T.-S. Cho et al.: A Low-Temperature Driving Scheme of EEFLs Inverter for LCD TV Backlights

Contributed Paper Manuscript received January 13, 2009 0098 3063/09/$20.00 © 2009 IEEE

699

A Low-Temperature Driving Scheme of EEFLs Inverter for LCD TV Backlights

Tae-Seung Cho, Member, IEEE, Jin-Woo Jung, Member, IEEE, Dong-Myung Lee, Member, IEEE, Eun Ha Choi, Member, IEEE, and Guangsup Cho

Abstract — A new low-temperature driving method of

EEFLs (External Electrode Fluorescent Lamps) inverter for LCD TV backlights is proposed. The proposed driving scheme achieves a zero current switching (ZCS) of lower switches and dramatically reduces the temperature of the transformer at which the power loss mainly occurs. Moreover, the capacitance of EEFLs is calculated by the Q-V Lissajous analysis method and then the optimal switching interval for a low heating loss of the transformer is determined. To investigate the feasibility of the proposed driving method, various experimental results using a prototype 17-inch LCD TV backlight with 12 EEFLs are presented1.

Index Terms — Driving circuit, driving method, EEFL, full-bridge inverter, LCD backlight, low temperature, trapezoidal waveform.

I. INTRODUCTION In recent years, large-screen flat panel display (FPD)

market is dramatically growing due to digital TV broadcasting and consumers’ needs. Among FPDs, Thin Film Transistor-Liquid Crystal Display (TFT-LCD) has been one of the most attractive devices because of some benefits such as high brightness, light weight, high resolution, thinness, low power consumption, and high contrast ratio, etc. However, the TFT-LCD inevitably needs the Back Light Unit (BLU) because it is not an emissive display device. Fig. 1 (a) and (b) shows the structures of a Cold Cathode Fluorescent Lamp (CCFL) and an External Electrode Fluorescent Lamp (EEFL). In past years, the CCFL shown in Fig. 1 (a) has been mainly used as a backlight source for LCD light emission [1]-[3]. However, it has some drawbacks in the following. First, the CCFL has a short lifetime because of the oxidation of the internal electrode which gas particles collide with. Next, it requires a ballast

1This work was supported by the Dongguk University Research Fund of

2008. Tae-Seung Cho is with the PDP Development Team, PDP Division,

Samsung SDI Co., Ltd., Cheonan, 330-300, Korea. Jin-Woo Jung is with the Department of Electrical Engineering, Dongguk

University, Seoul, 100-715, Korea (e-mail: jinwjung@dongguk.edu). Dr. J. W. Jung is a corresponding author.

Dong-Myung Lee is with the School of Electronics and Electrical Engineering, Hongik University, Seoul, 121-791, Korea.

Eun Ha Choi is with the Department of Electrophysics, Kwangwoon University, Seoul, 139-701, Korea.

Guangsup Cho is with the Department of Electrophysics, Kwangwoon University, Seoul, 139-701, Korea.

capacitor due to negative resistive characteristics. Furthermore, it has an unbalancing current when one inverter drives many lamps in parallel. Accordingly, if the size of the LCD panel is a 32-inch, it needs about 16 ~ 20 CCFLs and corresponding inverters and ballast capacitors. To solve these problems above, the EEFL has been proposed as a new backlight source [4]-[12]. As shown in Fig. 1 (b), the EEFL has not an internal electrode but an external electrode. As a result, it has a longer lifetime, higher efficiency and higher luminance compared with the CCFL. In addition, multiple EEFLs can be driven in parallel by only one inverter since each EEFL has a small capacitance and they operate like a ballast capacitor. Consequently, it leads to the uniform brightness of the lamps, compact size, low cost and light weight of the inverter. Therefore, the EEFL is one of the most promising backlight sources that can replace conventional CCFL mainly used for LCD BLU.

(a)

(b)

Fig. 1. Structures of CCFL and EEFL. (a) CCFL. (b) EEFL.

