• Journal of Power Electronics
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• 제17권4호
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• pp.1117-1126
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• 2017

The main contribution of this paper is the use of sensorless active diodes to generate the gate signals for a three-phase boost-rectifier with a self-powered control scheme. The sensorless operation is achieved making use of the gate control signals generated by the active diode schemes on each of the switching devices using a pulse width half-controlled boost rectifier modulation technique (PWM-HCBR). The proposed scheme synchronizes the gate control signals with a three phase voltage supply. Autonomous operation is obtained making use of the output DC bus to feed the control circuitry, the active diodes and the driver circuitry. The three-phase boost-rectifier is supplied by a three-phase permanent magnet electric generator powered by a solar concentrator dish with variable voltage and variable frequency conditions. Experimental results report an efficiency of up to 94.6% for 25 W and an input of 3.6 V peak per phase with 450.

• Journal of Power Electronics
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• 제19권2호
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• pp.353-362
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• 2019

To address the problem of circulating current loss in the traditional zero-current switching (ZCS) full-bridge (FB) DC/DC converter, a ZCS FB DC/DC converter topology and modulation strategy is proposed in this paper. The strategy can achieve ZCS turn on and zero-voltage and zero-current switching (ZVZCS) turn off for the primary switches and realize ZVZCS turn on and zero-voltage switching (ZVS) turn off for the auxiliary switches. Moreover, its resonant circuit power is small. Compared with the traditional phase shift full-bridge converter, the new converter decreases circulating current loss and does not increase the current stress of the primary switches and the voltage stress of the rectifier diodes. The diodes turn off naturally when the current decreases to zero. Thus, neither reverse recovery current nor loss on diodes occurs. In this paper, we analyzed the operating principle, steady-state characteristics and soft-switching conditions and range of the converter in detail. A 740 V/1 kW, 100 kHz experimental prototype was established, verifying the effectiveness of the converter through experimental results.

• Journal of Advanced Marine Engineering and Technology
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• 제41권1호
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• pp.70-75
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• 2017

본 논문에서는 MMIC (Monolithic microwave integrated circuit)상에서의 초소형 무선 통신 시스템에의 응용을 위해 주기적으로 배열된 다이오드를 이용한 전압제어형 전송선로(Voltage-controlled Artificial Transmission Line Employing Periodically Arrayed Diodes)의 RF특성 연구를 진행하였다. 연구 결과, 본 논문에서 제안하는 전압제어형 전송선로는 회로의 용량증가로 인해 기존의 마이크로스트립 선로의 35.2%로 단파장의 성능을 보여주었다. 그리고 유효유전율 및 전파상수는 기존의 마이크로스트립 선로보다 높은 결과를 나타냈으며, 감쇠정수 또한 기존의 전송선로에 비해 전압제어형 선로에서 높게 나타났다. 그리고 전압제어형 전송선로의 등가회로를 closed-form 방정식을 통하여 이론적으로 해석하였다.

• 폴리머
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• 제29권2호
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• pp.107-121
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• 2005

전기인광소자(electrophosphorescent light emitting diodes)의 경우 인광염료내에 있는 중금속에 의해 효과적인 전자 스핀-궤도 결합(spin-orbit coupling)이 가능하며, 이로 인해 일중항 여기자뿐만 아니라 삼중항 여기자로부터 발광이 가능하므로 이론적으로 $100\%$ 내부발광효율을 얻을 수 있다. 본 논문에서는 지난 몇 년 동안 본 연구실에서 진행한 고분자 호스트를 사용한 고분자 전기인광소자의 특성 및 에너지 전이 메커니즘에 대하여 기술하였다. 또한 고분자 전기인광소자에서의 상분리 및 응집현상이 고분자 호스트와 게스트인 인광염료간의 에너지 전이와 소자 특성에 미치는 영향을 규명하였다. 마지막으로 인광염료의 리간드에 치환체 도입 및 리간드 변화에 따른 전이금속화합물의 광학적, 전기적 특성 변화에 대하여 연구하였다.

• Tribology and Lubricants
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• 제21권6호
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• pp.268-271
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• 2005

In this study, the wear characteristics of five different dental composite resins cured by conventional halogen light and LED light sources were investigated. Five different dental composite resins of Surefil, Z100, Dyract AP, Fuji II LC and Compoglass were worn against a zirconia ceramic ball using a pin-on-disk type wear tester with 15N contact force in a reciprocal sliding motion of sliding distance of 10mm/cycle at 1Hz under the room temperature dry condition. The wear variations of dental composite resins were linearly increased as the number of cycles increased. It was observed that the wear resistances of these specimens were in the order of Dyract AP > Surefil > Compoglass > Z100 > Fuji II LC. On the morphological observations by SEM, the large crack formation on the sliding track of Fuji II LC specimen was the greatest among all resin composites. Dyract AP showed less wear with few surface damage. There is no significant difference in wear performance between conventional halogen light curing and light emitting diodes curing sources. It indicates that a light emitting diodes (LED) source can replace a halogen light source as curing unit for composite resin restorations.

