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방열 조건에 따른 5W급 고출력 백색 LED 모듈의 광 특성 평가
윤장희(Janghee Yun),염정덕(Jeongduk Ryeom) 한국조명·전기설비학회 2012 조명·전기설비학회논문지 Vol.26 No.12
The performance and lighting characteristics of the LED depend on cooling condition because the power LED generates lots of heat. In this paper, the effect of the generated heat from power LED module on lighting characteristics and performance is measured and evaluated. For experiments, the transient temperature of a power LED module with cooling condition is measured. In addition, the temperature and lighting characteristics of the LED module are measured during the steady state. As a result, the cooling condition is less effective on the lighting characteristics of the LED module at rated current but the cooling condition extremely affects those of the LED module over the rated current. Because high temperature of the power LED module causes the low phosphor conversion, luminance efficiency becomes low and color temperature becomes high. When power LED module are driven over the rated condition, higher temperature is directly related to lighting characteristics and performance of the LED module rather than higher current.
윤장희(Janghee Yun),유성호(Sungho Yoo),염정덕(Jeongduk Ryeom) 한국조명·전기설비학회 2012 조명·전기설비학회논문지 Vol.26 No.8
In this paper, a new LED driving circuit which is able to control dimming of LED is proposed using charge pump. The proposed LED driving circuit steps down the input voltage to operate LED without DC-DC converter. The operation of this driving circuit is verified by P-Spice simulation, and the characteristics of the driving circuit is measured and evaluated in the experiments. As a result, the driving circuit efficiency of 88.5[%] is obtained when all LEDs are turned on by digital control method at the highest dimming level(255/255).
고출력 백색 LED 램프의 구동조건에 따른 온도 및 광 특성 평가
윤장희(Janghee Yun),염정덕(Jeongduk Ryeom) 한국조명·전기설비학회 2011 조명·전기설비학회논문지 Vol.25 No.11
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.
윤장희(Janghee Yun),강신호(Shinho Kang),이정섭(Jeongseop Lee),염정덕(Jeongduk Ryeom) 한국조명·전기설비학회 2010 한국조명·전기설비학회 학술대회논문집 Vol.2010 No.5월
기존의 조명을 LED가 대체 하면서 조명용 LED의 발열이 문제되고 있다. 본 논문에서는 상용화된 LED 램프에 흐르는 전류와 이때 발생하는 열이 LED의 광특성에 어떠한 영향을 주는지에 대한 실험을 하였다. 실험에서 LED 구동회로와 디지털 논리회로를 제작하고 일정한 시비율에서 임의의 주파수에 대한 LED의 조도와 온도의 변화를 비교하였다. 그리고 일정한 조도에서 전류에 대한 LED의 온도 변화를 비교하였다. 본 연구에서 얻은 결과를 통하여 평균전류가 같더라도 LED에 흐르는 펄스 전류가 높을수록 온도가 많이 올라가고 조도가 상당히 저하하는 것을 알 수 있었다.
윤장희(Janghee Yun),유성호(Sungho Yoo),이정훈(Jeonghun Lee),염정덕(Jeongduk Ryeom) 한국조명·전기설비학회 2011 한국조명·전기설비학회 학술대회논문집 Vol.2011 No.5월
조명용 LED의 광출력이 높아짐에 따라 발열이 문제되고 있다. 본 논문에서는 LED의 전류와 이때 발생하는 열이 LED의 광특성에 미치는 영향을 측정, 평가 하였다. 실험에서 정격 전류 범위 안에서 평균전류가 일정할 때 최대전류에 대한 LED의 온도와 휘도의 변화를 측정 하였다. 그리고 DC 구동전류를 증가시키면서 LED의 온도와 휘도 변화를 측정하였다. 본 연구의 결과로부터 평균전류가 정격전류 이하일 때에는 LED의 발열이 광출력에 미치는 영향은 미미하지만, 그 이상의 범위에서는 발열이 광출력에 상당한 영향을 주는 것을 알 수 있다.
선택적 충전방식 전하펌프를 사용한 LED 램프 조광구동 기술
김재현(Jaehyun Kim),윤장희(Janghee Yun),염정덕(Jeongduk Ryeom) 한국조명·전기설비학회 2013 조명·전기설비학회논문지 Vol.27 No.9
A new LED lamp driving technology with a charge pump instead of a conventional DC-DC converter is proposed. The proposed driving technology is used to control the LED lamp with digital dimming. The power loss in the zener diodes is reduced because the charging process of the capacitors is selectively controlled according to the digital control signal. From the experimental results, when dimming four LED lamps simultaneously, the average driving circuit efficiency of 89% is obtained, regardless of the dimming level. White light with color temperature over a range of 2800∼7200K was produced by dimming control of red, green, blue and amber LED lamps with the proposed driving circuit. The characteristics of the driving circuits can be changed depending on the characteristics of the R, G, B, and A LED lamps. The efficiency of the driving circuits up to a maximum 89% can also be obtained depending on the combination of LED lamps. The driving technology with digital dimming control for LED lamps proposed in this paper would be effective for obtaining high efficiency in LED driving circuits and remote control of LED lamps using digital communications.
김도영(Doyoung Kim),윤장희(Janghee Yun),염정덕(Jeongduk Ryeom) 한국조명·전기설비학회 2013 조명·전기설비학회논문지 Vol.27 No.7
LED lamps are appropriate to the light source for use in broadcasting lighting. When the lighting frequency of LED lamp is different from the shutter frequency of camera, however, the flicker appears on the moving image which is taken by the camera under the dimmed light of LED lamp with conventional dimming methods. In this study, a new dimming method for the LED lamps used as the broadcasting lighting is proposed to minimize the flicker. A lighting period in the proposed dimming method is divided into the several sub-periods which have weight of the bits. Also, the proposed dimming method has characteristics that are optimizing the turn-on timings of two LED lamps to reduce the turn-off periods of the lamps and not to overlap the turn-on periods of the lamps. In the experiments, the incidence of the flicker is taken by the camera under several lighting conditions of the conventional dimming methods and the proposed dimming method. In addition, the brightness values of the frames are obtained in the moving image, and incidence of the flicker is evaluated and compared with conventional methods. From the results, the incidence of the flicker in the proposed method is more improved than the conventional methods.
이정섭(Jeongseop Lee),윤장희(Janghee Yun),강신호(Shinho Kang),염정덕(Jeongduk Ryeom) 한국조명·전기설비학회 2010 한국조명·전기설비학회 학술대회논문집 Vol.2010 No.9월
실험용 PDP에 이동하는 두 계조의 경계를 표시하고 이를 추적 촬영하는 동화상 의사윤곽 노이즈 측정/평가 시스템을 개발하였다. 개발된 시스템으로 측정한 결과, 두 계조의 배열에 따라 두 계조의 경계에 어둡거나 밝은 띠의 노이즈가 나타났으며, 이동속도가 빨라질수록 노이즈의 범위가 확대됨을 확인 할 수 있었다. 또한 이 노이즈는 CCD 센서를 정지시켰을 경우에는 측정되지 않았다. 이 결과들은 기존의 연구결과와도 잘 일치하므로 본 연구에서 개발한 측정 시스템은 PDP의 의사윤곽 노이즈를 정량적으로 평가하는 데 유용하다.