• 조명전기설비학회논문지
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• 제24권6호
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• pp.138-146
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• 2010

본 논문은 직류 전기철도 급전시스템에서 레일전위와 누설전류의 분석 기법을 제시하였다. 일반적으로 직류 전기철도 급전시스템에서는 운행용 레일을 귀로 전류(부극성)의 도체로 사용하고 있으므로 레일전위가 발생하고, 특히 차량 운행용 레일과 대지사이의 저항이 작은 경우에는 대지로 흐르는 누설전류가 문제가 된다. 이 레일전위 및 누설전류는 레일 주변에 설치된 지하 매설물에 영향을 미치며, 인체의 안전과도 관련이 있다. 이에 따라 직류 전기철도 급전시스템에서 레일전위와 누설전류를 억제하는 것은 전기철도 주변 환경 및 안전 측면에서 중요한 문제이다. 이상과 같은 관점에서, 직류 전기철도 급전시스템에 대하여 단독급전 및 병렬급전 상황에서 레일전위와 누설전류를 계산할 수 있는 알고리즘을 제안하였으며, 또한 열차주행시뮬레이션(TPS)과 연동하여 열차주행에 따라 부하전류가 변동되는 상황에서 레일전위와 누설전류를 정량적으로 분석할 수 있도록 하였다. 제안한 알고리즘을 이용하여 시뮬레이션 프로그램을 개발하였고, 직류전기철도 급전시스템에 대하여 사례 연구를 수행하였다.

• 공업화학
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• 제19권6호
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• pp.640-644
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• 2008

저온 플라스마 공정을 이용하여 알루미늄 표면에 묻은 윤활유를 세정하였다. 아르곤이 혼합된 산소 플라스마를 사용하였으며, 아르곤의 혼합비, 방전전력, negative DC potential 등의 공정변수를 변화시키면서 실험을 수행하였다. 저온 플라스마 세정 후 케이스의 표면을 FTIR과 EDX를 사용하여 분석한 결과 순수 윤활유의 경우 대부분이 20 min 안에 제거되었다. 제거효율은 저온 플라스마 공정조건에 따라 크게 달라졌으며, 산소에 아르곤이 약 30% 혼합된 기체를 사용하여 케이스에 -500 V 이상의 negative DC potential을 걸어주고 300 W로 처리할 때 가장 높은 효율을 보였다. 하지만, 무기물이 함유된 윤활유의 경우에는 어떤 조건에서도 60% 이상의 제거효율을 얻을 수 없었다.

• Journal of Power Electronics
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• 제14권2호
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• pp.203-216
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• 2014

In the conventional dc-dc converter, a pair of additional diode and the adjacent passive component capacitor/inductor can be added to the circuit with an X-shape connection, which generates a family of new topologies. The novel circuits, also called diode-assisted dc-dc converter, enhance the voltage boost/buck capability and have a great potential for high step-up/step-down power conversions. This paper mainly investigates and compares conventional dc-dc converter and diode-assisted dc-dc converter in wide range power conversion from the aspects of silicon devices, passive components requirements, electro-magnetic interference (EMI) and efficiency. Then, a comprehensive comparison example of a high step-up power conversion system was carried out. The two kinds of boost dc-dc converters operate under the same operation conditions. Mathematical analysis and experiment results verify that diode-assisted dc-dc converters are very promising for simultaneous high efficiency and high step-up/step-down power conversion in distributed power supply systems.

• 한국진공학회지
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• 제2권4호
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• pp.501-506
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• 1993

The spatial potential distribution of electron cyclotron resonance plasma is measured as a function of tehsubstrate DC bias by Langmuir probe method. It is observed that the substrate DC bias changes the slope of the plasma potential near the subsrate, resulting in changes in flux and energy of the impinging ions across plasma $_strate boundary along themagnetric field. The effect of the substrate DC bias on the low-temperature silicon homoepitaxy (below $560^{\circ}C$) is examine dby in situ reflection high energy electron diffraction (RHEED), cross-section transmission electron microscopy (XTEM),plan-view TEM and high resolution transmision electron microscopy(HRTEM). While the polycrystalline silicon layers are grow withnegative substrate biases, the single crystaline silicon layers are grown with negative substrate biases, the singel crystalline silicon layers are grown with positive substrate biases. As the substrate bias changes form negative to positive values, the growth rate decreases. It is concluded that the control of the ion energy during plasma deposition is very important in silicon epitaxy at low temperatures below $560^{\circ}C$ by UHV-ECRCVD.VD.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.29-32
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• 2000

In this paper, an analytical model for I-V characteristics of a HEMTs is Proposed. The developed model takes into account the temperature dependence of drain current. In high-speed ICs for optical communication systems and mobile communication systems, temperature variation affects performance; for example the gain, efficiency in analog circuits and the delay time, power consumption and noise mrgin in digital circuits. To design such a circuit taking into account the temperature dependence of the current-voltage characteristic is indispensible. This model based on the analytical relation between surface carrier density and Fermi potential including temperature dependent coefficients.

