• Progress in Medical Physics
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• v.17 no.1
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• pp.17-23
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• 2006

In Vivo dosimetry is a method to evaluate the radiotherapy; it is used to find the dosimetric and mechanical errors of radiotherapy unit. In this study, on-line In Vivo dosimetry was enabled by measuring the skin dose with MOSFET detectors attached to patient's skin during treatment. MOSFET dosimeters were found to be reproducible and independent on beam directions. MOSFET detectors were positioned on patient's skin underneath of the dose build-up material which was used to minimize dosimetric error. Delivered dose calculated by the plan verification function embedded in the radiotherapy treatment planning system (RTPs), was compared with measured data point by point. The dependency of MOSFET detector used in this study for energy and dose rate agrees with the specification provided by manufacturer within 2% error. Comparing the measured and the calculated point doses of each patient, discrepancy was within 5%. It was enabled to verify the IMRT by using MOSFET detector. However, skin dosimetry using conventional ion chamber and diode detector is limited to the simple radiotherapy.

• Proceedings of the KIPE Conference
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• 2018.11a
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• pp.92-94
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• 2018

본 논문은 SiC MOSFET 디바이스를 사용하는 전력변환장치에서 Rogowski 코일을 이용하여 SiC MOSFET 디바이스에 흐르는 전류를 측정하여, 과전류를 검출하고 게이팅 신호를 차단하는 기법에 관하여 연구한다. SiC MOSFET는 소자의 특성으로 보편적으로 사용되는 과전류 검출 방법인 DeSAT 적용이 어렵기 때문에 Rogowski 코일을 사용하여 스위치 전류를 측정, 과전류를 검출한다. 본 논문에서는 PCB패턴 Rogowski 코일의 설계 방법뿐만 아니라 Rogowski 코일과 적분기의 대역폭에 대해서도 논의한다. 실험은 직류링크 커패시터에 SiC MOSFET 스위치 레그를 병렬로 연결하고, 직류링크 커패시터에 직류전압을 충전 후 스위치 레그를 약 6us정도 단락시켜 SiC MOSFET에 과전류를 발생시킨다. 이 때, 제안한 Rogowski 코일을 이용한 과전류 검출 및 차단 기법의 적용 전후를 비교하여 동작 및 성능(검출 및 차단 소요시간)을 확인한다. 마지막으로 실험 결과를 통해 본 논문에서 제안한 PCB패턴 Rogowski 코일을 이용하여 과전류 검출 및 차단 기법이 검증되었다.

• Journal of Radiation Protection and Research
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• v.31 no.4
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• pp.165-171
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• 2006

In Korea, a real-time effective dose measurement system is in development. The system uses 32 high-sensitivity MOSFET dosimeters to measure radiation doses at various organ locations in an anthropomorphic physical phantom. The MOSFET dosimeters are, however, mainly made of silicon and shows some degree of energy and angular dependence especially for low energy photons. This study determines the correction factors to correct for these dependences of the MOSFET dosimeters for accurate measurement of radiation doses at organ locations in the phantom. For this, first, the dose correction factors of MOSFET dosimeters were determined for the energy spectrum in the steam generator channel of the Kori Nuclear Power Plant Unit #1 by Monte Carlo simulations. Then, the results were compared with the dose correction factors from 0.652 MeV and 1.25 MeV mono-energetic photons. The difference of the dose correction factors were found very negligible $(\leq1.5%)$, which in general shows that the dose corrections factors determined from 0.662 MeV and 1.25 MeV can be in a steam general channel head of a nuclear power plant. The measured effective dose was generally found to decrease bit $\sim7%$ when we apply the dose correction factors.

• Progress in Medical Physics
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• v.15 no.4
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• pp.215-219
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• 2004

Due to their excellence for the high-energy therapy range of photon beams, researchers show increasing interest in applying MOSFET dosimeters to low- and medium-energy applications. In this energy range, however, MOSFET dosimeter is complicated by the fact that the interaction probability of photons shows significant dependence on the atomic number, Z, due to photoelectric effect. The objective of this study is to develop a very detailed 3-dimensional Monte Carlo simulation model of a MOSFET dosimeter for radiological characterizations and calibrations. The sensitive volume of the High-Sensitivity MOSFET dosimeter is very thin (1 ${\mu}{\textrm}{m}$) and the standard MCNP tallies do not accurately determine absorbed dose to the sensitive volume. Therefore, we need to score the energy deposition directly from electrons. The developed model was then used to study various radiological characteristics of the MOSFET dosimeter. the energy dependence was quantified for the energy range 15 keV to 6 MeV; finding maximum dependence of 6.6 at about 40 keV. A commercial computer code, Sabrina, was used to read the particle track information from an MCNP simulation and count the tracks of simulated electrons. The MOSFET dosimeter estimated the calibration factor by 1.16 when the dosimeter was at 15 cm depth in tissue phantom for 662 keV incident photons. Our results showed that the MOSFET dosimeter estimated by 1.11 for 1.25 MeV photons for the same condition.