As depicted in Fig. 1 (a), the plasma discharge in CCFL directly occurs through the internal electrodes and the sinusoidal voltage is applied to both end electrodes by the LC-resonant inverter [1]-[3]. Meanwhile, the EEFL can be driven by both square [7]-[8] and sinusoidal [8]-[12] voltage waveforms because the discharge currents flow by the movement of the wall charges in the glass tube. In general, the

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square wave inverter does not need the transformer, whereas the sinusoidal wave inverter includes the transformer to utilize the resonance between the leakage inductance of the transformer and the capacitance of the EEFLs.

In this paper, a new low-temperature driving scheme of EEFLs inverter for LCD TV backlights is proposed and its circuit operation is addressed in detail. The proposed driving method is implemented by a series-resonant full-bridge inverter with a transformer and the trapezoidal voltage waveform is applied to both external electrodes of EEFLs. It achieves a zero current switching (ZCS) condition of lower switches. Furthermore, the capacitance of EEFLs is calculated by the Q-V Lissajous analysis method and then the optimal switching interval for a low temperature of the transformer is determined. Consequently, the proposed technique dramatically reduces the temperature of the transformer which consumes most power loss. To demonstrate the effectiveness of the proposed driving scheme, various experimental results using a prototype 17-inch LCD backlight unit with 12 EEFLs are presented.

II. DRIVING CIRCUITS AND OPERATIONAL PRINCIPLES

A. Conventional Driving Circuits and Driving Methods Fig. 2 shows a schematic diagram of EEFL backlight driven

by a square wave or a sinusoidal wave inverter and as shown in this figure only one inverter supplies square wave or sinusoidal wave pulses to a number of EEFLs connected in parallel [7]-[12]. Generally, one of a push-pull, a half-bridge or a full-bridge inverter can be adopted to drive multiple EEFLs according to applications.

Fig. 2. Schematic diagram of EEFL backlight driven by one inverter.

The conventional square wave driving circuit and equivalent circuit model are depicted in Fig. 3. Fig. 3 (a) shows a square wave full-bridge inverter and in general, there is no transformer in this driving circuit and then it is expected that the power efficiency is improved. However, the cascade multi-stage inverter should be used to apply much higher voltage than a DC-link (VDC) to both ends of EEFLs and it makes the system cost high [7]. Fig. 3 (b) shows an equivalent circuit model with a resistor (REEFL) and a capacitor (CEEFL) for EEFLs.

(a)

(b)

Fig. 3. Conventional square wave driving circuit and equivalent circuit model. (a) Square wave full-bridge inverter without a transformer. (b) Equivalent circuit.

Fig. 4 shows the driving methods of the square wave inverter [7]-[8]. As shown in Fig. 4, the lamp current (IO) has the pulse shape when the square wave is applied to both external electrodes of the lamps because there is no inductive element that generates the resonance with the capacitance of the EEFLs. Additionally, the wall charges in the glass tube have two discharge modes in this circuit: main discharge and self discharge. The self discharge occurs when the wall voltage induced by the wall charges accumulated in the previous pulse exceeds the breakdown voltage. In this figure, the self discharge is observed when VO holds zero voltage, and it is a typical phenomenon in the dielectric barrier discharge of alternating current plasma display panels [13]-[17]. Otherwise, there exists only main discharge mode.

(a) (b)

Fig. 4. Conventional square wave driving methods.(a) Without self-discharge. (b) With self-discharge.

As shown in Fig. 4 (a), when a square pulse voltage (VO) is

high enough to discharge and goes from VDC to −VDC or vice versa, the main discharge occurs. It is because the dielectric barrier of the glass tube restricts the discharge current and the wall charges are accumulated on both sides of the dielectric

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T.-S. Cho et al.: A Low-Temperature Driving Scheme of EEFLs Inverter for LCD TV Backlights 701

surface around the electrode. And the induced wall voltage between the wall charges of different polarities balances the applied voltage during the sustaining pulse period. Meanwhile, there exist both main discharge and self discharge in Fig. 4 (b). The main discharge occurs when the voltage (VO) applied to the EEFLs goes from 0V to VDC or −VDC, while the self discharge happens by the electric field due to the reversed wall voltage caused by the wall charges when the voltage (VDC or −VDC) falls to the ground level.

