• Journal of Applied Reliability
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• v.12 no.3
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• pp.177-186
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• 2012

This paper presents a comparison of the failure mechanism for high power converted white LEDs(3W) with the commercially available YAG:Ce and silicate phosphor. We carry out the normal aging life test for 10,000 hours, the high temperature aging test for 8,000 hours, the high temperature and humidity aging test for 8,000 hours and the current aging testing for 5,000 hours. The optical and electrical parameters of LEDs were monitored, such as lumen, correlated color temperature (CCT), chromaticity coordinates(x, y), thermal resistance, I -V curve and spectrum intensity. The stress induced a luminous flux decay on LED in all experiments and causes a failure. So we try to find out what's a main failure mechanism for a high power LED.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2008.05a
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• pp.216-219
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• 2008

The Power LED is more much than 1W and appliable to lights that is different from signal LED. In this paper we investigated types of tests in reliability assessment standards on Power LED. we make comparison of that military standards, JEITA(Japan Electronics and Information Technology Industries Association) and JEDEC(Joint Electron Device Engineering Council) with RS(reliability standard). Reliability tests should be considered that informations can be obtained from requirements of a real system Therefore, The paper aided companies to criteria for reliability tests by themselves.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.2
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• pp.142-149
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• 2012

The independently regulated dual-output LLC resonant converter using only one power stage and one control IC is proposed in this paper. The conventional dual-output LLC resonant converter requires the extra non-isolated DC/DC converter to obtain the tightly regulated slave output voltage, which results in the low power conversion efficiency and high production costs. On the other hand, since the proposed converter controls the master and slave output voltages by pulse width modulation(PWM) and pulse frequency modulation(PFM), it can achieve tightly regulated dual output voltages without the additional non-isolated DC/DC converter. Therefore, it features a high efficiency and low cost. To confirm the validity of the proposed converter, theoretical analysis and experimental results from a 40W LED driver prototype are presented.

• The Journal of the Korea institute of electronic communication sciences
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• v.4 no.2
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• pp.123-129
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• 2009

In this study, SMPS to drive LED traffic signal light for the railroad and airport was designed and its electrical characteristics was measured. The output voltage, output current and its power efficiencies to the input voltage 8~12VAC and 8~16VDC were 6VDC, 1.85ADC and >70%, respectively. Also the power factors of the SMPS were above 0.75 in the AC input voltage range.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.230-231
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• 2013

본 논문은 형광등 안정기를 LED 조명으로 호환하기 위한 전자식 안정기 호환형 LED 구동회로를 제안한다. 제안 방식은 기존의 전자식 안정기인 LCC 공진형 인버터에 트랜스포머와 정류단의 추가해 LLCC의 공진형 컨터버로 동작시키고 해석을 한다. 회로의 특성을 분석하면 트랜스포머의 턴비와 자화 인덕턴스의 설계로 최대 전력점의 가변 및 최대전력, 링크전압의 최적 설계가 가능하다. 이론적 해석의 검증을 위하여 27W급 시작품을 제작하고 전자식 안정기와 동작하여 안정기와의 호환성 검증 및 설계와 동일한 특성을 가지고 있음을 증명하였다.

• Journal of Applied Reliability
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• v.9 no.3
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• pp.219-231
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• 2009

Power light emitting diodes(LED) for lighting fittings are so much environment-friendly, highly reliable and consume less energy that they are widely used at home and in industries such as electronics, telecommunications and industrial machineries. However, they are exposed to a very diverse environment and consists of complex components and, therefore needs careful approach to the enhancement and assessment of reliability of the item. In this article reliability assessment criteria for LED are established in terms of performance assessment test, reliability assessment test and accelerated test.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.9
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• pp.2280-2288
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• 2014

The conventional dimming control methods of LED (Light-emitting dioades) include Analog, PWM (Pulse Width Modulation), and FM (Frequency Modulation) Control. Analog dimming is controlled by adjusting forward current of Power LED. Although Analog dimming is possible to control linearly the brightness levels on a whole range (0%~100%), it comes into existence a variation of wavelength by changing the Power LED's forward current. PWM dimming has achieved by varying in duty of full current flowing to the Power LED. Generally, PWM dimming doesn't make variation of wavelength but have difficulty with adjusting the linear brightness level between 0% and 10%. FM dimming method is on the same wavelength as PWM dimming, however, it has problem of flickering at low level of dimming. This paper propose a efficient dimming control method of Power LED in order to overcome the disadvantages of the above mentioned methods. We apply to Analog method in low level of dimming control and use PWM method in dimming range from 10% to 100%. For the experiment, we design and implement a circuit and test the proposed method. Consequently, we can control the linear brightness of Power LED across the whole range and get the constant wave at different dimming level. The experimental results show the benefits of the proposed method.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.4
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• pp.358-365
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• 2011

Recently, the LED(Light Emitting Diode) replacing incandescent light bulbs and fluorescent light has great attentions as a most promising candidate for the next generation lighting source due to its environment-friendly characteristics, long life and excellent efficiency. Moreover, since it is a semiconductor device which can convert the electric energy to visible light at a very high speed, it can also used as a communication device. Therefore, the VLC(Visible Light Communication) using the LED can perform the near field communication and lighting function at the same time without additional expenses. However, since the switching device of the conventional LED driver for VLC is operated in the linear region, there exist several drawbacks such as a poor power conversion efficiency and serious heat generation. On the other hand, since the proposed driver is operated in the on/off switching region, it features a higher efficiency and more improved heat generation. To verify the validity of the proposed LED driver, experimental results from a prototype of 20W rated LED driver applied to 3MHz bps broadcasting audio system are given.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1661-1668
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• 2016

A fixed off-time controlled high power factor ac-dc LED driver is proposed in this paper, which employs a novel zero-crossing-compensation (ZCC) circuit based on a fixed off-time controlled scheme. Due to the parasitic parameters of the system, the practical waveforms have a dead region. By detecting the zero-crossing boundary, the proposed ZCC circuit compensates the control signal VCOMP within the dead region, and is invalid above this region. With further optimization of the parameters KR and Kτ of the ZCC circuit, the dead zone can be eliminated and lower THD is achieved. Finally, the chip is implemented in HHNEC 0.5μm 5V/40V HVCMOS process, and a prototype circuit, delivering 7~12W of power to several 3-W LED loads, is tested under AC input voltage ranging from 85V to 265V. The test results indicate that the average total harmonic distortion (THD) of the entire system is approximately 10%, with a minimum of 5.5%, and that the power factor is above 0.955, with a maximum of 0.999.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.2
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• pp.131-136
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• 2015

We develop the 60 W class hybrid solar LED street lamp controller. The controller is providing power via an inverter in the day with the least solar cell and battery and charging the battery for the ESS, acts as a power failure, the built-in battery. Rated output of the fabricated LED street lamp is 300 W or greater battery capacity 300 Wh, discharge time 10 hr, LED street lamp efficiency showed a very high level of light efficiency by about 127 lm/W. In addition, as a result of light distribution pattern according to the distance and the light intensity measurement will be able to ensure a very high quality, show the constant brightness in the distance from the road lights 6 m is about 35~40 lux in uniformity ratio. The proposed hybrid solar LED street lamp system showed a high energy capacity of approximately 1.5 to 152.7% power generation efficiency than typical conventional solar street lamp.