• Proceedings of the IEEK Conference
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• 2009.05a
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• pp.159-162
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• 2009

The necessity of radiation dosimeter with precise measurement of radiation dose is increased and required in the field of spacecraft, radiotheraphy hospital, atomic plant facility, etc. where radiation exists. Until now, a low power commercial metal-oxide semiconductor(MOS) transistor has been tested as a gamma radiation dosimeter. The measurement error between the actual value and the measurement one can occur since the MOSFET(MOS field-effect transistor) dosimeter, which is now being used, has two gates with same width. The measurement value of dosimeter depends on the variation of threshold voltage, which can be affected by the environment such as temperature. In this paper, a radiation dosimeter having a pair of MOSFET is designed in the same silicon substrate, in which each of the MOSFETs is operable in a bias mode and a test mode. It can measure the radiation dose by the difference between the threshold voltages regardless of the variation of temperature.

• Journal of the Institute of Convergence Signal Processing
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• v.11 no.2
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• pp.163-168
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• 2010

This paper presents the practical implementation of an over-temperature protection system for power semiconductor devices. In the proposed system, temperature variation is provided with just using $R_{ds(on)}$ characteristics of power MOSFET, while extra device such as a temperature sensor or an over-temperature detection transistor is needed to monitor the temperature in the conventional method. The proposed protection technique is experimentally tested on IRF840 power MOSFET. The PIC microcontroller PIC16F877A is used for the implementation of the proposed protection algorithm. The built-in 10-bit A/D converter is utilized for detecting voltage variance between a drain and a source of IRF840. The induced temperature-resistance relationship based on the measured drain-source voltage, supplies a gate signal to the power MOSFET. If detected temperature's voltage exceeds any a protection temperature's voltage, the microcontroller removes the trigger signal from the power MOSFET. These test results showed satisfactory performances of the proposed protection system in term of accuracy within 1.5%.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.2
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• pp.71-80
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• 1999

In this paper, a power MOSFET driver with protection circuits is designed using a 2${\mu}m$ high-voltage CMOS process. For stable operations of control circuits a power managing circuit is designed, and a voltage-detecting short-circuit protection(VDSCP) is proposed to protect a voltage regulator in the power control circuit. The proposed VDSCP scheme eliminates voltage drop caused by a series resistor, and turns off output current under short-circuit state. To protect a power MOSFET, a short-load protection, a gate-voltage limiter, and an over-voltage protection circuit are also designed A high voltage 2 ${\mu}m$ technology provides the breakdown voltage of 50 V. The driver consumes the power of 20 ~ 100 mW along its operation state excluding the power of the power MOSFET. The active area of the power MOSFET driver occupies $3.5 {\times}2..8mm^2$.

• Journal of IKEEE
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• v.22 no.2
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• pp.393-401
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• 2018

In this paper, a rectifier for WPC / A4WP wireless power transmission is designed. The proposed rectifier supports both WPC (Wireless Power Consortium) and A4WP (Alliance For Wireless Power) and is designed with full-bridge rectifier. WPC transmits power at the frequency of 100kHz to 205kHz and A4WP at the frequency of 6.75MHz. Since the bridge rectifier uses a MOSFET instead of a diode, the reverse current flows and the efficiency is affected if the output voltage is higher than the input voltage. Therefore, we added the reverse current detector that detects the current flowing through the MOSFET and shut off the reverse current. The frequency discriminator is used because the rectifier has different frequency band. The proposed rectifier was designed using $0.35{\mu}m$ CMOS high voltage process. The input voltage is up to 18V and the rectifier operates at 100kH to 205kHz, 6.78MHz frequency. The maximum efficiency is 94.8% and the maximum power transfer is 5.78W.

• Journal of Radiation Protection and Research
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• v.31 no.2
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• pp.97-104
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• 2006

In recent years, the MOSFET dosimeter has been widely used in various medical applications such as dose verification in radiation therapeutic and diagnostic applications. The MOSFET dosimeter is, however, mainly made of silicon and shows some energy dependence for low energy Photons. Therefore, the MOSFET dosimeter tends to overestimate the dose for low energy scattered photons in a phantom. This study determines the correction factors to compensate these dependences of the MOSFET dosimeter in ATOM phantom. For this, we first constructed a computational model of the ATOM phantom based on the 3D CT image data of the phantom. The voxel phantom was then implemented in a Monte Carlo simulation code and used to calculate the energy spectrum of the photon field at each of the MOSFET dosimeter locations in the phantom. Finally, the correction factors were calculated based on the energy spectrum of the photon field at the dosimeter locations and the pre-determined energy and directional dependence of the MOSFET dosimeter. Our result for $^{60}Co$ and $^{137}Cs$ photon fields shows that the correction factors are distributed within the range of 0.89 and 0.97 considering all the MOSFET dosimeter locations in the phantom.

• Journal of Sensor Science and Technology
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• v.15 no.1
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• pp.1-6
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• 2006

We fabricated Si nano-wire MOSFET by using the conventional photolithography with a $1.5{\mu}m$ resolution. Si nano-wire was fabricated by using reactive ion etching (RIE), anisotropic wet etching and thermal oxidation on a silicon-on-insulator (SOI) substrate, and its width is 30 nm. Logarithmic circuit consisting of a NMOSFET and Si nano-wire MOSFET has been constructed for application to high-sensitivity image sensor. Its sensitivity was 1.12 mV/lux. The output voltage swing was 1.386 V.