting of a single high voltage converter, an ac lamp ignitioncircuit, current control devices代写留学生论文 and a single backlight controller,capable of driving an arbitrary number of parallel cold cathodefluorescent lamps (CCFLs) with independent accurate lampcurrent regulation. Key to the architecture is a proposedcapacitive coupling approach for ac lamp ignition that results inreliable, simultaneous ignition of parallel lamps with a maximumignition voltage near the normal lamp operating voltage. A briefsummary of the lamp model and behavior is presented to explainthe findings during the capacitive ignition and low-frequencyoperation. Experimental results are presented demonstratingparallel lamp ignition and current regulation for four, 250 mmCCFLs

1. Introduction
Large screen LCD TV backlighting systems, generally consistingof 16 or more cold cathode fluorescent lamps (CCFLs), require aballast capable of driving all or groups of lamps in parallel withaccurate current control and regulation. The most commonelectronic ballasts, based on high frequency LCC resonantinverters, are capable of driving at most four lamps in parallel andrequire complex multi-winding transformers and specializedcontrol circuitry. This solution suffers from several disadvantages,the major limitation being the inability to simultaneously maintainhigh efficiency, proper lamp ignition, and individual lamp currentregulation.

We present a suitable architecture, capable of driving a largeparallel CCFL array with high efficiency, accurate lamp currentcontrol and near operating voltage lamp ignition. The systemblock diagram, shown in Fig. 1, is based on low-frequencysquare-wave (LFSW) drive and removes many of the drawbacksassociated with a high frequency drive, including energy lossthrough capacitive coupling, the thermometer effect luminanceuniformity degradation and electromagnetic interference (EMI).The proposed architecture is capable of driving a large parallelCCFL array with only a single high voltage and high efficiencyconverter, resulting in reduced size, weight and cost over existingdesigns. Reduced ignition voltage (at near operating voltage) isachieved by a unique capacitive coupling approach, based on thesimilar principles to normal operation of electrodeless or externalelectrode fluorescent lamps. However, the displacement current isonly required in our proposed architecture as a short highfrequency pulse during cold lamp ignition, which triggerssimultaneous lamp ignition of all parallel lamps. High impedancecurrent source circuit (based on MOSFET current mirror) isconnected in series with each lamp to ensure individual lamp current regulation and control. In this paper, we discuss a suitable architecture for large CCFL arrays and study new approaches for lamp ignition to enable low frequency drive.

7. References
[1] M. Doshi, R. Zane, F. Azcondo, “Low FrequencyArchitecture for Multi-Lamp CCFL Systems with CapacitiveIgnition,” Applied Power Electronics Conference (APEC),6 - 10 March 2005, Austin, Texas, pp. 1072–1078.
[2] J. Williams, “Fourth Generation of LCD BacklightingTechnology,” Linear Technologies Corporation, ApplicationNoteAN-65,Oct.1995.
[3] John W A M Gielen, et. al., “Axial mercury segregation indirect current operated low-pressure argon-mercury gasdischarges: P本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。