Fig. 5 shows the conventional sinusoidal wave driving circuit with a transformer and equivalent circuit model [8]-[12]. In Fig. 5 (a), the sine wave full-bridge inverter has a transformer and then the high voltage can be easily applied to the lamps by regulating the transformer’s turn ratio. As shown in Fig. 5 (b), the EEFLs can be modeled by a resistor (REEFL) and a capacitor (CEEFL), and denoting the transformer’s turn ratio as 1:n, the secondary impedances (REEFL and CEEFL) can be transferred in the primary terms (REQ and CEQ). Therefore, the soft switching scheme (ZVS or ZCS) can be realized because this topology provides the resonance between the leakage inductance (Lleak) and the capacitance (CEQ) of the EEFLs.

(a)

(b)

Fig. 5. Conventional sinusoidal wave driving circuit and equivalent circuit model. (a) Sinusoidal wave full-bridge inverter with a transformer. (b) Equivalent circuit.

Fig. 6 shows the conventional sinusoidal driving method. This scheme can reduce the voltage stress of power switches (X_H, X_L, Y_H, Y_L). It is the reason why the power switches are placed on the primary side of the transformer and the DC-link voltage (VDC), which determines their voltage ratings, is relatively low. That is, a low primary transformer voltage (VXY) can be readily boosted by adjusting the turn ratio. Moreover, it achieves the soft switching techniques of the switches, and then this method makes the system cost low and the power efficiency high. However, an additional power loss

occurs at the transformer compared with the square wave driving method. As shown in Fig. 6 (a) and (b), there are two operation modes: below resonant frequency mode and above resonant frequency mode. In both cases, the primary transformer voltage (VXY) has a square wave form with some zero voltage intervals, while the secondary voltage (VO) of the transformer has a sinusoidal wave form. Below resonant frequency mode means that the switching frequency is lower than the resonant frequency. In this mode, the fundamental-frequency component (V1) of the primary transformer voltage (VXY) lags the primary current (IXY) of the transformer and a ZCS technique is possible. Next, above resonant frequency mode denotes the switching frequency is higher than the resonant frequency. In the mode, the fundamental-frequency component (V1) of VXY leads the primary transformer current (IXY) and a ZVS scheme is applicable. In case MOSFETs are used as the switching devices, above resonance mode may be better than below resonance mode from the point of view of power efficiency.

(a) (b)

Fig. 6. Conventional sinusoidal wave driving methods. (a) Below resonant frequency. (b) Above resonant frequency.

B. Proposed Driving Method and Circuit Operation Fig. 7 (a) shows a schematic diagram of EEFL backlight for

a 17-inch LCD TV used in this paper. As shown in Fig. 7 (a), 12 EEFLs are placed in parallel between a diffusion plate and a reflection sheet, and lamp connectors with external electrodes are put at both ends. Fig. 7 (b) illustrates the full-bridge inverter with a transformer. Fig. 7 (c) shows the equivalent circuit model of the EEFL inverter in Fig. 7 (b). Fig. 7 (d) shows the proposed driving method and key waveforms to significantly reduce the power loss of the transformer. In Fig. 7 (d), the primary and secondary voltages of the transformer have trapezoidal waveforms although the series-resonant full-bridge inverter includes a transformer. As shown in Fig. 7 (d), the proposed driving scheme is different from those of Figs. 4 and 6.

Based on Fig. 7 (d), Fig. 8 shows the operational mode diagrams during one period (t0 ~ t8), and the dotted lines on the primary side denote the current paths. As depicted in Figs. 7 (d) and 8, the circuit operation is divided into eight modes for one period, and the detailed analysis is as follows.

