• 센서학회지
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• 제26권6호
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• pp.408-413
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• 2017

In this paper, we newly developed a byte-inverted transmission method for flicker-free visible light communication (VLC). The VLC transmitter sends original data in the former half period of the clock, and inverted data and in the latter half period of the clock. The VLC receiver receives the original data in the in the former half period of the clock. In this system, we used 480Hz clock that was generated from the 60Hz power line. The average optical power of the LED array in the transmitter is constant, thus flicker-free, in the observation time longer than the period of the clock that is about 2ms. This period is shorter than the maximum flickering time period (MFTP) of 5ms that is generally considered to be safe. This configuration is very useful in constructing indoor wireless sensor networks using LED light because it is flicker-free and does not require additional transmission channel for clock transmission.

• 대한전자공학회논문지SP
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• 제42권2호
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• pp.9-18
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• 2005

Flicker 란 인체가 느끼는 빛과 색상의 변화이다. 이런 변화는 일반적으로 일정하지 않으며 시간이 변함에 따라 변한다. 이는 눈의 피로와 두통을 일으키는 원인이 된다. Flicker 현상은 PDP를 포함하는 많은 display에 존재하며 특히 50Hz로 동작 하는 PDP의 경우에 심각한 문제를 발생시킨다. Flicker를 감소하기 위해서 많은 연구가 진행되었지만 Flicker에 대한 객관적인 정의를 내리기 어렵기 때문에 flicker에 대한 객관적인 측정방법이 필요하며 이는 display 화질 향상에 큰 도움이 될 것이다. 본 논문에서는 luminance flicker를 측정하는 수학적인 모델을 제안한다. 이 모델을 통하여 flicker가 생길 확률에 대한 정량적인 결과를 보여준다. vision 분야의 최근의 연구와 고전적인 연구결과를 적용하여 모델을 구축하였으며 인체의 눈의 임시 민감도에 초점을 맞추었다. 본 연구를 통하여 flicker-free한 PDP 개발을 위한 실제적인 툴을 만들 수 있을 것이다.

• 센서학회지
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• 제29권2호
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• pp.75-81
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• 2020

We introduce a new visible light communication (VLC) method in which three-level return-to-zero (RZ) modulation is used for flicker-free transmission. In the VLC transmitter, the three-level RZ modulation ensures that the average optical power is constant; thus, a flicker-free light-emitting diode (LED) light is achieved. In the VLC receiver, a resistor-capacitor high-pass filter is used for generating spike signals, which are used for data recovery while eliminating the 120 Hz optical noise from adjacent lighting lamps. In transmission experiments, we applied this method for wireless transmission of an air quality sensor message using the visible light of an LED array. This configuration is useful for the construction of indoor wireless sensor networks for air pollution monitoring using LED lights.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 전력전자학술대회 논문집
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• pp.161-162
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• 2013

LED(Light Emitting Diode)는 친환경적 특성, 긴 수명, 우수한 효율, 빠른 응답 속도 등의 장점이 있어 최근 기존의 백열 전등 및 형광등을 대체하는 조명 수단으로 각광받고 있다. 기존의 LED구동회로를 조광기용 MR16안정기에 연결할 경우 안정기와 조광기의 오동작으로 인해 Flicker 현상이 발생되고 선형적인 Dimming이 불가능하다. 그러므로 본 논문에서는 MR16 안정기와 조광기용 MR16안정기를 호환하는 Flicker Free LED 구동회로를 제안한다. 또한 LED구동회로의 원리와 Dimming에 따른 LED전류제어기법 원리를 설명하고 모의실험 및 시작품 제작을 통해 제안 회로의 타당성을 검증한다.

• 전기전자학회논문지
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• 제22권2호
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• pp.316-323
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• 2018

본 논문에서는 가시광통신에서 플리커를 방지하기 위한 3-레벨 바이트반전 전송방식을 새로이 소개한다. 가시광 송신부에서는 3-레벨 LED 변조기를 사용하여 원신호와 반전신호를 차례로 전송하며, 데이터 전송과정에서 LED의 평균광출력이 일정하게 유지되어 플리커가 발생하지 않는다. 가시광 수신부에서는 간단한 비교기를 사용하여 원신호가 쉽게 복구된다. 이 방식에서는 플리커 방지를 위하여 별도의 클럭이나 캐리어가 필요하지 않아 구조가 매우 간단하며, 저렴한 비용으로 플리커가 없는 실내의 가시광 시스템을 구축하는 데에 유용할 것으로 판단된다.

