• Journal of Power Electronics
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• v.14 no.2
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• pp.257-264
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• 2014

A novel converter-free AC LED driver that is highly resistant to the fluctuation of AC voltage is proposed in this study. By removing large passive components, such as the bulky capacitor and the large-value inductor, the integration of the driver circuit is enhanced while the driving current remains stable. The proposed circuit provides LED lamps with a driving current that can follow the sinusoid waveform to obtain a very high power factor (PF) and low total harmonic distortion (THD). The LED input current produced by this driving current is insensitive to fluctuations in the AC voltage. Users will thus not feel that LED lamps are flashing during the fluctuation. Experiment results indicate that the proposed system can obtain PF of 0.999 and THD as low as 3.3% for a five-string 6 W LED load under 220 V at 50 Hz.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.1
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• pp.42-48
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• 2016

Light-emitting diode (LED) drivers are recently replacing fluorescent lamps; these drivers can operate adaptively with various ballasts without modifying and removing such ballasts. To satisfy these trends, a LED driver that is compatible with both electronic and magnetic ballasts is proposed in this study. Unlike conventional LED drivers, the proposed driver has a ballast recognition circuit and a mode selection circuit to operate ballasts at optimal conditions. Therefore, it features low voltage stress, high efficiency, and good compatibility with both electronic and magnetic ballasts. Moreover, it can be compatible with a wide selection of ballasts from various manufacturers. To confirm the validity of the proposed LED driver, results of the theoretical analysis and experimental verification performed on a 15 W-rated prototype are presented.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.11
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• pp.33-38
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• 2011

In this paper, the effect of pulse current and generated heat on characteristics of the LED is measured and evaluated. For experiments, the LED driving circuit and digital logic which determines period and duty ratio of lighting are designed. At rated current, the temperature and optical characteristics of the LED with change in duty ratio and period are compared, and those of the LED with change in duty ratio and existence of cooling fan are also compared at constant average current. As a result, frequency does not affect device temperature and optical characteristic of the LED but duty ratio does. Also, the cooling fan is less effective on those of the LED at rated current.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.250-251
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• 2010

최근 각광받고 있는 LED의 긴 수명시간에 비해서 전원 장치의 짧은 수명시간 문제가 크게 대두되고 있다. 이에 본 논문에서는 전원 장치의 수명시간을 좌우하는 전해 커패시터를 대체하여 용량이 매우 작은 필름 커패시터를 사용함으로써 전원 장치의 수명시간을 연장하고 원가를 절감 하고자 한다. 또한 PFC기능을 추가하여 역률을 향상 시키고자 한다. 고압 LED구동을 위한 20W급 비절연형 부스트 컨버터와 벅부스트 컨버터 역률 보상 전원 장치를 설계 및 제작하고 실험을 통해서 제안된 토폴로지의 타당성을 검증하였다.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.358-359
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• 2013

LED는 우수한 특성으로 인하여 차세대 조명으로 각광받고 있지만, 높은 비용에 따른 시장 활성화가 더딘 상태로서 저가격화 노력이 꾸준히 이루어지고 있다. 현재는 LED조명을 구동하기 위한 정전류 Driver, AC-DC컨버터를 배제시킬 수 있도록 AC 입력으로 LED를 구동하는 기술이 선보이고 있지만, AC성분 특성상 낮은 효율과 역률, 높은 THD의 문제점을 가지고 있다. 본 논문에서는 직렬 콘덴서를 통해 AC 입력전압으로 LED를 구동하는 방식에서 입출력변동에 따른 정전류 제어와 높은 THD를 개선하기 위한 스위칭 기법을 제안하였고, 이러한 회로의 용량성 역률을 보상하기 위하여 유도성 부하인 방전램프(고압나트륨램프)와 결합을 통한 역률을 보상하는 하이브리드 조명회로를 제안하였다.

• Journal of computational fluids engineering
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• v.18 no.1
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• pp.63-68
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• 2013

The purpose of this study is to investigate the cooling performance of radial heat sink used for high power LED lightings by natural convection cooling with surrounding air. Experimental and numerical analyses are carried out together. Parametric studies are performed to compare the effects of geometric parameters in radial heat sink such as the number of fins, fin height, fin length, and thickness of fin base as well as the surface coatings of radial heat sink. In this study, the cooling of 60 W LED lamp is examined with radiative heat transfer considered as well as natural convection. Numerical results show the optimum condition when the number of fin is 40, heat sink height is 120 mm, fin length is 15 mm, and fin base thickness is 3 mm. The difference in temperature of the LED metal PCB is within $1^{\circ}C$ between numerical analyses and experimental results. Also, the CNT coating on the heat sink surface is found to increase the cooling performance significantly.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.9 no.4
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• pp.43-51
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• 2010

In this paper, we studied line coding technology tendency for high speed data communication at LED-ID (Identification) communication system in indoor environment. A LED-ID technology is a communication using visible ray (RGB) that come out in LED device. It is energy curtailment effect and possible in ubiquitous network service applications. The LED-ID system has the above advantages about that the communication throughout the whole room is enabled by high power lighting and lighting equipment with white colored LED which are easy to install and have good outward appearance. Therefore, the transmission by light waves is more suitable for wireless networks than by radio waves. We compared with the NRZ, AMI, 4B5B, HDB3, 8B10B line coding for efficient in error detection and serves data transmission of high speed.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1516-1517
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• 2007

This paper investigated the breakdown effect of the CMOS device by impact of high power electromagnetic wave. The experiments employed a waveguide to study the current characteristics of CMOS device broken by high power electromagnetic wave. The CMOS device were composed of a LED drive circuit for visual discernment. Also CMOS device broken by high power electromagnetic wave was observed by power current. The CMOS device were broke by high power electromagnetic wave at about 10 kV/m and when power current is 75 mA. Based on the result, CMOS devices should show plan to protect the CMOS devices by high power electromagnetic wave. And the database from this experiment should provide the basis for future investigation.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.2
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• pp.137-143
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• 2015

This paper presents the intra capacitance modeling based on the winding method and section bobbin for CM choke capable of EMI attenuation of broad bands from lower to higher frequency bands and high frequency type common-mode choke capable of EMI attenuation of high frequency band used in the EMI Block of LED-TV SMPS. The case of high frequency type CM choke can be explained by the parasitic capacitance of three types of CM choke. The winding method of section bobbin type is smaller than the others. The first resonant frequency of the proposed CM choke tends to increase as the parasitic capacitance becomes small and its impedance characteristics improved performance as the first resonant frequency increases. The CM chokes of the proposed section bobbin type shows that in the future, the method may have practical use in LED/LCD-TV SMPS and in several applications, such as LED lighting, adapters, and so on.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1661-1662
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• 2006

고출력 LED의 전기적 광학적 열적인 특성을 분석한 결과를 토대로 MCPCB를 사용하지 않고 전구 형태의 좁은 면적에 고출력 1W LED를 배열하고, 적외선 카메라와 ICEPAK(열유동해석 프로그램)을 이용하여 14개의 LED 배열에 대한 LED 전구의 최적방열 및 기구 설계를 실시하였다. LED 전구에 대한 정전압과 정전류 제어방식의 고효율 구동회로를 제작하여, 약 70% 이상의 회로 효율과 약 95% 이상의 고역률, 약 20lm/W 이상의 고효율 LED 전구를 실현하였다. 정전압 구동회로는 동작시간에 무관하게 일정한 광출력을 나타내며, 정전류 구동회로는 초기 시동시 높은 광출력을 나타내고 동작시간의 경과에 따라 광출력 감소율이 높게 나타냄을 알 수 있다.