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(a)

(b)

(c)

(d) Fig. 7. Proposed driving method and key waveforms. (a) Schematic diagram of EEFL backlight for a 17-inch LCD TV. (b) A trapezoidal wave full-bridge inverter with a transformer. (c) Equivalent circuit. (d) Proposed driving scheme.

Mode 1 (t0 ≤ t < t1): As shown in Fig. 7 (d), the switch X_L is turned off at t0 by a zero current switching condition and three switches (X_H, Y_H, Y_L) are sustained to 0V. During Mode 1, VXY and VO go up from 0V toward VDC and n⋅VDC, respectively, with the help of the back electromotive force (BEMF) occurred in the secondary since the switch Y_H was turned off in Mode 8, and also by the aid of the self discharge by the wall charges accumulated on the glass surface by previous discharge in Modes 6 and 7. In this mode, all switches in the primary side are off and there is no initial current. Therefore, the primary side forms open circuit and the discharge current flows through the self-inductance on the secondary side of the transformer. The secondary voltage (VO) and current (IO) can calculated as below

( ) ⎥⎦

⎤⎢⎣

⎡−

⋅−+−⋅= −

− )(sin/1)(cos 000 ttRCttReItV dd

Ed

tO ω

ωαωα (1)

( ) ⎥⎦

⎤⎢⎣

⎡−−−⋅= −

− )(sin)(cos 000 tttteItI dd

dt

O ωωαωα (2)

where, ),2/( 2LR=α 2

2 )/(1 αω −= Ed CL , R = R2 + RE

≈ RE (Assume RE >> R2), R2 = winding resistance on the secondary side of the transformer, RE = resistance of EEFLs, CE = capacitance of EEFLs, L2 = self-inductance on the secondary side, I0- = initial current at the beginning of Mode 1.

Mode 2 (t1 ≤ t < t2): Mode 2 begins when the switch Y_L is turned on at t1 by a ZCS condition. Also, the switches X_H, Y_H, X_L are still off. During this mode, VO almost reaches n⋅VDC and induces the primary voltage VXY. Here, the main discharge and light emission start, but there is no current flow measured in primary side, as shown in Fig. 10, while the current (IO) consists of the displacement and discharge currents. The discharge by BEMF without power consumption in this mode helps the luminous efficiency increase. Thus, it is noted that the interval (Δt = t2− t1) between t2 and t1 is a critical factor which determines the luminous efficiency and the heat loss of the transformer. Therefore, Δt should be carefully tuned to reach the maximum efficiency by reducing the power consumption.

Mode 3 (t2 ≤ t < t3): At t2, the switch X_H is turned on and the switch Y_L is still on. During Mode 3, the inverter starts to supplies an electric energy to EEFLs in the path of VDC-X_H-Y_L-0V, so the primary transformer current (IXY) linearly increases, while the secondary current (IO) of the transformer goes down. Here, the discharge becomes weak and finally ends up by the wall charge accumulation. This mode should be carefully designed because of less light outputs and sudden floods

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T.-S. Cho et al.: A Low-Temperature Driving Scheme of EEFLs Inverter for LCD TV Backlights 703

of the primary current, and also has enough length to accumulate sufficient wall charges for the stable operation of next discharge in mode 6. In this mode, IXY, VO, and IO are given below

( ) [ ] )(1 21

)(

1

21 ttL

VeR

VtI DCttDCXY −≈−= −−α (3)

( ) DCO VntV ⋅= (4)

( ) ⎥⎦

⎤⎢⎣

⎡−−−⋅= −

− )(sin)(cos 22

202 tttteItI d

dd

tO ω

ωα

ωα (5)

where, ,/ 111 LR=α ),2/( 22 leakE LR=α 222 )/(1 αω −= Ed CL , VDC = DC-link voltage of the

inverter, R1 = winding resistance on the primary side of the transformer, L1eak2 = leakage inductance on the secondary side, L1 = self-inductance on the primary side, L2 = self-inductance on the secondary side, I0- = initial current at the beginning of Mode 3.

