• 한국조명전기설비학회지:조명전기설비
• /
• 제8권3호
• /
• pp.36-43
• /
• 1994

본 연구는 교류전원측에서 콘버터에 의해 출력전압조정과 동시에 입력전류가 전압과 동상에 가까운 정현파가 되도록 하기 위해 고주파 스위칭에 의한 단상 부스터 콘버터의 제어방식을 분석하고 가변밴드폭 제어방식에 의해 1[kW]부하에 대하여 각 파라메타를 산정하며 실험장치를 구성하여 주파수 스팩트럼 분석기에 의한 분석을 토대로 고역률 동작을 확인하고자 한다.

• 전력전자학회논문지
• /
• 제18권5호
• /
• pp.501-506
• /
• 2013

A hold-up time compensation circuit is proposed to get high efficiency of the front-end phase-shifted full bridge DC/DC converter. The proposed circuit can make the phase-shifted full bridge front-end DC/DC converter built with 0.5 duty ratio so that the conduction loss of the primary side and voltage stress across rectifier in the secondary side are reduced and the higher efficiency can be obtained. Furthermore, the requirement of an output filter significantly can diminish due to the perfect filtered waveform. A 12V/100A prototype has been made and experimental results are given to verify the theoretic analysis and detailed features.

• Electronic Materials Letters
• /
• 제14권6호
• /
• pp.774-783
• /
• 2018

Full maximum-entropy mobility-spectrum analysis (FMEMSA) is the best algorithm among mobility spectrum analyses by which we can obtain a set of partial-conductivities associated with mobility values (mobility spectrum) by analyzing magnetic-field-dependent conductivity-tensors. However, it is restricted to a direct band-gap semiconductor and should be modified for materials with other band structures. We developed the modified version of FMEMSA which is appropriate for a material with a single anisotropic valley, or an indirect-band-gap semiconductor quantum-well with a single non-degenerate conduction-band valley e.g., (110)-oriented AlAs quantum wells with a single anisotropic valley. To demonstrate the reliability of the modified version, we applied it to several sets of synthetic measurement datasets. The results demonstrated that, unlike existing FMEMSA, the modified version could produce accurate mobility spectra of materials with a single anisotropic valley.

• Bulletin of the Korean Chemical Society
• /
• 제16권10호
• /
• pp.929-933
• /
• 1995

The electronic band structure and electrical properties of KMo4O6 containing chains of condensed molybdenum octahedra are analyzed by means of the extended Hu&ckel tight-binding method. KMo4O6 has partially filled bands of 1D as well as 3D character. They also exhibit the anisotropic band dispersions with bandwidths much larger along the c* axis than along the directions perpendicular to it. Thus, conduction electrons are essentially delocalized along the c* direction (i.e., the chain of condensed molybdenum octahedra) in the solid. The 1D band of two partially filled d-block bands leads to Fermi surface nesting with the wave vector q=0.3c*. The CDW instability due to this nesting is expected to cause the phase transition associated with the resistivity anomaly at low temperature. The characteristics of metallic behavior in the crystallographic ab plane are explained on the basis of the unnested 2D Fermi surfaces.

• ETRI Journal
• /
• 제41권1호
• /
• pp.124-132
• /
• 2019

The energy balance (EB) model of a primary side regulation (PSR) fly-back converter in the discontinuous conduction mode (DCM) is discussed in this paper. Based on this EB model, the stability of a PSR fly-back converter in the pulse skipping mode (PSM) is analyzed, and a self-adapting modulation factor control strategy is proposed. Theoretical analysis and simulation results show that by saving an optocoupler and correlative circuits, which are necessary in traditional PSM fly-back converters, the modulation factor tolerance controlled by this method is 1.26% on average, corresponding to the ideal value. Compared with traditional fly-back PSM controllers, the power saved in the sampler/comparator modules is 87% on average for a load range of $1{\Omega}$ to $1k{\Omega}$.

• 한국정보통신학회:학술대회논문집
• /
• 한국정보통신학회 2014년도 추계학술대회
• /
• pp.765-768
• /
• 2014

본 연구에서는 비대칭 이중게이트 MOSFET의 상하단 게이트 산화막 두께 비에 대한 문턱전압 및 전도중심의 변화에 대하여 분석하고자한다. 비대칭 이중게이트 MOSFET는 상하단 게이트 산화막의 두께를 다르게 제작할 수 있어 문턱전압이하 영역에서 전류를 제어할 수 있는 요소가 증가하는 장점이 있다. 상하단 게이트 산화막 두께 비에 대한 문턱전압 및 전도중심을 분석하기 위하여 포아송방정식을 이용하여 해석학적 전위분포를 구하였다. 이때 전하분포는 가우스분포함수를 이용하였다. 하단게이트 전압, 채널길이, 채널두께, 이온주입범위 및 분포편차를 파라미터로 하여 문턱전압 및 전도중심의 변화를 관찰한 결과, 문턱전압은 상하단 게이트 산화막 두께 비에 따라 큰 변화를 나타냈다. 특히 채널길이 및 채널두께의 절대값보다 비에 따라 문턱전압이 변하였으며 전도중심이 상단 게이트로 이동할 때 문턱전압은 증가하였다. 또한 분포편차보단 이온주입범위에 따라 문턱전압 및 전도중심이 크게 변화하였다.

