• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.2
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• pp.121-125
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• 2021

The machine vision technology has been widely used in the industrialized nations like the United States, Japan, and EU in the various industries from the late 1980s. Machine vision inspection system mainly consists of a camera, optics, illumination and an image acquisition system. Optimization of the illumination light source is very important. This paper shows a comparison between Pulse Width Modulation (PWM) control and strobe control in driving LED lighting system for machine vision. PWM control method has problems such as a temperature rising of LED and a flickering in image measurement for inspection. In contrast, the proposed strobe control method can suppress the temperature of LED light source below 40℃. Also, it can remove the flickering problem through a synchronization between a frame grabber and a camera shutter. Finally, the strobe control method was shown to extract clearer images with a high precision compared to PWM control method.

• Journal of Institute of Control, Robotics and Systems
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• v.22 no.5
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• pp.382-388
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• 2016

When Flat Panel Display (FPD) is made with backlight module, such as LED TV, it inherently suffers from the non-uniform backlight luminance problem that results in un-even brightness distribution throughout the TV screen. If the luminance of each pixel location of a TV screen as a function of the driving voltage can be measured, it can be used to compensate the non-uniformity of the backlight module. We use a carefully calibrated imaging system to take pictures of a TV screen at different levels of brightness and generate the compensation functions for the driving circuitry to correct the luminance level at each pixel location. Making use of the fact that the luminance of the screen is normally brightest at around the center of the screen and gradually decreases toward the border of the screen, the luminance of the whole TV screen is approximated by a mathematical function of the pixel locations. The parameters of the function are computed in the least square sense by the values of both the pixel luminance sent from the driving circuit and the grayscale value measured from the image taken by the imaging system. To justify the correction system, a simple second order polynomial function is used to approximate the luminance across the screen. When the driving circuit voltage is corrected according to the measured function, the variance of the screen luminance is reduced to one tenth of the one measured from the un-corrected TV screen.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.9
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• pp.81-88
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• 2015

LED has been great attentions in lighting industry because of its long life-time, high efficiency, excellent light output characteristics. However, the life-time of the LED driving system is decreased because of the electrolytic capacitor which is used in the power conversion system for driving LED lighting. Therefore the capacitance reduction methods have been studied to replace an electrolytic capacitor with film or tantalum capacitor. This paper presents the Single stage PFC flyback converter with the simplified third harmonic current injection circuit to reduce output capacitance and the proposed system is theoretically analyzed and verified through the experiment.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.2
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• pp.151-154
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• 2020

Radiation noise due to EMI noise generated by the driving circuits of LED lighting devices in a medical imaging room was reduced by decreasing the noise source in the driving circuits and changing the number of corrections in EMI filters. Noise attenuation and filter changes enabled driving circuits that reduced the electromagnetic waves. Such circuits were efficiently designed by using capacitors and inverters in a given space. Therefore, the malfunction of radiation devices can be minimized by using EMI-reduction filter circuits, and reliable operation of medical devices can be expected by blocking electromagnetic waves.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.393-394
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• 2015

본 논문은 다중 채널 LED(Light Emitting Diode) 구동을 위한 모듈형 전류 평형 회로를 제안한다. 기존 방식은 DC/DC 컨버터단과 다중 채널 LED 전류제어를 위해 각 채널마다 일정한 전류 제어를 하는 LED 드라이버단의 직렬 연결로 구성된다. 하지만 제안회로는 캐패시터의 전하평형원리에 의해 단일 채널 전류 제어로 모든 채널의 LED 전류를 동일하게 제어할 수 있어 DC/DC 컨버터와 LED 드라이버단을 하나로 통합한 단일 전력단 LED 구동회로 구성이 가능하며, 이는 회로구성의 단일화로 소자수 및 사이즈의 소형화가 가능하다. 또한 수동소자만으로 이루어진 모듈형 회로로써 모듈의 추가에 따라 요구되는 LED 채널 수 만큼 다채널 모듈로 확장할 수 있다. 제안회로의 타당성 검증을 위해 1kW급 LED 구동회로에 적용한 시뮬레이션 결과를 제시한다.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.8
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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.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.11
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• pp.4483-4488
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• 2010

In comparison with some other light sources, LED has merits such as long lifetime, pollution free, and high energy efficiency. Lately, due to development of LED with high brightness and capacity, LED, which has been applied in display system only, has applied in the field of lighting system. Driving current of power LED has to be controlled below the designed value. In this paper, half-bridge LLC series resonant converter, which has the current limiting function, has been described. Half-bridge LLC series resonant converter allows in relatively wide input voltage and output load range when compared to the other resonant converter. Also, it is possible to reduce a magnetic component, because leakage inductance of transformer is used as a resonant inductance. It has been validated by designing and testing 200[W] half-bridge LLC converter of DC24[V] output voltage for LED lamp driver, which includes a current limiting function and power factor correction(PFC) function.

• Journal of information and communication convergence engineering
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• v.11 no.4
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• pp.247-252
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• 2013

An intelligent light emitting diode (LED) dimming system is designed and implemented for energy-saving lighting systems. An LED light bulb is powered by an LED driver controlled by a microcontroller using pulse width modulation (PWM) signals. By changing the duty cycle of the PWM signals, the LED driver generates a driving current of up to 1,000 mA. The current consumption by the LED light bulb exhibits a very linear characteristic that indicates that the level of LED dimming can be finely tuned. Multiple sensors-lighting intensity and ultrasonic range sensors-are combined with the LED dimming system to realize an automatically controllable LED lighting system. The light intensity sensor is capable of sensing ambient light. The ultrasonic range sensor can detect objects from 0.15 to 5.6 m at a resolution of 0.0254 m. The collected information by the light intensity and ultrasonic range sensors is processed by the microcontroller that in turn automatically controls the brightness of the LED light bulb. The algorithm of the software for the LED dimming system is also described.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1025-1025
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• 2015

본 논문에는 Flyback컨버터의 PWM방식과 조명용 LED 구동장치의 디밍에 의한 조명제어를 제안한다. 제안된 LED 구동회로는 Flyback 컨버터를 이용하여 교류 입력 전원을 직류 출력전원으로 변환되는 과정을 이해한다. 포터커플러의 역할과 그 Feedback원리 그리고 PWM방식으로 IC를 직접 제어하여 버스트 디밍을 구현하고 LED의 밝기 밝기 조절 및 불필요한 전력낭비를 예방하는데 목적을 두었다.

• Proceedings of the KIEE Conference
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• 2008.10c
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• pp.248-249
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• 2008

본 논문에서는 원칩 마이크로컨트롤러를 사용한 파워 LED 구동제어 시스템의 설계 및 구현에 대해 중점적으로 기술한다. 파워 LED의 조광제어 및 특정 조도에서의 정전류 구동을 위해 전류피드백을 통한 디지털 PI 전류제어 및 PWM 구동방식을 행하였고, 시각적인 깜박거림 없는 충분한 주파수의 스위칭을 통해 부스트 컨버터를 연속도통모드로 동작시켰다. 본 논문에서 제시한 파워 LED 구동을 위한 디지털 제어시스템은 최근의 에너지 및 환경규제에 적합한 조명관련 응용분야에서 다양하게 적용될 것으로 판단된다.