Mode 4 (t3 ≤ t < t4): Mode 4 initiates when the switch X_H is turned off at t3 and the switch Y_L is in on state. At the moment when the X_L is turned off, the BEMF starts to be induced. During this mode, VO decreases from n⋅VDC to 0V and the current (IO) flows into the

secondary side of the transformer by the BEMF. In this mode, VO, and IO are derived as

( ) )(sin 3tteLnVtI tDC

O −⋅−= −σ

α

σσ

ωω

(6)

( ) ⎥⎦

⎤⎢⎣

⎡−−−⋅= − )(sin)(cos 33 ttttenVtV t

DCO σσ

σα ω

ωαω (7)

where, ),2/( σα LR= ,/ 1

22 mLMLL −=σ R = R2 + RE ≈

RE, M = mutual inductance of the transformer, Lm1 = magnetizing inductance on the primary side.

Mode 5 (t4 ≤ t < t5): The switch Y_L is turned off at t4 under a zero current switching. In Mode 5, VO goes down from 0V toward −n⋅VDC and the current (IO) conducts by both the BEMF and the wall charges accumulated at both ends of the EEFLs. In this mode, VO, and IO are similar to equations (1) and (2) except for opposite direction.

Mode 6 (t5 ≤ t < t6): Mode 6 is analogous to Mode 2. When the switch X_L is turned on at t5 by a ZCS condition, Mode 6 starts. Three switches X_H, Y_H, Y_L are still off through this interval. In this mode, the lights are emitted by the main discharge current (IO).

Mode 7 (t6 ≤ t < t7): As similar to Mode 3, the switch Y_H is turned on at t6 while the switch X_L is on throughout this mode. During this mode, an electric

(a) (b) (c) (d)

(e) (f) (g) (h)

Fig. 8. Operational mode diagrams of EEFLs inverter. (a) Mode 1. (b) Mode 2. (c) Mode 3. (d) Mode 4. (e) Mode 5. (f) Mode 6. (g) Mode 7. (h) Mode 8.

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energy is supplied to the lamps via the path VDC-Y_H-X_L-0V. In the mode, the primary transformer current (IXY) linearly increases to the negative direction.

Mode 8 (t7 ≤ t < t8): At t7, the switch Y_H is turned off, while the switch X_L is still on. During Mode 8, VO rises from −n⋅VDC to 0V and the current (IO) circulates into the EEFLs by the aid of the BMEF. After that, Mode 1 is repeated.

III. EXPERIMENTAL RESULTS To investigate the feasibility of the proposed driving

scheme, experiments have been performed using a prototype 17-inch LCD TV backlight unit with 12 EEFLs. Table I shows the system parameters used in this experiment.

Fig. 9 shows the Q-V Lissajous figure [6] to calculate the capacitance (CE) of EEFLs. In Fig. 9, the values of the Q-V figure can be obtained by analyzing the wall charges accumulated on the inner glass and the voltage applied to the lamps. As expected, the slope of the Q-V diagram represents the capacitance of EEFLs, i.e., CE = ΔQ/ΔV. In [4], it has been reported that a self-discharge synchronizing point is determined by the switching frequency and has much better performance in brightness and efficiency. In this paper, the switching frequency (fs) has been chosen as 50 kHz to realize the self-discharge synchronizing operation.

TABLE I SYSTEM PARAMETERS

DC-link Voltage VDC = 24 V Peak Voltage Applied to EEFLs VO = 1200 V

Turn Ratio 8 : 400 Self-Inductance L1 = 0.035 mH

Leakage Inductance Lleak1 = 0.29 μH Primary Winding Resistance R1 = 0.27 Ω

Self-Inductance L2 = 84.55 mH Leakage Inductance Lleak2 = 2.23 mH

Transformer

Secondary Winding Resistance R2 = 204.5 Ω

Capacitance of 12 EEFLs CE = 125 pF Switching Frequency fs = 50 kHz

Fig. 9. Q-V Lissajous figure to calculate CE.

