• Proceedings of the KIPE Conference
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• 2000.07a
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• pp.376-379
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• 2000

This paper presents an improved ZVS partial series resonant DC/DC converter (PSRC) with low conduction losses suitable for high power and high frequency applications. The proposed PSRC have advantages of zero-voltage-swiching (ZVS) of main switches for entire load ranges and low conduction losses of main switches by decreasing current stresses Also the reduction of the effective duty cycle is not occurred during the resonant period of the main circuit because the auxiliary circuit of the proposed converter is placed out of the main power path. An improved ZVS PSRC has a so much characteristics with respect to the reduction of current stress. The operation principles of the proposed converter are explained in detail and the various simulated and experimental results show the validity of the proposed converter.

• Journal of the Korean Ceramic Society
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• v.55 no.5
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• pp.440-445
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• 2018

To control the electrical properties of a SiC heating element, we sintered $SiC-ZrB_2$composites by using the spark plasma sintering method. The addition of $ZrB_2$ particles with lower electrical conductivity to the SiC matrices with comparatively higher electrical resistivity lowers the electrical resistivities of the composite material. The $ZrB_2$ particles aggregate to form large particles and 3-1, 3-2, and 3-3 networks, i.e., conduction paths. In our study, about $1-{\mu}m$-sized $ZrB_2$ powders start to form the conduction path at about 10 vol.% of addition, namely the threshold volume. The Joule heating experiment shows that 20 vol.% $ZrB_2$-added SiC heating element has outstanding heating efficiency.

• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.195-196
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• 2012

In recent years, in an effort to improve the efficiency and the power density of the front-end power factor correction(PFC), the interleaving of multiple converter is employed. The conventional interleaved continuous conduction mode(CCM) boost PFC converter requires input and output voltage sensing and three current sensing to obtain current balancing between modules. In this paper, the interleaved CCM PFC converter based on modulated carrier control is proposed. With the proposed method, two phase interleaved PFC can be realized simply without line voltage sensing resistor and can achieve current balancing without additional current sensing resistor on common return path. The simulation studies are carried out to verify the effectiveness of the proposed control scheme.

• Computers and Concrete
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• v.12 no.3
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• pp.261-283
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• 2013

This paper aims to contribute to the three-dimensional generalization of numerical prediction of crack propagation through the formulation of finite elements with embedded discontinuities. The analysis of crack propagation in two-dimensional problems yields lines of discontinuity that can be tracked in a relatively simple way through the sequential construction of straight line segments oriented according to the direction of failure within each finite element in the solid. In three-dimensional analysis, the construction of the discontinuity path is more complex because it requires the creation of plane surfaces within each element, which must be continuous between the elements. In the method proposed by Chaves (2003) the crack is determined by solving a problem analogous to the heat conduction problem, established from local failure orientations, based on the stress state of the mechanical problem. To minimize the computational effort, in this paper a new strategy is proposed whereby the analysis for tracking the discontinuity path is restricted to the domain formed by some elements near the crack surface that develops along the loading process. The proposed methodology is validated by performing three-dimensional analyses of basic problems of experimental fractures and comparing their results with those reported in the literature.

• Proceedings of the Korean Magnestics Society Conference
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• 2000.09a
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• pp.325-326
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• 2000

Low temperature diagnosis was performed as a probe for the integrity of MTJ(Magnetic tunnel junction) process which is optimised for the given plasma oxidation condition. TMR ratio increased slowly with decreasing temperature than that expected from spin wave exitation theory〔1〕. Junction resistance (RJ) does not follow T$\^$-$\frac{1}{2}$/ law below 200 K, indicating another conduction path besides spin polarized tunneling is involved at low temperature. Temperature dependence of conductance dip and bias dependence of TMR with temperature are discussed, from which the quality of tunnel barrier and its formation process can be inferred.

• Proceedings of the KIPE Conference
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• 2008.06a
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• pp.544-546
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• 2008

An improved dual-path energy recovery circuit (ERC) using a current source and a voltage source for plasma display panel (PDP) is proposed. The proposed ERC uses the voltage source to charge a panel and the current source to discharge the panel. Thus, the proposed circuit can make the panel charge to $V_S$ and discharge to 0V, fully and it is possible to achieve zero voltage switching (ZVS) of all switches in H-bridge inverter and zero current switching (ZCS) of all switches in the ERC. Moreover, it has less conduction and switching loss in ERC devices by the dual energy recovery paths for charging and discharging the panel. Furthermore, it has features of canceling the gas discharge current, high performance and the low cost ERC components. The operation principle and features of the proposed ERC are presented in detail and verified with 42-inch SD PDP.

