• Journal of Power Electronics
• /
• 제14권4호
• /
• pp.632-640
• /
• 2014

For low-power high-frequency LED driver applications in small form factor mobile products, a high-efficiency boundary conduction mode tapped-inductor boost converter is proposed. In the proposed converter, the switch and the diode achieve soft-switching, the diode reverse-recovery is alleviated, and the switching frequency is very insensitive to output voltage variations. The circuit is quantitatively characterized, and the design guidelines are presented. Experimental results from an LED backlight driver prototype for a 14 inch notebook computer are also presented.

• Transactions on Electrical and Electronic Materials
• /
• 제17권1호
• /
• pp.21-24
• /
• 2016

A junction box used in a 3 kW photovoltaic power generation system plays a role in collecting and supplying the direct current voltage produced by photovoltaic modules to an inverter. It is also used for facilitating maintenance checks and protecting the module and inverter by keeping the voltage constant. As for the junction box, using it in a parallel connection creates a difference between the setup modules. In order to compensate, an inverse voltage diode is used. But the high-power created through the solar generator can be delivered to the inverter through the inverter regularly. Therefore, a component can break down due to excess heat. And consequently short circuits and electric leakage occurs. In this study, using a junction box that enabled the bypass of high electric power, it was possible to reduce heat generation by approximately 35℃ when compared to a standard junction box.

• Journal of Power Electronics
• /
• 제17권4호
• /
• pp.1071-1087
• /
• 2017

This paper introduces a DC/AC converter, which can be connected in parallel with a diode rectifier for regenerative applications. The DC/AC converter is supposed to transmit regenerative energy to the power grid when a motor is braking. Isolation transformers are not needed in the topology, which can reduce the size and cost. An analysis of the zero-order current existing in the system is carried out. In addition, algorithms to minimize the zero-order current, control the power factor and keep the DC bus voltage stable are discussed. A 55kW industrial prototype is built to verify the proposed analysis and control strategies.

• JSTS:Journal of Semiconductor Technology and Science
• /
• 제4권1호
• /
• pp.63-73
• /
• 2004

A simple analytical model has been presented for the study of the optical bistability using a $GaAs-Al_{0.32}Ga_{0.68}As$ multiple quantum well (MQW) p-i-n diode structure. The calculation of the optical absorption is based on a semi-emperical model which is accurately valid for a range of wells between 5 and 20 nm and the electric field F< 200kV/cm . The electric field dependent analytical expression for the responsivity is presented. An attempt has been made to derive the analytical relationship between the incident optical power ( $(P_{in})$ ) and the voltage V across the device when the diode is reverse biased by a power supply in series with a load resistor. The relationship between $P_{in}$ and $P_{out}$ (i.e. transmitted optical power) is also presented. Numerical results are presented for a typical case of well size $L_Z=10.5nm,\;barrier\;size\;L_B=9.5nm$ optical wave length l = 851.7nm and electric field F? 100kV/cm. It has been shown that for the values of $P_{in}$ within certain range, the device changes its state in such a way that corresponding to every value of $P_{in}$ , two stable states and one unstable state of V as well as of $P_{out}$ are obtained which shows the optically controlled bistable nature of the device.

• 한국레이저가공학회지
• /
• 제11권4호
• /
• pp.7-12
• /
• 2008

Laser Transformation Hardening(LTH) is one branch of the laser surface modification processes. A lot of energy is needed for the LTH process to elevate workpiece surface to temperature of the austenite transformation($A_3$), which results from utilizing a beam with a larger size and lower power density comparatively. This study is related to the surface hardening for the rod-shaped carbon steel by the high power diode laser whose beam absorptivity is better than conventional types of lasers such as $CO_2$ or Nd:YAG laser. Because a beam proceeds on the rotating specimen, the pretreated hardened-phase can be tempered and softened by the overlapping between hardened tracks. Accordingly, the longitudinal hardness measurement and observation of the micro structure was carried out for an assessment of the hardening characteristics. In addition, a hardening characteristics as a hardenability of materials was compared in the point of view of the hardness distribution and hardening depth and width.