Fig. 10 shows the experimental results of the proposed driving method shown in Fig. 7 (d). The waveforms in Fig. 10 (a) show the secondary voltage (VO) and primary/secondary currents (IXY, IO) of the transformer, respectively. Fig. 10 (b) shows the primary and secondary voltages (VY, VO) and currents (IXY, IO) of the transformer and gating signals of power switches (Y_L, Y_H, X_L), respectively. In Fig. 10 (b), the interval (Δt = t2− t1) between t2 and t1 was observed as about 3.2 μs. It is noticed that the gating signal (Y_H) is measured with respect to ground level.

(a)

(b)

Fig. 10. Experimental results for proposed driving method. (a) Secondary voltage (VO) and primary/secondary currents (IXY, IO) of the transformer. (b) Primary and secondary voltages (VY, VO) and currents (IXY, IO) of the transformer and gating signals of power switches.

Fig. 11 shows the transformer temperature comparison according to the interval (Δt) between t2 and t1. As shown in Fig. 11, it is noted that the temperature of the

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T.-S. Cho et al.: A Low-Temperature Driving Scheme of EEFLs Inverter for LCD TV Backlights 705

transformer is dramatically decreased and hits the bottom when Δt is 3.2 μs. After that point, the variation of the temperature is reduced. It means that the maximum efficiency of the transformer is derived at that time because most power loss is consumed at the transformer.

Fig. 11. Transformer temperature comparison according to Δt (= t2−t1).

Fig. 12 shows the brightness and luminous efficiency versus the interval (Δt) between t2 and t1. The luminous efficiency (η) is defined as following.

]/[ WlmP

BA ⋅⋅=πη (8)

where, A = area of display, B = brightness, P = electric power.

Fig. 12. Brightness and efficiency comparison according to Δt (= t2−t1).

It is clearly seen that the brightness and luminous efficiency have the maximum values at the same point described in Fig. 11. This characteristic explains that the large amount of power is consumed for heating the transformer at the smaller cases than the optimum Δt. As Δt increases over 3.2 μs, the power loss at the transformer is reduced because the length of Mode 3, which consumes most of power caused by the floods of the primary current, is shortened. Also, an insufficient amount of the wall charge accumulated in shorter Mode 3 results in weak discharge and less light output in next main discharge as described in Fig. 8 (f).

IV. CONCLUSION A new low-temperature trapezoidal wave driving scheme of

EEFLs inverter for LCD TV backlights has been proposed to reduce the temperature of the transformer. In this paper, the proposed driving method accomplishes the zero current switching (ZCS) when the lower switches are turned off and on. Furthermore, the Q-V Lissajous analysis method has been used to derive the capacitance of EEFLs, and the optimal switching interval for a low temperature of the transformer has been determined. Consequently, the proposed technique can improve the system efficiency by lowering the temperature of the transformer which consumes most power loss.

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Tae-Seung Cho (M’08) received the B.S., M.S. and Ph.D. degrees from Kwangwoon University, Seoul, Korea, in 1995, 1998, and 2002, respectively. From 2002 to 2003, he was with Stevens Institute of Technology, Hoboken, NJ, as research scholar, where he worked on the applications of dielectric barrier discharge and capillary discharge. From 2003 to 2005, he was a senior engineer in Plasmion Corporation, Hoboken, NJ, where his research concern was the capillary plasma application for

surface modification and flat panel display. Since 2005, he has been with the R&D Center and PDP Development Team, Samsung SDI Co., Ltd., Korea, as a senior engineer. His current research fields are in plasma diagnostics, microplasma applications, dielectric barrier discharge, plasma display panels and LCD backlights.