• Bulletin of the Korean Chemical Society
• /
• 제20권3호
• /
• pp.337-340
• /
• 1999

Luminescence of bismuth activated CaS, CaS:Bi, prepared in sodium polysulfide is studied. Excitation spectrum of CaS:Bi shows a band at 350 nm due to the recombination process between holes in Na+Ca2+ and electrons in conduction bands, in addition to bands at 260 nm from band gap of CaS, and at 320 nm (1S0→1P1) and at 420 nm (1S0→3P1) from electronic energy transitions of Bi. Emission band at 450 nm is from 3P1→1S0 transition of Bi3+, bands at 500 nm and 580 nm correspond to recombinations of electron donors (Bi3+Ca2+ and VS2-) with acceptors (VCa2+ and Na+Ca2+). Emission band of 3P1→1S0 transition is shifted to longer wavelength from CaS:Bi to BaS:Bi, due to the increase of the Stokes shift by the decrease of the crystal field parameter from CaS:Bi to BaS:Bi.

• 전력전자학회논문지
• /
• 제27권2호
• /
• pp.134-141
• /
• 2022

This study presents a method for reducing current distortion that occurs when a dual-buck inverter generates reactive power. Dual-buck inverters, which are only capable of unity power factor operation, can generate reactive power capabilities by modifying a modulation technique. However, under non-unity power factor conditions, current distortion occurs at zero-crossing points of grid voltage and output current. This distortion is caused by parasitic capacitors, dead-time, and discontinuous conduction mode operation. This study proposes a modified modulation method to alleviate the current distortion at zero-crossing point of the grid voltage. A repetitive controller is applied to reduce this distortion of the output current. A 1 kVA prototype is built and tested. Simulation and experimental results demonstrate the effectiveness of the proposed method.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
• /
• pp.299-299
• /
• 2016

SiC는 넓은 에너지갭 (Eg=~3.4 eV)을 갖는 반도체로써, 고전압, 고온에서 동작이 가능하여 기존의 Si기반의 파워디바이스를 대체하기 위한 물질로 많은 연구가 이루어지고 있다. 파워 디바이스의 성능 향상을 위해서는 기판과 절연체 사이의 계면에 생성되는 계면 결함을 감소시켜야 한다. 따라서 본 연구에서는 SiC 기판에 high-k 물질인 HfO2를 증착하여 HfO2/SiC 계면에 유도된 결함을 분석하고 이를 감소시킬 수 있는 방법에 대한 연구를 수행하였다. HfO2 박막은 atomic-layer-deposition (ALD) 방법을 이용하여 SiC 기판 위에 $200^{\circ}C$에서 증착하였다. HfO2 박막 증착 후 NH3 분위기에서 rapid thermal annealing 방법을 이용하여 $600^{\circ}C$에서 1분 동안 열처리 진행하였다. Current-voltage (I-V) 측정을 통해 열처리 전 HfO2/SiC의 절연파괴 전압이 약 8.3 V 임을 확인하였다. NH3 열처리 후 HfO2/SiC의 절연파괴 전압이 10 V로 증가하였으며 누설 전류가 크게 감소하는 것을 확인하였다. 또한 capacitance-voltage (C-V) 측정을 통해 열처리 후 flat band voltage가 negative 방향에서 positive 방향으로 이동함을 확인하였고, 이를 통해 NH3 열처리 방법이 HfO2/SiC 계면에 존재하는 결함을 감소시킬 수 있음을 확인하였다. 전자 구조상의 conduction band edge에 존재하는 결함 준위를 분석하기 위해 x-ray absorption spectroscopy (XAS) 분석을 실시하였고, 열처리 전 HfO2/SiC 계면에 많은 결함 준위가 존재함을 확인하였으며, x-ray photoelectron spectroscopy (XPS) 분석을 통해 이 결함 준위가 oxygen deficiency state과 관련됨을 알 수 있었다. NH3 열처리 후 결과와 비교해보면, oxygen deficiency state가 감소함을 확인하였으며 이로 인해 conduction band edge에 존재하는 결함 준위가 감소함을 알 수 있었다. 따라서, NH3 열처리 방법을 이용하여 HfO2/SiC 계면에 존재하는 결함을 감소시킬 수 있으며, HfO2/SiC의 물리적, 전기적 특성을 향상시킬 수 있다는 결과를 도출하였다.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
• /
• pp.246-246
• /
• 2016

Tungsten-nitrogen (W-N) co-doping has been known to enhance the photocatalytic activity of anatase titania nanoparticles by utilizing visible light. The doping effects are, however, largely dependent on calcination or annealing conditions, and thus, the massive production of quality-controlled photocatalysts still remains a challenge. Using density functional theory (DFT) thermodynamics and time-dependent DFT (TDDFT) computations, we investigate the atomic structures of N doping and W-N co-doping in anatase titania, as well as the effect of the thermal processing conditions. We find that W and N dopants predominantly constitute two complex structures: an N interstitial site near a Ti vacancy in the triple charge state and the simultaneous substitutions of Ti by W and the nearest O by N. The latter case induces highly localized shallow in-gap levels near the conduction band minimum (CBM) and the valence band maximum (VBM), whereas the defect complex yielded deep levels (1.9 eV above the VBM). Electronic structures suggest that substitutions of Ti by W and the nearest O by N improves the photocatalytic activity of anatase by band gap narrowing, while defective structure degrades the activity by an in-gap state-assisted electron-hole recombination, which explains the experimentally observed deep level-related photon absorption. Through the real-time propagation of TDDFT (rtp-TDDFT), we demonstrate that the presence of defective structure attracts excited electrons from the conduction band to a localized in-gap state within a much shorter time than the flat band lifetime of titania. Based on these results, we suggest that calcination under N-rich and O-poor conditions is desirable to eliminate the deep-level states to improve photocatalysis.