• Journal of Power Electronics
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• v.16 no.3
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• pp.905-914
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• 2016

A high-performance rectifier is introduced in this study. The proposed rectifier combines the conventional pulse width modulation, soft commutation, and instantaneously average line current control techniques to promote circuit performance. The voltage stresses of the main switches in the rectifier are lower than those in conventional rectifier topologies. Moreover, conduction losses of switches in the rectifier are certainly lower than those in conventional rectifier topologies because the power current flow path when the main switches are turned on includes two main power semiconductors and the power current flow path when the main switches are turned off includes one main power semiconductor. The rectifier also adopts a ZCS-PWM auxiliary circuit to derive the ZCS function for power semiconductors. Thus, the problem of switching losses and EMI can be improved. In the control strategy, the controller uses the average current control mode to achieve fixed-frequency current control with stability and low distortion. A prototype has been implemented in the laboratory to verify circuit theory.

• Journal of Power Electronics
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• v.19 no.4
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• pp.1011-1019
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• 2019

In this paper, a buck-flyback (fly-buck) stand-alone photovoltaic (PV) system for charge balancing with a differential power processor (DPP) circuit is proposed. Conventional feed-back DPP converters draw differential feed-back power from the output of a string converter. Therefore, the power is always through the switches and diodes of the string converter. Because of the returning conduction path, there are always power losses due to the resistance of the switch and the forward voltage of the diode. Meanwhile, the proposed feed-back DPP converter draws power from the magnetically-coupled inductor in a string converter. This shortens the power path of the DPP converter, which reduces the power losses. In addition, the extra winding in the magnetically-coupled inductor works as a charge balancer for battery-stacked stand-alone PV systems. The proposed system, which uses a single magnetically-coupled inductor, can control each of the PV modules independently to track the maximum power point. Thus, it can overcome the power loss due to the power path. It can also achieve charge balancing for each of the battery modules. The proposed topology is analyzed and verified using 120W hardware experiments.

• Journal of the Semiconductor & Display Technology
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• v.15 no.4
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• pp.10-15
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• 2016

In this paper, novel ball grid array (BGA) interconnection process using solderable anisotropic conductive adhesives (SACAs) with low-melting-point alloy (LMPA) fillers have been developed to enhance the processability in the conventional capillary underfill technique and to overcome the limitations in the no-flow underfill technique. To confirm the feasibility of the proposed technique, BGA interconnection test was performed using two types of SACA with different LMPA concentration (0 and 4 vol%). After the interconnection process, the interconnection characteristics such as morphology of conduction path and electrical properties of BGA assemblies were inspected and compared. The results indicated that BGA assemblies using SACA without LMPA fillers showed weak conduction path formation such as solder bump loss or short circuit formation because of the expansion of air bubbles within the interconnection area due to the relatively high reflow peak temperature. Meanwhile, assemblies using SACA with 4 vol% LMPAs showed stable metallurgical interconnection formation and electrical resistance due to the favorable selective wetting behavior of molten LMPAs for the solder bump and Cu metallization.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.239.1-239.1
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• 2011

Dye sensitized solar cells (DSC) are promising devices for inexpensive, nontoxic, transparent, and large-scale solar energy conversion. Generally thick $TiO_2$ nanoporous films act as efficient photoanodes with their large surface area for absorbing light. However, electron transport through nanoparticle networks causes the slowdown and the loss of electron transport because of a number of interparticle boundaries inside the conduction path. We have studied DSCs with precisely dimension-controlled $TiO_2$ nanotubes array as photoanode. $TiO_2$ nanotubes array is prepared by template-directed fabrication method with atomic layer deposition. Well-ordered nanotubes array provides not only large surface area for light absorbing but also direct pathway for electrons with minimalized grain boundaries. Large enlongated anatase grains in the nanotubes could enhance the conductivity of electrons, but also suppress the recombination with holes through defect sites during diffusion into the electrode. To study the effect of grain boundaries, we fabricated two kinds of nanotubes which have different grain sizes by controlling deposition conditions. And we studied electron conduction through two kinds of nanotubes with different grain structures. The solar cell performance was studied as a function of thickness and grain structures. And overall solar-to-electric energy conversion efficiencies of up to 7% were obtained.