• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.590-593
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• 2009

In the 2D local dimmable LED backlight system, each LED segment can be controlled separately. This can enhance the contrast ratio and reduce overall power consumption of LCDs. However, an artifact such as 'halo mura' can be observed around the bright object in the dark background. This is caused by the light leakage from the bright area into the dark one. Therefore, the 'halo mura' can be more easily observed in the oblique viewing direction. Thus, in this study, the perceivable degree of the halo mura is evaluated according to the level of the off-axis light leakage of LCDs. It is found that an acceptable degree of halo mura can be obtained in 2.0 cd/$m^2$ of the diagonal light leakage. In addition, the halo mura is unperceivable under 0.7 cd/$m^2$ of the diagonal light leakage which can be achieved with optimally compensated polarizers.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.938_939
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• 2009

LED에 대한 관심과 개발이 지속되고 있는 현재 그 활용이 LCD 패널, 실내 외 조명등 실생활에 많이 이용되고 있다. 특히 실내 조명에서는 적용이 용이 하기 때문에 백열등과 형광등의 대체로 LED를 사용한다. 본 논문에서는 실내 조명 에너지 절감을 위하여 백열등 대체용 Triac 조도 제어 POWER LED 구동회로를 소개한다. Triac 위상 제어 회로는 백열등 전용으로 만들어 진 것이 대 다수이고 실내 조도 제어를 위해 많이 설치 되어 있다. Triac 위상 제어를 위한 POWER LED 구동 회로는 에너지 절감은 물론 백열등 대체 시 Triac 위상 제어 회로를 그대로 사용 할 수 있기 때문에 사회 전반에 걸쳐 사용 될 것으로 사료된다.

• 전기학회논문지
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• 제61권8호
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• pp.1130-1139
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• 2012

This paper proposes a LED lighting system using integrated power system composed of bridgeless PFC, LLC DC-DC transformer, and dimmable constant current LED driver module. The proposed LED lighting system features high efficiency, high power factor, and dimming capability. In order to verify the validity of the proposed system, the 2kW prototype system was built and tested. From the experimental results, it was confirmed that the maximun efficiency of 92.6% and maximum power factor of 99.7% can be achieved.

• 전력전자학회논문지
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• 제19권4호
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• pp.297-302
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• 2014

In this paper, a LED driver compatible with TRIAC-dimmer applying active bleeder is proposed. If TRIAC-dimmer is connected with LED driver, flicker phenomenon occurs by TRIAC malfunction. In order to prevent this problem, a current over holding current must flow into TRIAC. Therefore, additional circuit compatible with TRIAC-dimmer is required to provide enough current. Passive bleeder has power loss in whole operation period. The proposed circuit apply a valley-fill circuit for power-factor-correction and a novel active bleeder detecting malfunction point of TRIAC. Therefore, it prevent malfunction of TRIAC-dimmer and have advantage of higher efficiency than passive bleeder. To verify the validity of proposed circuit, 13W-lighting LED driver prototype has been proposed.

• 한국정보기술학회 영문논문지
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• 제9권2호
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• pp.75-87
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• 2019

This paper presents a fully digital controlled power supply unit for the wireless controlled dimmable LED lighting system. The proposed power supply designed using a fly-back converter, which is directly controlled by a microprocessor. Although the proposed circuit does not sense the AC input current and has not AC input voltage feed-forward, it can achieve a high power factor. The proposed power supply directly regulates the output power for LED loads using the PWM and PFM control of the fly-back converter without additional regulator. For a wireless remote control function, the Zigbee modem is equipped in the proposed power supply. A prototype set-up has been built and tested. Through the experiment with a prototype set-up, the usefulness of the proposed power supply is verified.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2018년도 전력전자학술대회
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• pp.210-212
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• 2018

A new switching mode has been proposed to obtain high power factor and low THD in single stage AC-DC converter. The conventional voltage mode control in critical conduction mode distorts input current shape with poor THD in flyback topology. Once TRIAC dimmer is connected, visible flicker in the LED lamp is easily detected due to a lack of TRAIC holding current near the input voltage zero cross. The newly proposed method can shape the input current by providing a desired reference voltage so that low THD is obtained by ideal sinusoidal input current in case of no dimmer connection and flat input current performs good TRIAC dimmer compatibility in phase-cut dimming condition. To confirm the validity of the proposed method, theoretical analysis and experimental result from 8W dimmable LED lighting system are presented.

• Journal of the Optical Society of Korea
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• 제18권5호
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• pp.459-465
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• 2014

Visible light communications (VLC) using the intensity modulation of light-emitting diodes (LEDs) provides a new communication medium to overcome the shortage of radio spectrum, and allows reuse of LED lighting infrastructures. Orthogonal frequency-division multiplexing (OFDM) was introduced to VLC for its merits in mitigating the fading effects resulting from delay spread, and in avoiding low-frequency ambient interference. Noise and clipping are two major factors that degrade the performance of OFDM in VLC. A larger signal easily overcomes noise, but experiences impairment by clipping. Therefore, degradation due to clipping has a trade-off relationship with that due to noise, depending on the signal amplitude of OFDM. In this paper, the optimal signal amplitude in the trade-off is obtained by simulation when the dimming and LED intensity are given. The former indicates a user's requirement for lighting, and the latter represents the channel quality. The required LED intensity-to-noise ratio, as the channel quality that guarantees dimming as well as an adequate bit-error rate (BER), is also discussed.

• 한국통신학회논문지
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• 제40권2호
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• pp.385-389
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• 2015

배경 잡음이 강한 실내 환경에서 가시광통신을 이용하기 위해서는 저주파대역 잡음을 피해야 한다. 또한 통신을 하면서도 LED 조명의 장점을 유지하기 위해서는 조명등의 깜박임이 없어야 하며, 밝기를 조절할 수 있어야 한다. 본 논문에서는 위 기능을 수행하기 위해 신호 스펙트럼을 고주파 영역으로 이동하여 전송을 수행하였다. 특히 송수신을 모두 디지털회로만으로 구현 가능하도록 Subpulse-VPPM 변조방법을 제안하고, 전송 성능 측정을 위해 테스트베드를 제작하였다.

• ETRI Journal
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• 제36권6호
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• pp.905-912
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• 2014

In this paper, a new architecture is proposed to achieve complexity efficiency in implementing variable pulse position modulation (VPPM). VPPM, specified in IEEE 802.15.7, can support wireless communication and dimming control simultaneously using visible light. The proposed architecture is based on the VPPM signal property in which the transition point of the modulated output is obtained by counting the sample index and comparing it to both the assigned dimming factor and the transmitting data. Therefore, the proposed architecture can be composed of simple logics, including a counter, a comparator, and an inverter, all of which are insensitive to the dimming resolution in contrast to a conventional codeword-table method. This paper describes the verification of the proposed algorithm through a register-transfer level implementation of the codeword and proposed architectures. In comparison with the codeword-table method, the proposed method gains a nine-fold complexity reduction at a 1% dimming-step resolution.