• JSTS:Journal of Semiconductor Technology and Science
• /
• v.16 no.2
• /
• pp.221-225
• /
• 2016

This paper reports a new method to enable the normally-off operation of AlGaN/GaN heterojunction field-effect transistors (HFETs). A capacitor was connected to the gate input node of a normally-on AlGaN/GaN HFET with a Schottky gate where the Schottky gate acted as a clamping diode. The combination of the capacitor and Schottky gate functioned as a clamp circuit to downshift the input signal to enable the normally-off operation. The normally-off operation with a virtual threshold voltage of 5.3 V was successfully demonstrated with excellent dynamic switching characteristics.

• Korean Chemical Engineering Research
• /
• v.60 no.2
• /
• pp.313-319
• /
• 2022

AlGaN/GaN based HfO₂ MOSHEMT (metal oxide semiconductor high electron transistor) with different gate recess depth was simulate to demonstrate a successful normally-off operation of the transistor. Three types of the HEMT structures including a conventional HEMT, a gate-recessed HEMT with 3 nm thick AlGaN layer, and MIS-HEMT without AlGaN layer in the gate region. The conventional HEMT showed a normally-on characteristics with a drain current of 0.35 A at V_G = 0 V and V_DS = 15 V. The recessed HEMT with 3 nm AlGaN layer exhibited a decreased drain current of 0.15 A under the same bias condition due to the decrease of electron concentration in 2DEG (2-dimensional electron gas) channel. For the last HEMT structure, distinctive normally- off behavior of the transistor was observed, and the turn-on voltage was shifted to 0 V.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.25 no.3
• /
• pp.137-142
• /
• 2013

A small air-conditioner or chiller for a constant temperature bath normally uses a constant speed compressor. The constant speed compressor is relatively inexpensive, but it uses on/off control for capacity modulation. The on/off control has several disadvantages, specifically energy loss and large temperature fluctuation. Continuous operation with a bypass system can be an alternative to on/off control, for capacity modulation. In this study, a heat pump system having a hot-gas bypass and a liquid bypass was adopted. The performance of the bypass-type heat pump was measured, by varying the bypass valve opening. The differences of the COP between the hot-gas bypass and the liquid bypass, in the cooling and heating operations, were within 2% and 1%, respectively. The liquid bypass showed a wider range of capacity control in the cooling operation but the hot-gas bypass showed a wider range of capacity control in the heating operation.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.33 no.1
• /
• pp.16-20
• /
• 2020

In this study, a patterning method using self-aligned nanostructures was introduced to fabricate GaN-based fin-gate HEMTs with normally-off operation, as opposed to high-cost, low-productivity e-beam lithography. The honeycomb-shaped fin-gate channel width is approximately 40~50 nm, which is manufactured with a fine width using a proposed method to obtain sufficient fringing field effect. As a result, the threshold voltage of the fabricated device is 0.6 V, and the maximum normalized drain current and transconductance of Gm are 136.4 mA/mm and 99.4 mS/mm, respectively. The fabricated devices exhibit a smaller sub-threshold swing and higher Gm peak compared to conventional planar devices, due to the fin structure of the honeycomb channel.

• ETRI Journal
• /
• v.39 no.1
• /
• pp.62-68
• /
• 2017

In this paper, we present the design and characterization analysis of a cascode GaN field-effect transistor (FET) for switching power conversion systems. To enable normally-off operation, a cascode GaN FET employs a low breakdown voltage (BV) enhancement-mode Si metal-oxide-semiconductor FET and a high-BV depletion-mode (D-mode) GaN FET. This paper demonstrates a normally-on D-mode GaN FET with high power density and high switching frequency, and presents a theoretical analysis of a hybrid cascode GaN FET design. A TO-254 packaged FET provides a drain current of 6.04 A at a drain voltage of 2 V, a BV of 520 V at a drain leakage current of $250{\mu}A$, and an on-resistance of $331m{\Omega}$. Finally, a boost converter is used to evaluate the performance of the cascode GaN FET in power conversion applications.

• Proceedings of the KSR Conference
• /
• 2004.10a
• /
• pp.756-762
• /
• 2004

Up to now, the only way is Floating Slab Track System, which cuts off vibration by installing spring between concrete slab and ground for the lines of particularly requiring attenuating vibration. The weak point of Floating Slab Track System is large increase of construction cost because normally the structure is getting bigger. In regards to this matter, Floating Rail Track System has been developed, which cuts off vibration by floating the first cause of vibration rail, and the system is in operation. In the thesis, the application of new attenuating vibration track system has been confirmed by studying theoretical background of Floating Rail Track System and evaluating dynamic deflection of track and attenuating of noise and vibration performance through various measurements from laboratory tests and site inspection.

• Journal of Biosystems Engineering
• /
• v.32 no.5
• /
• pp.284-291
• /
• 2007

This study was to investigate performance of position, basic controls and additional control for man-machine interface on a 3-point hitch of a tractor. The developed additional control was one-touchup, backup, turnup, liftarm limited, PTO on/off and an external control. As a result of experiment, maximum steady state error of response system was lower than $0.8^{\circ}$ and this result showed the function operated normally because the dead band of system set was ${\pm}1^{\circ}$. There was no abnormal situation by switch operation and sensor signal during the performance test. The results of experiment showed the characteristics of the response was sufficient to be used as the position and additional control system for tractors.

• Journal of Ocean Engineering and Technology
• /
• v.19 no.4 s.65
• /
• pp.21-27
• /
• 2005

Large welded structures, including ships and offshore structures, are normally in operation under cyclic fatigue loadings. These structures include many geometric discontinuities, as well as material discontinuities due to weld joints. The fatigue strength at these hot spots is very important for the structural performance. In the past, various Non Destructive Evaluation (NDE) techniques have been developed to detect fatigue cracks and to estimate their location and size. However, an important limitation of most of the existing NDE methods is that they are off line; the normal operation of the structure has to be interrupted, and the device often has to be disassembled. This study explores the development of a structural health monitoring system, with a special interest in applying the technique to welded structural members in ship and offshore structures. In particular, the impedance based structural health monitoring technique that employs the coupling effect of piezoceramic (PZT) materials and structures is investigated.

• Special Issue of the Society of Naval Architects of Korea
• /
• 2007.09a
• /
• pp.89-93
• /
• 2007

The Boil-off gas (BOG) generation during the voyage is inevitable since Natural Gas (NG) in normally liquefied below -160 degree C in atmosphere condition and small heat ingress due to relatively hot outside keeps evaporating continuously. The one of major issue in LNG carriers is to handle generated BOG from cargo tank. The generated BOG affects to increase the cargo tank pressure and Gas Management System (GMS) for LNG carriers is closely related to cargo tank pressure maintenance. Economically, BOG is generally used as fuel in LNG carrier. Newly developed GMS for LNG carrier in boiler propulsion system, VaCo System, not only accomplish automatic control in GMS but also ensure safer operation.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.18 no.1
• /
• pp.167-171
• /
• 2018

We have developed ideal products that need low power by utilizing astable multivibraters since we are in need of technology that can be adaptable to any environments anytime because tons of thousands of electric products and IT products need to be operated by low power DC motors. Since motors generally use much electricity in an initial stage of operation, we have testified and proved the technology that can be furnished with any kinds of motors including those of AC and DC by loading them with on-off systems with electric pulse with operating methodology that has realized low-electrical operation when normally operated.