• Journal of Power Electronics
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• v.6 no.1
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• pp.73-82
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• 2006

Plasma display panels (PDPs) have a serious thermal problem, because the luminance efficiency of a conventional PDP is about 1.5 1m/W and it is less than $3\~5\;lm/W$ of a cathode ray tube (CRT). Thus there is a need for improving the luminance efficiency of the PDP. There are several approaches to improve the luminance efficiency of the PDP and we adopted a driving PDP at high frequency range from 400kHz up to over 700kHz. Since a PDP is regarded as an equivalent inherent capacitance, many types of sustaining drivers have been proposed and widely used to recover the energy stored in the PDP. However, these circuits have some drawbacks for driving PDPs at high frequency ranges. In this paper, we investigate the effect of the parasitic components on the PDP itself and on the driver when the reactive energy of the panel is recovered. Various drivers are classified and evaluated based on their suitability for high frequency drivers. Finally, a current-fed driver with a DC input voltage bias is proposed. This driver overcomes the effect of parasitic components in the panel and driver. It fully achieves a ZVS of all full-bridge switches and reduces the transition time of the panel polarity. It is tested to validate the high frequency sustaining driver and the experimental results are presented.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.380-384
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• 2005

Plasma display panel (PDP) has a serious thermal problem, because the luminance efficiency of the conventional PDP is about 1.5 lm/W and it is less than $3{\sim}5$ lm/W of cathode ray tube (CRT). Thus there is a need for improving the luminance efficiency of the PDP There are several approaches to improve the luminance efficiency of the PDP and we adopt the driving PDP at high frequency range from 400 kHz up to over 700 kHz. Since a PDP is regarded as an equivalent inherent capacitance, many types of sustaining drivers have been proposed and widely used to recover the energy stored in the PDP. However, these circuits have some drawbacks for driving PDP at high frequency range. In this paper, we investigate the effect of the parasitic components of PDP itself and driver when the reactive energy of panel is recovered. Various drivers are classified and evaluated whether it is suitable for high frequency driver, and finally current-fed type with do input voltage biased is proposed. This driver overcomes the effect of parasitic component in panel and driver and fully achieves ZVS of all full-bridge switches and reduces the transition time of the panel polarity.

• Journal of the Korean Vacuum Society
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• v.17 no.4
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• pp.331-340
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• 2008

A method of measuring the current and voltage is suggested in the circuit of cold cathode fluorescent lamps (CCFLs) which are driven at a high frequency of $50{\sim}100\;kHz$ and a high voltage of several kV. It is difficult to measure the current and voltage in the lamp circuit, because the impedance of the probe at high voltage side causes the leakage current and the variation of luminance. According to the analysis of equivalence circuit with the probe impedance and leakage current, the proper measuring method is to adjust the input DC voltage and to keep the specific luminance when the probe is installed at a high voltage circuit. The lamp current is detected with a current probe or a high frequency current meter at the ground side and the voltage is measured with a high voltage probe at the high voltage side of lamp. The lamp voltage($V_C$) is measured between the ballast capacitor and the lamp electrode, and the output voltage($V_I$) of inverter is measured between inverter output and ballast capacitor. As the phases of lamp voltage($V_C$) and current ($I_G$) are nearly the same values, the real power of lamp is the product of the lamp voltage($V_C$) by the lamp current($I_G$). The measured value of the phase difference between inverter output voltage($V_I$) and lamp current($I_G$) is appreciably deviated from the calculated value at $cos{\theta}=V_C/V_I$.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.679-682
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• 2007

We have developed low voltage operating OLEDs with new electron transport layer. The device having a structure of ITO/2TNATA/HTL:Rubrene(1%)/HTL /new ETL/LiF/Al have been used. The voltage for achieving $1,000\;cd/m^2$ was 4.1 V, whereas the turn on voltage for the brightness of $1\;cd/m^2$ was 2.8 V. This high luminance at low operating voltage is caused by the high current density, resulting from high electron conduction property of the new electron transport layer.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.34-36
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• 2008

Highly efficient red and green phosphorescent devices comprising a simple bilayer structure are reported. The driving voltage to reach $1000\;cd/m^2$ is 4.5 V in $Bebq_2:\;Ir(piq)_3$ red phosphorescent device. Current and power efficiency values of 9.66 cd/A and 6.90 lm/W in this bi-layered simple structure PHOLEDs are obtained, respectively. While in $Bepp_2:Ir(ppy)_3$ green phosphorescent device, the operating voltage value of 3.3V and current and power efficiencies of 37.89 cd/A and 35.02 lm/W to obtain a luminance of $1000\;cd/m^2$ are noticed, respectively.