• Journal of Power Electronics
• /
• 제16권1호
• /
• pp.84-92
• /
• 2016

Compared with Si MOSFETs, the GaN FET has many advantages in a wide band gap, high saturation drift velocity, high critical breakdown field, etc. This paper compares the electrical properties of GaN FETs and Si MOSFETs. The soft-switching condition and power loss analysis in a flyback-forward high gain DC/DC converter with a GaN FET is presented in detail. In addition, a comparison between GaN diodes and Si diodes is made. Finally, a 200W GaN FET based flyback-forward high gain DC/DC converter is established, and experimental results verify that the GaN FET is superior to the Si MOSFET in terms of switching characteristics and efficiency. They also show that the GaN diode is better than the Si diode when it comes to reverse recovery characteristics.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2007년도 제38회 하계학술대회
• /
• pp.222-223
• /
• 2007

Though there are many causes for the maximum output power reduction, the short-term problem is hot-spot effect by sun shading. To prevent this, normally PV maker uses bypass diode. In here, we tried to check the how bypass diodes works by varying sun shading portion on solar. In case of absence of bypass, the sun shading effect increases the series resistance and that promotes the reduction of maximum power and degradation of PV modules. Bypass diode worked normally when 60% of solar cell was shaded and the measured maximum output power was lower than that of theoretical one. The further analysis is needed.

• 전력전자학회논문지
• /
• 제4권3호
• /
• pp.304-309
• /
• 1999

본 논문에서는 새로운 24펄스 다이오드 정류기 시스템을 제안한다. 제안하는 다이오드 정류기 시스템은 기존의 직렬형 12펄스 다이오드 정류기에 수동의 보조회로를 추가함으로서 구성되어지고, 입력전류는 제 22차까지의 고조파가 제거되어 거의 정현파에 가까운 전류 파형을 얻는다. 또한, 출력 전압은 n=24k, k=1,2,3... 의 고조파 성분을 갖는 24펄스 특성를 나타낸다. 더욱이, 이 보조회로의 용량은 출력용량에 비하여 매우 작으며, 능동 스위칭소자를 사용하지 않으므로 외란에 강하고 구현이 간단하다. 따라서, 본 방식은 중·대용량급의 고전압 비제어(uncontrolled) 직류전원이 필요한 인버터나 무정전 전원장치등의 앞단에서 입력고조파의 저감에 경제적이고 효율적이다. 220V, 3KVA 정류기 시스템의 실험을 통하여 제안한 시스템의 타당성을 검증하였다.

• 한국광학회지
• /
• 제9권4호
• /
• pp.231-235
• /
• 1998

레이저 다이오드 뒷면 여기 방식을 이용한 Nd: YAG 레이저를 제작하고, 뒷면 여기 방식을 이용하였을 때, 들뜸 효율을 측정하였다. 포화 흡수체로 $Cr^{4+}$:YAG를 레이저 공진기 내부에 설치하여 수동형 Q-switching을 수행하였고, 그 때, 평균 출력, 펄스폭 및 반복율 특성등을 조사하였다. 수동형 Q-switching된 레이저의 펄스폭 및 반복율은 평균 출력 및 $Cr^{4+}$:YAG 결정의 낮은 강도 투과율(low intensity trasmission)에 따라 변화하였으며, 평균 출력은 최고 1 W, 펄스폭은 최저 51 nsec 까지 얻을 수 있었고 최고 약 40kHz의 고반복율로 동작하는 것을 관찰하였다.

• 반도체디스플레이기술학회지
• /
• 제17권4호
• /
• pp.37-41
• /
• 2018

$Y_3A_{l5}O_{12}:Ce^{3+},Pr^{3+}$ single crystal phosphor was prepared by floating zone method. single crystal was confirmed to have a Ia-3d (230) space group of cubic structure and showed regular morphology. The optical properties, single crystal exhibited a emission band from green, yellow wide wavelength and 610nm, 640nm red wavelength vicinity. The luminance maintenance rate was decreased by phonon with increasing temperature, but high luminance is maintained more than powder phosphor. In addition, $Y_3A_{l5}O_{12}:Ce^{3+},Pr^{3+}$ single crystal phosphor was applied to a high power blue laser diode, we implemented high power white laser lightings. and it was confirmed that thermal properties over time, due to the effective heat transfer of complete crystal structure. We confirmed that excellent radiant heat properties than powder phosphor was applied to a high power white laser diode.