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Younghun Ko,Hong-Soo Cho,Sang-Sung Lee,So-Bong Shin,Yongchul Song,Sang-Gug Lee Institute of Electrical and Electronics Engineers 2016 IEEE transactions on power electronics Vol. No.
<P>In this paper, a flicker-free transformer-less multi-channel light-emitting diode (LED) driver that adopts a new power factor enhancement technique is presented. The proposed LED driver divides the transmission path of the current to the LED string in two ways depending on the instantaneous input voltage in order to improve the PF relative to that of a conventional compact flicker-free LED driver that uses a fixed LED current regulation scheme with only one electrolytic capacitor. The proposed driver can be implemented with a minimum number of external components leading to a compact module that allows a light bulb with omnidirectional light emission. In order to enhance the expandability of the smart bulb, a conventional buck converter with 3-V output is integrated with the proposed LED driver to supply the peripherals of the module. The proposed LED driver IC is implemented in a 0.35-mu m ultrahigh voltage CMOS process and occupies an area of 2.9 mm x 2.0 mm. A 10-W smart bulb prototype that adopts the proposed LED driver is flicker free and shows a power factor of 0.715 and power conversion efficiency of 77.5% for an ac supply of 120 V.</P>
심해저용 전기 저항 용접 소구경 송유관 소재의 온도 및 변형률 속도 에 따른 유동 응력 특성
김영훈(Younghun Kim),박성주(Sung-Ju Park),윤성원(Sung-Won Yoon),정준모(Joonmo Choung) 한국해양공학회 2015 韓國海洋工學會誌 Vol.29 No.3
A subsea pipeline for oil/gas transportation or gas injection is subjected to extreme variation in internal pressure and temperature, which can involve a strain rate on the pipeline material. This paper describes the flow stress characteristics of a pipeline material called API 5L X52N PSL2, using and experimental approach. High-speed tensile tests were carried out for two metal samples taken from the base and weld parts. The target temperature was 100℃, but two other temperature levels of ?20℃ and 0℃ were taken into account. Three strain rates were also considered for each temperature level: quasi static. 1/s, and 10/s. Flow stress data were proposed for each temperature level according to these strain rates. The dynamic hardening behaviors of the base and weld metals appeared to be nonlinear on the log-scale strain rate axis. A very high material constant value was required for the Cowper-Symonds constitutive equation to support the experimental results.
Sung, Hwa Kyung,Oh, Seung Yeon,Park, Chulhwan,Kim, Younghun American Chemical Society 2013 Langmuir Vol.29 No.28
<P>A highly sensitive colorimetric sensing platform for the selective trace analysis for Co<SUP>2+</SUP> ions is reported, based on glutathione (GSH)-modified silver nanoparticles (AgNP). The shape of metallic nanoparticles used in colorimetric detection, using the unique optical properties of plasmonic nanoparticles, is almost spherical. Therefore, in this work we attempted to investigate the selective detection of heavy metal ion (Co<SUP>2+</SUP>), with the shape of AgNPs (nanosphere, nanoplate, and nanorod). GSH-AgNP with spherical shape shows a high sensitivity for all of the metal ions (Ni<SUP>2+</SUP>, Co<SUP>2+</SUP>, Cd<SUP>2+</SUP>, Pb<SUP>2+</SUP>, and As<SUP>3+</SUP>) but poor selective recognition for target metal ions. Whereas, AgNPs solution containing rod-type GSH-AgNP has a special response to Co<SUP>2+</SUP>, and its selective detection might be based on the cooperative effect of CTAB and GSH. Therefore, Co<SUP>2+</SUP> ion could be selectively recognized using rod-type GSH-AgNPs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2013/langd5.2013.29.issue-28/la401408f/production/images/medium/la-2013-01408f_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la401408f'>ACS Electronic Supporting Info</A></P>
A Fast Low Dropout Regulator with High Slew Rate and Large Unity-Gain Bandwidth
Younghun Ko,Yeongshin Jang,Sok-Kyun Han,Sang-Gug Lee 대한전자공학회 2013 Journal of semiconductor technology and science Vol.13 No.4
A low dropout regulator (LDO) with fast transient responses is presented. The proposed LDO eliminates the trade-off between slew rate and unity gain bandwidth, which are the key parameters for fast transient responses. In the proposed buffer, by changing the slew current path, the slew rate and unity gain bandwidth can be controlled independently. Implemented in 0.18- ㎛ high voltage CMOS, the proposed LDO shows up to 200 ㎃ load current with 0.2V dropout voltage for 1㎌ output capacitance. The measured maximum transient output voltage variation, minimum quiescent current at no load condition, and maximum unity gain frequency are 24 ㎷, 7.5㎂, and higher than 1 ㎒, respectively.
Load-Balance-Independent High Efficiency Single-Inductor Multiple-Output (SIMO) DC-DC Converters
Younghun Ko,Yeongshin Jang,Sok-Kyun Han,Sang-Gug Lee 대한전자공학회 2014 Journal of semiconductor technology and science Vol.14 No.3
A single-inductor multiple-output (SIMO) DC-DC converter providing buck and boost outputs with a new switching sequence is presented. In the proposed switching sequence, which does not require any additional blocks, input energy is delivered to outputs continuously by flowing current through the inductor, which leads to high conversion efficiency regardless of the balance between the buck and boost output loads. Furthermore, instead of multiple output loop compensation, only the freewheeling current feedback loop is compensated, which minimizes the number of off-chip components and nullifies the need for the equivalent series resistance (ESR) of the output capacitor for loop compensation. Therefore, power conversion efficiency and output voltage ripples can be improved and minimized, respectively. Implemented in a 0.35- μm CMOS, the proposed SIMO DC-DC converter achieves high conversion efficiency regardless of the load balance between the two outputs with maximum efficiency reaching up to 82% under heavy loads.