• 전자공학회논문지
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• 제54권6호
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• pp.123-133
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• 2017

본 논문에서는 LED 디스플레이 시스템의 동적인 구동방식에서 LPM 모듈의 구성에 관계없이 휘도구현 비트를 16비트 이내, 휘도 구현 펄스를 512개 이내에서 최적의 플리커 프리 제어 알고리즘을 개발하고 이 알고리즘을 이용하여 디스플레이 제어장치를 구현하였다. 구현방법으로는 완전한 색 표현을 위한 기존의 시프트-래치 방법을 변형하여 여러 번의 시프트-래치를 수행하게 하여 스캔횟수를 늘림으로써 리플레시율을 증가시키는 방법을 사용하였다. 그 결과로 기존의 LED 디스플레이 시스템은 리플레시율이 240~480[Hz]를 수행하지만 제안된 방법을 사용하면 리플레시율을 2,040[Hz] 이상으로 높게 구현할 수 있기 때문에 플리커 현상을 감지할 수 없게 된다.

• 전력전자학회논문지
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• 제19권4호
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• pp.327-331
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• 2014

LED(Light Emitting Diode) is a semiconductor device utilizing electroluminescent effect is a phenomenon in which a type of P-N junction diode, the light of short wavelength which a voltage is applied in the forward direction is released. LED is advantageous in reducing the energy as environmentally materials that can greatly reduce the carbon emissions, recent it has attracted attention IT(Information Technology) and GT(Green Technology) industry. In addition, there are advantages long life, high efficiency, and excellent response speed, LED have come into the spotlight as the illumination means to replace the existing fluorescent light and incandescent light bulb. When connecting to MR16 electronic transformer for existing LED driver circuit, due to malfunction of the dimmer and the electronic transformer, flicker occurs and linear dimming is not possible. Therefore, in this paper, we suggest an LED drive circuit there is no flicker with the corresponding dimming MR16 electronic transformer. Further, we explain the principles of the LED current control technique and the principle of the drive circuit of the LED, in order to validate the proposed circuit through prototyping and simulation.

• 센서학회지
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• 제27권3호
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• pp.175-181
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• 2018

In this paper, we introduce a new dimming control method in a visible light communication (VLC) system wherein byteinversion is adopted for flicker-free transmission. In the VLC transmitter, the original and the inverted data were sent sequentially and the remnant time in one period was used for the dimming control of the LED light. In the VLC receiver, only the original data was recovered using the gating signal whose width was the same as the length of the original data. In our experiments, the dimming control ranges were measured to be 22%-53%, 11%-76%, and 5%-88% of the CW LED light when the data rates were 9.6, 19.2, and 38.4 kbps, respectively. In this system, we used a 240-Hz sync pulse whose period was 4.16 ms, which was shorter than the maximum flickering time period of 5 ms that is generally considered to be safe. This configuration is very simple and useful in constructing indoor wireless sensor networks using the flicker-free LED lamps with dimming control capability.

• 센서학회지
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• 제29권3호
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• pp.180-186
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• 2020

In this study, we applied edge-pulse modulation to prevent the flicker of light-emitting diode (LED) light in a visible light identification system. In the visible light transmitter, positive pulses were transmitted at the edges of the low-to-high transition points, and negative pulses were transmitted at the edges of the high-to-low transition points of the non-return-to-zero (NRZ) data waveforms. In the visible light receiver, the NRZ waveforms were regenerated by making low-to-high and high-to-low transitions at the point of the positive and negative pulses, respectively. This method has two advantages. First, it ensures that the LED light is flicker-free because the average optical power of the LED was kept constant during data transmission in the transmitter. Second, the 120 Hz optical noise from the adjacent lighting lamps was easily cut off using a simple RC-high pass filter in the receiver.

• 센서학회지
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• 제28권3호
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• pp.191-197
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• 2019

In this study, we propose a dimming control method for a visible light communication (VLC) system, in which the subcarrier on-off keying (OOK) modulation of Manchester code is used for data transmission. In the VLC transmitter, non-return-to-zero (NRZ) code data is transformed to Manchester code, which is OOK modulated with a subcarrier. Manchester code is used for flicker-free lighting; the duty factor is changed for dimming control, and the subcarrier is used for preventing the adjacent noise light interference. In the experiments, the dimming control was carried out from about 8%-92% of the continuous wave (CW) LED light. This configuration is simple and effective in constructing a VLC system for indoor wireless sensor networks with flicker-free illumination and dimming control capability without adjacent noise light interference.