• 한국가시화정보학회지
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• 제9권4호
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• pp.22-27
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• 2011

In this study, we present methods of coupling a commercial code, ANSYS CFX, and the user Fortran codes for solving an unsteady electro-osmotic flow around a pair of electrodes, receiving DC, attached to the top and the bottom walls of a two-dimensional cavity. We developed a module of Fortran programs for solving the ion-transport equations as well as the Poisson equations for the potential to be used in coupling with the CFX. We present how the developed codes are applied to solving the transient DC electro-osmotic flow problem within a simple cavity. We also address various problems encountered during the development process and explain why such problems are raised.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 B
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• pp.1151-1153
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• 2004

In this paper, small-signal modeling and closed-loop performance of charge control employed to an asymmetrical half-bridge (ASHB) dc-to-dc converters are investigated. The charge control is selected as an alternative to the conventional voltage-mode control and peak current-mode (PCM) control, which have their respective limitations and problems when adapted to ASHB dc-to-dc converters. The current-loop dynamics of the charge control are presented in comparison with those of voltage-mode and PCM control. This paper demonstrates that the charge control offers better dynamic performance compared to voltage-mode control and superior noise characteristics compared to PCM control. The potential problem of charge control are also addressed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.1552-1553
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• 2011

The HVDC transformer which is one of the main equipments for HVDC(High Voltage Direct Current) electric power transmission systems is exposed to not only AC voltage but also the inflowing DC voltage which comes from the DC-AC converter systems. Therefore, the HVDC transformer insulation system is required to withstand the electric field stress under AC, DC and DC polarity reversal conditions. However the electric field distributions under those conditions are different because the AC electric field and DC electric field are governed by permittivity and conductivity, respectively. In this study, the changes of electric potential and electric field of conventional AC transformer insulation system under DC polarity reversal test condition were analyzed by FEM(Finite Element Method). The DC electric field stress was concentrated in the solid insulators while the AC electric field stress was concentrated in the mineral oil. In addition, the electric stress under that condition which is affected by the surface charge accumulation at the interfaces between insulators was evaluated. The stress in some parts could be higher than that of AC and DC condition, during polarity reversal test. The result of this study would be helpful for the HVDC transformer insulation system design.

• 한국정보통신학회논문지
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• 제12권3호
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• pp.517-526
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• 2008

본 논문에서는 자동차 계기판의 OLED 디스플레이 모듈용 One-chip DC-DC 변환기 회로를 제안하였다. 전하 펌핑 방식의 OLED 패널 구동전압 회로는 PWM(Pulse Width Modulation) 방식을 사용한 DC-DC 변환기 회로에 비해 소형화, 저가격 및 낮은 EMI 특성을 갖는다. 그리고 Bulk-potential 바이어싱 회로를 사용하므로 전하 펌핑 시 기생하는 PNP BJT에 의한 전하 손실을 방지하도록 하였고, 밴드갭 기준전압 발생기의 Start-up 회로에서 전류소모를 기존 BGR 회로에 비해 42% 줄였고 VDD의 링 발진기 회로에 로직전원인 VLP를 사용하여 링 발진기기 레이아웃 면적을 줄였다. 또한 OLED 구동전압인 VDD의 구동 전류는 OLED 패널에서 요구하는 40mA 이상이다. $0.25{\mu}m$ High-voltage 공정을 이용하여 테스트 칩을 제작 중에 있으며, 레이아웃 면적은$477{\mu}m{\times}653{\mu}m$이다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1998년도 하계종합학술대회논문집
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• pp.401-404
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• 1998

Recently, InGaP/GaAs HBTs have been much interested as a potential replacement for AlGaAs/GaAs HBTs because of their superior device and material properties. In this paper, DC characteristics of InGaP/GaAs HBTs and the temperature dependance as well as the reliability were investigated comparing with AlGaAs/GaAs HBTs. As a results InGaP/GaAs HBTs produced the superior performance to AlGaAs/GaAs HBTs.