• Proceedings of the KIPE Conference
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• 2000.07a
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• pp.1-5
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• 2000

This paper deals with the modeling and analysis of the high voltage flyback transformer (HVFBT) often utilized in small-sized high voltage DC power supplies. The parasitic capacitance of th HVFBT with the large turns of the secondary winding causes the undesirable parasitic resonance in the transient state which produces the high current stress and limits the switching frequency of the converter. In order to analyze this phenomenon the equivalent circuit model including the parasitic capacitance is derived and the frequency characteristics are provided. The parasitic resonance in the switching states is also investigated based on this equivalent circuit model. The derived model and analysis is finally validated through the SPICE simulation and experiments.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.66 no.4
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• pp.213-218
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• 2017

The DC electrolytic capacitor for DC-link of power converter is widely used in various power electronic circuits and system application. Its functions include, DC Bus voltage stabilization, conduction of ripple current due to switching events, voltage smoothing, etc. Unfortunately, DC electrolytic capacitors are some of the weakest components in power electronics converters. Many papers have proposed different algorithms or diagnosis method to determinate the ESR and tan ${\delta}$ capacitance C for fault alarm system of the electrolytic capacitor. However, both ESR vary with frequency and temperature. Accurate knowledge of both parameters at the capacitors operating conditions is essential to achieve the best reference data of fault alarm. According to parameter analysis, the capacitance increases with temperature and the initial ESR decreases. Higher frequencies make the reference ESR with the initial ESRo value to decrease. Analysis results show that the proposed DC Bus electrolytic capacitor reference ESR model setting technique can be applied to advanced reference signal of capacitor diagnosis systems successfully.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.6
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• pp.558-565
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• 2015

Gallium nitride high-electron mobility transistor (GaN HEMT) is the strongest candidate for replacing Si MOSFET. Comparing the figure of merit (FOM) of GaN with the state-of-the-art super junction Si MOSFET, the FOM is much better because of the wide band gap characteristics and the heterojunction structure. Although GaN HEMT has many benefits for the power conversion system, the performance of the power conversion system with the GaN HEMT is sensitive because of its low threshold voltage ($V_{th}$) and even lower parasitic capacitance. This study examines the characteristics of a phase-shifted full-bridge dc-dc converter with cascode GaN HEMT. The problem of unoptimized dead time is analyzed on the basis of the output capacitance of GaN HEMT. In addition, the printed circuit board (PCB) layout consideration is analyzed to reduce the negative effects of parasitic inductance. A comparison of the experimental results is provided to validate the dead time and PCB layout analysis for a phase-shifted full-bridge dc-dc converter with cascode GaN HEMT.

• Journal of IKEEE
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• v.23 no.1
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• pp.261-265
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• 2019

We analyze the failure rate change of a conventional bidirectional converter and a modified one which moves an output capacitor towards propulsion battery. We analysis of the circuit structural homogeneity and the difference between both converters, and confirm that the capacitor working voltage is reduced by changing the capacitor position. After obtaining the capacitor failure rate according to voltage stress factor and operating temperature, it is applied to the fault-tree of the bidirectional converter to obtain the overall failure rate of the converter. We analyzes the advantages and disadvantages of design changes by comparing and analyzing the failure rate and mean time between failures (MTBF) according to operating temperature and capacitance value.

• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.5
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• pp.504-510
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• 2015

This paper presents a power and area efficient SAR ADC for multi-channel near threshold-voltage (NTV) applications such as neural recording systems. This work proposes a split dual-capacitive-array (S-DCA) structure with shifted input range for ultra low-switching energy and architecture of multi-channel single-ended SAR ADC which employs only one comparator. In addition, the proposed ADC has the same amount of equivalent capacitance at two comparator inputs, which minimizes the kickback noise. Compared with conventional SAR ADC, this work reduces the total capacitance and switching energy by 84.8% and 91.3%, respectively.

