探究應用于LED背光的電光特性MFFL（無汞平面熒光燈）-韓國理工dissertation The Electro-Optic Characteristics of MFFL(Mercury-free Flat Fluorescent Lamp) for LCD Backlighting

Jukwang Lee, Jaechul Jung, Byungjoo Oh, Inwoo Seo, *Joongkyun Kim

and Ki-Woong Whang

School of Electrical Engineering, Seoul National University

San 56-1, Shinlim-dong, Kwanak-gu, Seoul 151-742, Korea.

* Department of Electrical Engineering, Hankyong National University

67, Seokjeong-dong, Anseong city, Gyeonggi-do, 456-749, Korea.

摘要 Abstract

在這項工作中，我們研究了多單元結構，高效的無汞平面型熒光燈（MFFL）的電光特性。In this work, we have studied the electro-optic characteristics of multi-cell structured, highly efficient Mercury-free Flat Fluorescent Lamp (MFFL).   http://ukthesis.org/Thesis_Writing/Accounting_Assignment/Engineering/   結果發現，每個新提出的單元格多小區結構MFFL可以操作獨立的脈沖幅度調制，和/或脈沖寬度和/或頻率調制，該方法可為有調光能力的LCD制造背光。 It was found that each cell of the newly suggested multi-cell structured MFFL could be operated independently by the pulse amplitude modulation, and/or pulse width and/or frequency modulation method which can be utilized to make a back light source for LCD with an areal dimming capability. A wide driving voltage margin of stable glow enabled to have a large luminance variation which resulted in the dimming ratio of 14%, while the frequency and the pulse width modulation resulted in the dimming ratio of 25 and 31% respectively.The interconnection of multi-cell structured MFFL for the full size LCD together with its driving wave form for the independent operation of each cell with a 4 bit sub-field method and its consequent 16 level lighting for each TV field are suggested.

介紹 1. Introduction

As the TV application of LCD is actively pursued, a new back lighting system (BLS) is asked for because of the demerits of current BLS using Cold Cathode Fluorescent Lamps (CCFL) such as the high power consumption and usage of Mercury. 一個智能是有面調光能力的背光系統，可以降低電力消耗，并增加了灰色縮放表達能力。An intelligent back lighting system with areal dimming capability was suggested to reduce the power consumption and increase the gray scale expression capability. [1] The BLS using Light Emitting Diode (LED) shows excellent lighting characteristics and is expected to be a good candidate for the next generation BLS if the cost can be brought down. [2] It has been suggested that a new type of Mercury-free flat light source can be realized with a high luminous efficiency.#p#分頁標題#e#

In this work, its dimming capability has been studied. It has been suggested that an independent control of the lighting level of each cell in the multi-cell structured MFFL

for the full sized 32” or larger LCD can be realized using a subfield method. The interconnection of the cells and the driving wave form for the areal 16 level, 4 bit lighting are suggested.

2. Experimental Setup

The unit cell has the same structure as reported before [3] and shown in figure.1. The parallel-running, main electrodes are separated by 70mm and covered by 80 ? dielectric material.

The auxiliary electrode is located on the opposite plate and used as the data electrode. The barrier rib height is 3mm. A mixture of Ne-Xe was used as the discharge gas. The Xe concentration was varied between 4~18% and pressure 60~150 Torr.Figure 1. Structure of the multi-cell MFFL

3. Results

MFFL基本特性 3.1 Basic characteristics of MFFL The dimming characteristics of a unit cell have been studied and their results are shown in figure.2. The discharge cell has Ne-Xe

(18%) mixture with the pressure of 100 Torr. When the main pulse amplitude is changed from 2.5 kV to 1.9 kV at the pulse frequency of 13.3 kHz, the luminance changed from 8150 cd/m2 to 1120 cd/m2, thus resulting a dimming ratio of 14% and the consumed power from 4 W to 0.4 W. When the frequency is changed from 16 kHz to 20 kHz, the luminance increased from 2180 cd/m2 to 8700 cd/m2, thus resulting a dimming ratio of 25% while the increase of pulse width from 1.5 μsec to 2.4 μsec resulted in the increase of luminance from 2450 cd/m2 to 7960 cd/m2 and a dimming ratio of 31%.

Figure 2.1 Voltage dimming & Power

85 mm

85 mm

ISSN0006-0966X/06/3 1422 • SID 06 DIGEST 702-1422-$1.00+.00 © 2006 SID

38.2 / J. Lee

Figure 2.2 Frequency dimming & Power

Figure 2.3 Duty ratio dimming & Power

Figure 2. Dimming Characteristics by Various methods The MFFL generates the plasma using a dielectric barrier discharge (DBD) to generate VUV (Vacuum Ultra Violet) ray.

Figure.3 represents the time evolution of the driving voltage,current, IR (823&828nm) and blue visible light, which shows very fast response time. The total delay time of discharge consists of the formative and the statistical delay after the application of voltage pulse.

Figure 3. Time Evolution of Voltage, Current, IR and Visible light emission

Figure.4 shows the dependency of the discharge delay time in various panel temperatures. As the panel temperature decreased from 40 °C to -15 °C, the formative delay time increase from 195 ns to 265 ns while the statistical delay time from 10 ns to 30 ns. The total discharge delay time is about 200 ns at 40°C and 300ns at -15°C, both of which are still quite small values when compared to the liquid crystal’s response time. Fast response time of MFFL backlight suggests to use the pulse number modulation

scheme with a sub-field dimming control method to give a digitized control of light level of the designated TV field.

Figure 4. Discharge delay time vs various temperature

調光控制面板 3.2 Areal dimming control

MFFL用作簡單比較長間隙放電一對主電極，而在放電點火引起的之間輔助電極和其中一個的局部放電主電極。The MFFL uses relatively long gap discharge between the simple pair of main electrodes while ignition of the discharge induced by the local discharge between the auxiliary electrode and one of main electrode. The operation voltage margin can be changed by those auxiliary voltage signals. Figure.5 shows the operation margin changes as the auxiliary voltage signals vary. We can turn on cells among multi-cell structured MFFL selectively by changing the auxiliary voltage signal level from V0 to V3 while the sustain voltage signal level of main electrodes are the same.

The marked area represents the dynamic driving margin of one cell and common dynamic driving margin exists so we can operate selective turning on operation.

Figure 5. Dynamic driving margin of MFFL

Figure.6 shows the interconnection for 3