Jin-Woo Jung (S’97–M’06) received the B.S. and M.S. degrees in Electrical Engineering from Hanyang University, Seoul, Korea in 1991 and 1997, respectively, and the Ph.D. degree in Electrical and Computer Engineering from The Ohio State University, Columbus, Ohio, in 2005. From 1997 to 2000, he was with the Digital Appliance Research Laboratory, LG Electronics Co., Ltd., Seoul, Korea. From 2005 to 2008, he worked at the R&D Center and PDP Development Team, Samsung SDI Co., Ltd., Korea, as a senior

engineer. Since 2008, he has been an Assistant Professor with the Department of Electrical Engineering, Dongguk University, Seoul, Korea. His current research interests are in the area of driving circuits and driving methods of liquid crystal displays (LCD) and ac plasma display panels (PDP), control of distributed generation systems using renewable energy sources, fuel cell systems, electric machine drives, design and control of power converters.

Dong-Myung Lee (S’01-M’06) received the B.S. and M.S. degrees in Electrical Engineering from Hanyang University, Seoul, Korea, in 1994 and 1996, respectively, and the Ph. D. degree in Electrical and Computer Engineering from the Georgia Institute of Technology, Atlanta, Georgia in 2004. From 1996 to 2000, he worked in the LG Electronics Inc., Seoul, Korea. From 2004 to 2007, he was employed by the Samsung SDI R&D

Center, Yongin, Korea, as a Senior Engineer. From 2007 to 2008, he was with the department of electrical engineering, Hanyang University, as a Research Professor. Since 2008, he has been the Faculty of the School of Electronics and Electrical Engineering at Hongik University, Seoul, Korea. His research interests and experience include driving systems for LCD and PDP, power converters, power quality compensation devices, and variable speed drives.

Eun Ha Choi (M’96) received the B.S. degree from Seoul National University, Seoul, Korea, in 1982 and the M.S. and Ph.D. degrees from the Korea Advanced Institute of Science and Technology, Seoul, in 1984 and 1987, respectively. From 1988 to 1989, he was with the Naval Surface Warfare Center, Silver Spring, MD, where he was a post doctorate and worked on the magnetic conditioning of the intense electron beam, time-resolved electron-beam measurements, and high-

power microwave generation from the custron device. From 1989 to 1990, he was an Assistant Professor/Contractor with the Department of Physics, Hampton University/NASA, Hampton, VA, where his research concern was the high power inverse pinch plasma switch for the plasma thruster. From 1990 to 1992, he was a Senior Research Scientist with the Korea Research Institute of Standards and Science, where he studied plasma diagnostics and plasma processing technology. Since 1992, he has been with Kwangwoon University, Seoul, where he is currently a Professor with the Charged Particle Beam and Plasma Laboratory/PDP Research Center, Department of Electrophysics. Since 1997, he has also been the Chairman of the PDP Research Center, Kwangwoon University. From 2001 to 2003, he was a Professor with Texas Tech University, Lubbock, where he worked on high-power microwave generation from the virtual cathode oscillator. His current research fields are in high-power charged particle beams and plasmas from pulsed systems, plasma-material processing, focused ion-beam physics and technology, and plasma display panels.

Guangsup Cho received the B.S. degree from Seoul National University, Seoul, Korea, in 1980 and the M.S. and Ph.D. degrees from the Korea Advanced Institute of Science and Technology, Seoul, in 1983 and 1987, respectively, where his work involved MHD stability analysis in general toroidal geometry. From 1992 to 1993, he was with MIT Research Laboratory of Electronics, Cambridge, MA, where he worked on ion-beam lithography. Since 1988, he has been with

Kwangwoon University, Seoul, Korea, where he is currently a Professor in the Charged Particle Beam and Plasma Laboratory/PDP Research Center, Department of Electrophysics. His current research fields are in electron and ion-beam lithography, focused ion beam, plasma display panels, and LCD backlights.

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