A Novel Of ZVS Using Phase Shift Driving For CCFL

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1 Novel Of ZVS Using Phase Shift Driving For CCFL Te-Lung Shih Jyh-Wei Chen Department of Electrical Engineering Tatung University, Taipei, Taiwan bstract This paper is a novel of ZVS using phase shift driving for CCFL. That has introduced power converter that designs with power saving, lightweight, higher efficiency dimmable, and ZVS. This is application in power converter of LCD TV/Monitor. This power converter divides into two stages. One is C/DC power converter the other is backlight inverter. The flyback converter is structure of C/DC power converter. Output voltage of this converter is 5 V and 12 V. 12 V is dc link voltage of backlight inverter. The output voltage of backlight inverter is 1800 V in transient. Due to negative load characteristic output voltage is down to 600 V in steady state. This circuit already drivers for four branch CCFL and is dimmable by feedback control. Keywords: C Power converter, acklight inverter, Dimmable, ZVS. /. / 5 V 12 V 12 V 1800 V 600 V (Cold Cathode Fluorescent Lamp, CCFL) I. Introduction Since Liquid Crystal Display (LCD) is introduced to the world, having the advantage of lightweight, small size, no radiation, low power consumption, low temperature, long life and soft picture, it gradually replaces traditional CRT Display. The most important part in LCD is Cold Cathode Fluorescent Lamp (CCFL). Fluorescent major attributions is negative resistance. The negative resistance is shown in Fig.1. It is a low pressure mercury discharge lamp. The structure inside the tube is having a layer of Fluorescent, which is sealed with little quantity of non active gas and mercury.[1] When this mercury atom is discharging, with impacts with electrons, it produces UV ray, after which passing fluorescent, it becomes visible light. When adding voltage from two ends of tube, it starts to discharge, the mercury electrons and gas atom will impact with each other and produces UV ray. The UV ray meets the fluorescent at the tube surface, it transfers to visible light. Due to CCFL do not use filament, there is no issue of limited filament life span; therefore, CCFL has very reliable life time. Fig. 1 The negative resistance characteristic II. The Proposed Circuit Structure The proposed system function diagram for CCFL is shown in Fig. 2. Fig. 2 The proposed system function diagram (1) C\DC Power Converter The proposed C\DC power converter is shown in Fig. 3. The flyback converter is DC\DC power converter. Input voltage is dc 155 V and two of output voltage. One is 5 V, another is 12 V. 5 V supply IC source in board and 12 V that is input voltage in inverter. Fig. 3 Flyback converter (2) acklight Inverter [2]-[6] The proposed backlight inverter is shown in Fig. 4.

2 Fig. 4 The proposed backlight inverter The gating signals and key waveforms of the proposed circuit are shown in Fig. 5, and the circuit operations of each mode shown in Fig 6 are explain as follows: Mode 1: [t1] Through Vin to conducted, at same time, charged at this moment. Mode 2: [t2] Q Vin, Q2 and Q3 voltage are V ( I )is increased. C2 is also 2 off and anti-electromotive force to made discharge I Direction has changed from V Through Q3 and conducting body diode D4 of Q to V. On this mode no voltage from V doing 4 switching called ZVS. [7] Mode 3: [t3] Conducting V andv to Vin byq 3 and Mode 4: [t4] Turn offq3 will conduct D1 and will charge positive current to C 1. Mode 5: [t5] Turn on Q 1 to drive voltage and current into transformer. Mode 6:[t6] Turn-off Q3 and turn-on Q 2, due to transformer anti-electronic force, it conducts D 3, and C1 discharge. Mode 7 [t7] Turn-onQ 1 and keepq 2 on to drive V = V prepare for another phase. Mode 8:[t8] Start another cycle from Mode1. in Fig.5 The gating signals and key waveforms of the proposed circuit Mode 1 Mode 2 Mode 3

3 Mode 4 Fig. 7(a) Mode 5 Mode 6 Fig. 7(b) Mode 7 III. Experiment Result Following is experimental waveforms. Fig.8 illustrates gate driver signals experimental waveforms. Fig.9 illustratesv andv in phase waveform. Fig.10 illustrates V andv out phase waveform. Fig.11 illustrates voltage and current waveform of the lamp. Fig.12 illustrates start up voltage and current waveform of the lamp. Fig.13 illustrates voltage and current of 10% bright waveform of the lamp. Fig.14 illustrates voltage and current of 50% bright waveform of the lamp. Fig.15 illustrates voltage and current of 100% bright waveform of the lamp. [8] Fig.16 Harmonic analysis of output voltage.[9][10] Mode 8 Fig. 6 The blight inverter of each mode operation (4) Phase Shift Technique Fig. 7(a)(b) shows the definition of phase shift for two different situations. y increasing the phase shift between the two half-bridges, the amplitude of the first harmonic of the resulting full-bridge voltage increases. So, phase shift control corresponds to amplitude control.

4 Fig. 8 Full-bridge gate signals Fig. 12 Lamp of voltage and current Fig. 9 Fig. 13 Lamp of voltage and current (10% right) Fig. 10 V andv out phase waveform. Fig. 14 Lamp of voltage and current (50% right) Fig. 11 Start up Lamp of voltage and current Fig. 15 Lamp of voltage and current (100% right)

5 Fig. 16 Harmonic analysis of output voltage IV. Conclusion novel of ZVS using phase shift driving circuit for the CCFL has been presented. It features a dimming control with high efficiency, adjustable sensitivity, even brightness in multi-lamp system, a more stable closed loop, less lamp flickering problem, and a simple circuit. The ZVS in Full-bridge driving circuit, a working procedure for the driver was presented. n experimental circuit was built based on outcome of the working procedure. The measured results agree well with analytical results. The above circuit has improved operation efficiency, reduced switching loss and EMI. The Phase Shift stablizes the control of lamp current amplitude, linearizes brightness control for the CCFL lamps. Reference [1] [2] 2003 [3] [4] [5] W. Pabst and D. Klien, Igniting high-pressure lamps with electronic ballast, Journal of the illuminating Engineering Society., pp [6] M. Ponce,. Lopez, J.Correa, J.rau, and J. M. lonso, Electronic ballast for HID lamps with high frequency square waveform to avoid acoustic resonances, pplied Power Electronics Conference and Exposition, PEC Sixteenth nnual IEEE., Vol. 2, pp , [7]. F. de Souza and I. arbi, New ZVS Semiresonant High Power Factor Rectifier with Reduced onduction Losses, IEEE Transactions on Industrial Electronics., Vol. 46, No. 1, pp , Fed1999. [8] [9] R. P. Verderber, O. C. Morse, and W. R. lling, Harmonics from Compact Fluorescent Lamps, IEEE Industrial pplications Society nnual Meeting., pp , [10] R. Christiansen, Effect of High Levels of Harmonics from Lighting Equipment and System, IEEE Industrial pplications Society nnual Meeting., pp , 1991.

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