• Journal of Power Electronics
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• v.12 no.1
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• pp.113-119
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• 2012

This paper describes the design and control of a phase shift full bridge converter with a current doubler, which can be used for the on-board charger for the lead-acid battery of electric forklifts. Unlike the common resistance load, the battery has a large capacitance element and it absorbs the entire converter output ripple current, thereby shortening the battery life and degrading the system efficiency. In this paper a phase shift full bridge converter with a current doubler has been adopted to decrease the output ripple current and the transformer rating of the charger. The charge controller is designed by using the small signal model of the converter, taking into consideration the internal impedance of the battery. The stability and performance of the battery charger is then verified by constant current (CC) and constant voltage (CV) charge experiments using a lead-acid battery bank for an electric forklift.

• Journal of Power Electronics
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• v.9 no.3
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• pp.430-437
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• 2009

This paper presents the dynamic characteristics of buck and buck-boost dc-dc converters with digital filters. At first, the PID, the minimum phase FIR filter and the IIR filter controls are discussed in the buck dc-dc converter. Comparisons of the dynamic characteristics between the buck and buck-boost converters are then discussed. As a result, it is clarified that the superior dynamic characteristics are realized in the IIR filter method. In the buck converter, the undershoot is less than 2% and the transient time is less than 0.4ms. On the other hand, in the buck-boost converter, the undershoot is about 3%. However, the transient time is approximately over 4ms because the output capacitance is too large to suppress the output voltage ripple in this type of converter.

• The Journal of the Acoustical Society of Korea
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• v.37 no.1
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• pp.46-52
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• 2018

The piezoelectric single crystals used in piezoelectric transformers have a problem that power transfer capacity is comparatively low due to their high input impedance. In this study, we suggest a method to improve the power transfer capacity by reducing the high input impedance of the piezoelectric single crystal vibrator by connecting a capacitance increasing circuit to the electrical terminals of the piezoelectric single crystal vibrator where the circuit is a GIC (Generalized Impedance Converter) circuit using operational amplifiers. The result of measuring driving characteristics after applying the designed capacitance increasing circuit to the $128^{\circ}$ rotated Y-cut $LiNbO_3$ crystal vibrator confirmed that the input impedance decreased by 25 %, electromechanical coupling factor increased by 30 %, and the power transfer capacity increased by about 17 to 30 times in voltage conversion characteristics.

• Journal of the Semiconductor & Display Technology
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• v.21 no.2
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• pp.107-111
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• 2022

In this paper, a plastic film type submersion sensor capable of measuring submersion speed was developed. This submersion sensor is designed as a capacitive type, and it is a sensor that outputs the change in capacitance between the electrode of the submersion sensor and the grounded body as a voltage through a C-V(capacitance-voltage) converter. We developed an submersion sensor in which two electrodes of different lengths are connected in parallel to measure the submersion speed accurately by minimizing the influence of noise such as contamination. When both electrodes of the submersion sensor are exposed to water, the rate of change of water level suddenly increases, so the submersion speed is measured by measuring the time to this point. Since the difference in length between the two electrodes of the submersion sensor does not change in any case, it is possible to accurately measure the submersion speed.

• Journal of IKEEE
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• v.19 no.1
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• pp.110-117
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• 2015

In this paper, a novel trench power MOSFET using a Separate-W-gated technique MOSFET (SWFET) is proposed. Because the SWFET has a very low $Q_{GD}$ compared to other forms of technology, it can be applied to high-speed power systems. The results found that the SWFET-applied $Q_{GD}$ was decreased by 40% when compared to simply using the more conventional trench gate MOSFET. $C_{ISS}$ (input capacitance : $C_{GS}+C_{GD}$), $C_{OSS}$ (output capacitance : $C_{GD}+C_{DS}$) and $C_{RSS}$ (reverse recovery capacitance : $C_{GD}$) were improved by 24%, 40%, and 50%, respectively. The switching characteristics of the inverter circuit shows a 24.9% enhancement of reverse recovery time, and the power efficiency of the DC-DC buck converter increased by 14.2%. In addition, the proposed SWFET does not require additional process steps and There was no degradation in the electrical performance of the current-voltage and on-resistance.