• JSTS:Journal of Semiconductor Technology and Science
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• 제12권1호
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• pp.59-65
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• 2012

A study on the electrical characteristic analysis of solar cell diodes under experimental conditions of varying temperature and frequency has been conducted. From the current-voltage (I-V) measurements, at the room temperature, we obtained the ideality factor (n) for Space Charge Region (SCR) and Quasi-Neutral Region (QNR) of 3.02 and 1.76, respectively. Characteristics showed that the value of n (at SCR) decreases with rising temperature and n (at QNR) increases with the same conditions. These are due to not only the sharply increased SCR current flow but the activated carrier recombination in the bulk region caused by defects such as contamination, dangling bonds. In addition, from the I-V measurements implemented to confirm the junction uniformity of cells, the average current dispersion was 40.87% and 10.59% at the region of SCR and QNR, respectively. These phenomena were caused by the pyramidal textured junction structure formed to improve the light absorption on the device's front surface, and these affect to the total diode current flow. These defect and textured junction structure will be causes that solar cell diodes have non-ideal electrical characteristics compared with general p-n junction diodes. Also, through the capacitance-voltage (C-V) measurements under the frequency of 180 kHz, we confirmed that the value of built-in potential is 0.63 V.

• 한국전기전자재료학회논문지
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• 제19권9호
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• pp.818-824
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• 2006

The effects of high-temperature process required to fabricate the SiC devices on the surface morphology and the electrical characteristics were investigated for 4H-SiC Schottky diodes. The 4H-SiC diodes without a graphite cap layer as a protection layer showed catastrophic increase in an excess current at a forward bias and a leakage current at a reverse bias after high-temperature annealing process. Moreover it seemed to deviate from the conventional Schottky characteristics and to operate as an ohmic contact at the low bias regime. However, the 4H-SiC diodes with the graphite cap still exhibited their good electrical characteristics in spite of a slight increase in the leakage current. Therefore, we found that the graphite cap layer serves well as the protection layer of silicon carbide surface during high-temperature annealing. Based on a closer analysis on electric characteristics, a conductive surface transfiguration layer was suspected to form on the surface of diodes without the graphite cap layer during high-temperature annealing. After removing the surface transfiguration layer using ICP-RIE, Schottky diode without the graphite cap layer and having poor electrical characteristics showed a dramatic improvement in its characteristics including the ideality factor[${\eta}$] of 1.23, the schottky barrier height[${\Phi}$] of 1.39 eV, and the leakage current of $7.75\{times}10^{-8}\;A/cm^{2}$ at the reverse bias of -10 V.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 추계학술발표강연 및 논문개요집
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• pp.20-20
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• 2003

We developed 30 ㎽-AlInGaN based violet laser diodes. The fabrication procedures of the laser diodes are described as follows. Firstly, GaN layers having very low defect density were grown on sapphire substrates by lateral epitaxial overgrowth method. The typical dislocation density was about 1-3$\times$10$^{6}$ /$\textrm{cm}^2$ at the wing region. Secondly, AlInGaN laser structures were grown on LEO-GaN/sapphire substrates by MOCVD. UV activation method, instead of conventional annealing, was conducted to achieve good p-type conduction. Thirdly, ridge stripe laser structures were fabricated. The cavity mirrors were formed by cleaving method. Three pairs of SiO$_2$ and TiO$_2$ layers were deposited on the rear facet for mirror coating. Lastly, laser diode chips were mounted on AlN submount wafers by epi-down bonding method. The lifetime of the laser diodes was over 10,000 hrs at room temperature under automatic power controlled condition. We expect the performance of the LDs to be improved by the optimization of the growth and fabrication process. The detailed characteristics and important issues of the laser diodes will be discussed at the conference.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 추계학술대회 논문집
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• pp.193-194
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• 2009

This report makes an important correction to estimating angular dependent emission pattern of Organic Light-Emitting Diodes (OLEDs). Today, experiments on measuring angular light intensity of OLEDs are conducted without considering the difference between the view angle identified by photodiode and the actual angle being measured. ITO-TPD-$Alq_3$-LiF-Al Organic Light-Emitting Diode was used to find out the degree of the error. In this case, the difference in average was about $1^*$, which is highly significant. Since the difference varies from case to case, the need for adjustment must be evaluated for each case.

• ETRI Journal
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• 제32권2호
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• pp.312-318
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• 2010

A small reconfigurable patch antenna is proposed to achieve polarization diversity for digital multimedia broadcasting systems at 2.6 GHz. To obtain polarization diversity, a pair of on-slit PIN diodes is inserted in each diagonal of a cross-shaped patch. Thus, four PIN-diodes on these slits are utilized to change the connection of the slits and thus achieve polarization. Bias circuits for the diodes are allocated in the cutting corner of the cross-shaped patch to minimize the antenna size. The antenna produces left-hand circular polarization, right-hand circular polarization, or linear polarization, depending on the PIN-diode status. Analysis of circular polarization operation is explicated. Measurements show a gain of about 1.5 dB, a cross polarization of about -20 dB, and an axial ratio of about 2.5 dB.