• Transactions on Electrical and Electronic Materials
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• v.5 no.1
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• pp.24-28
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• 2004

We have used ITO/Alq$_3$/Al structure to study electrical conduction mechanism in organic light-emitting diodes. Current-voltage-luminance characteristics were measured at room temperature by varying the thickness of Alq$_3$ layer from 60 to 400mm. We were able to confirm that there are three different mechanisms depending on the applied voltage region; ohmic, space-charge-limited current, and trap-charge-limit-current mechanism. And the maximum luminous efficiency was obtained when the thickness of Alq$_3$ layer is 200nm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.537-538
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• 2005

A way of measuring an efficiency of organic light-emitting diodes are studied. The efficiency is obtained from the current-voltage-luminance characteristics of the devices. Basically, number of charge carriers are obtained from the current-voltage characteristics, and the number of photons are obtained from the current of Si-photodetector. The organic light-emitting diodes are assumed as a lambertian light source and a program is made for calculating the efficiency. A device structure of ITO/TPD/$Alq_3$/Al is manufactured using thermal-vapor evaporation. This device is set into a measuring system and measured the efficiency. The efficiencies are measured using the lab-made program and commercially available equipments. The obtained values are similar to each other within 10% uncertainty.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.4
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• pp.397-402
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• 2023

We have developed inverted green phosphorescent organic light emitting diodes (OLEDs) using 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and bis(carbazole-9-yl)biphenyl (CBP) hole transport layers. The driving voltage, current efficiency, power efficiency, and emission characteristics of devices were investigated. While the driving voltage for the same current density was about 1~2 V lower in the devices with the TAPC layer, the maximum luminance was higher in the device with the CBP layer. The maximum current efficiency and power efficiency were 3.2 and 2.7 times higher in the device with the CBP layer, respectively. The higher efficiency in the CBP device resulted from the enhanced hole-electron balance although weak parasitic recombination takes place in the CBP hole transport layer.

• Proceedings of the KIEE Conference
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• 2006.10a
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• pp.222-223
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• 2006

In this paper, we manufactured high flux LED module with Through Hole type. and we measured electrical, optical and thermal properties by driving type. LED module was composed with 8*8 arrangement form by using the glass epoxy PCB. Also, we measured the most suitable driving type with static voltage driving type and static current driving type. As a result, the LED Module of static voltage driving type showed high luminance characteristic than the static current driving type by suppling enough bias. However, the static current driving type showed more stable driving properties because of fast decreasing properties about brightness by increasing the surrounding temperature in the static voltage driving type. Also, due to Quantum confined Stark effect from piezoelectric field, the wavelength of bule peak shifted to long wavelength direction by increasing the surrounding temperature in the static voltage driving type.

• Journal of Korea Society of Industrial Information Systems
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• v.20 no.6
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• pp.29-36
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• 2015

This paper presents an LED backlight driver IC consisting of three linear current regulators and an output-voltage regulation loop with a self-adjustable reference voltage. In the proposed LED driver, the output voltage is controlled by dual feedback loops. The first loop senses and controls the output voltage, and the second loop senses the voltage drop of the linear current regulator and adjusts the reference voltage. With these feedback loops, the voltage drop of the linear current regulator is maintained at a minimum value, at which the driver efficiency is maximized. The output of the driver is a three-channel LED setup with four LEDs in each channel. The luminance is adjusted by the PWM dimming signal. The proposed driver is designed by a $0.35-{\mu}m$ 60-V high-voltage process, resulting in an experimental maximum efficiency of approximately 85%.