• Journal of Power Electronics
• /
• v.18 no.2
• /
• pp.640-650
• /
• 2018

A TRIAC dimmable LED driver with a wide tuning range and a two-stage uniform dimming scheme is proposed in this paper. To solve the restricted dimming range problem caused by the limited conduction ratio of TRIAC dimmers, a conduction ratio compensation technique is introduced, which can increase the output current up to the rated output current when the TRIAC dimmer turns to the maximum conduction ratio. For further optimization, a two-stage uniform dimming diagram with a rapid dimming curve and a slow dimming curve is designed to make the LED driver regulated visually uniform in the whole adjustable range of the TRIAC dimmer. The proposed control chip is fabricated in a TSMC $0.35{\mu}m$ 5V/650V CMOS/LDMOS process, and verified on a 21V/500mA circuit prototype. The test results show that, in the 90V/60Hz~132V/60Hz ac input range, the voltage linear regulation is 2.6%, the power factor is 99.5% and the efficiency is 83%. Moreover, in the dimming mode, the dimming rate is less than 1% when the maximum dimming current is 516mA and the minimum dimming current is only about 5mA.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
• /
• 2005.11a
• /
• pp.167-172
• /
• 2005

This study based on the experimental data on the daylight responsive dimming systems performance. The purpose of this study increases the energy-saving effects by reducing excessive intensity of radiation of artificial lighting through analyzing incident daylight. The photosensor sends amounts of detected luminous flux to digital control unit(DCU) as a signal and then, it can decide dimming ratios, by received a proper dimming signal from DCU. Generally it is effective to control artificial lighting with the different control ratio of each row by setting a photosensor as same numbers and rows as artificial lighting. However, it is ineffective to do in initial costs of systems aspect in offices. By analyzing the data of this performance and finding regular ration between photosensors. we will execute different dimming ratios to each row of artificial lighting by a single photosensor.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.21 no.1
• /
• pp.1-9
• /
• 2007

This study proposes to increase the energy-saving effects by reducing excessive intensity of radiation of artificial lighting through analyzing daylight incident. A photosensor sends amounts of detected luminous flux to digital control unit(DCU) as a signal and then, it can decide dimming ratios, received a proper dimming signal from DCU. Generally it is effective to control artificial lighting with the different control ratio of each zone by setting a photosensor as same number and rows as artificial lighting. However, it is ineffective to do in initial costs of systems aspect in offices. As a result of grasping the distribution of daylight previously and analyzing daylight and dimming data, we can dim different dimming ratios to each zone of artificial lighting by a single photosensor.

• Journal of information and communication convergence engineering
• /
• v.19 no.4
• /
• pp.269-275
• /
• 2021

Light-emitting diodes (LEDs) are modulated using a square wave pulse sequence for flicker prevention and dimming control in visible light communication (VLC). In a VLC transmitter, the high and low bits of the non-return-to-zero (NRZ) data are converted to two square waves of different frequencies, which continue for a finite time defined by the fill ratio in an NRZ bit time. As the average optical power was kept constant and independent of data transmission, the LED was flicker-free. Dimming control is carried out by changing the fill ratio of the square wave in the NRZ bit time. In the experiments, the illumination of the LED light was controlled in the range of approximately 19.2% to 96.2% of the continuous square wave modulated LED light. In the VLC receiver, a high-pass filter combined with a latch circuit was used to recover the transmitted signal while preventing noise interference from adjacent lighting lamps.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2008.10a
• /
• pp.1156-1159
• /
• 2008

Local dimming driving has advantages in reducing power consumption and improving contrast ratio(CR). In an LED backlight unit(BLU), many small LED blocks are implemented in 2-dimmensional space, and luminance of the blocks is controlled by a local dimming algorithm. However, such a BLU can induce various recognizable artifacts. A new novel algorithm is proposed for exact block luminance calculation to correct local dimming artifacts. Also we discuss modified low-gray-level dimming to achieve much aggressive power saving in a local dimming BLU system.

• Journal of the Institute of Electronics Engineers of Korea SC
• /
• v.42 no.3 s.303
• /
• pp.63-70
• /
• 2005

The electrodeless lamps using the induction discharge have a long lifetime and a high tolerance for the variable output conditions of a ballast since they don't need the electrodes. This paper proposed two novel dimming algorithms for the Electrodeless lamps and described the resonant inverter adopted the proposed methods. The proposed dimming algorithms are based on the conventional burst dimming method which is normally adopted for LCD back-lights. One of the proposed algorithms is a improved burst dimming method, which controls the illumination by duty ratio of $5\%$ and its control circuit is formed by simple digital logics. The other algorithm is a burst PWM average duty ratio control method, which controls the illumination by duty ratio of $1\%$ and its control circuit is formed by more complex digital logics than the first method. To verify the validity of the proposed dimming methods, a prototype experimental setup for 100W Electrodeless lamps is carried out and its results are presented in this paper.

• Proceedings of the IEEK Conference
• /
• 2003.07c
• /
• pp.2847-2850
• /
• 2003

A input voltage conversion dimming control formula and a PMW dimming control formula which have been used for dimming control of CCFL driving inverter in TFT-LCD backlight, are the existing facilities so far, however, in this thesis the circuit is designed by applying The rover inverter that are able to measure output brightness according to changing of duty ratio at PWM and voltage. consequently, it's able to be confirmed that we can have dimming control more detailed than before.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.50 no.8
• /
• pp.128-135
• /
• 2013

This paper presents a high dimming ratio Power-LED driver IC with high power which is capable of controlling LEDs. In order to accomplish a high dimming ratio LED driver, the preloading inductor current methodology is proposed for the power stage of the proposed method to achieve the fast transient response time during the Power-LED load switching. The information containing the current flowing on the LEDs can be utilized to predict the amount of the current on the inductor. The minimum LED current rising time of existing high dimming ratio Power-LED driver is limited by $3{\mu}s$, however that of the proposed high dimming ratio Power-LED driver is reduced about 1/10. The LED driver is implemented with 0.35um 60V BCDMOS 2-poly 4-metal process. The measurement results show that the proposed LED driver system features the minimum rising time as small as 240ns at the dimming frequency of 1KHz with a 12V of input voltage, nine white LEDs and 353mA of LED current. The LED rising time and power conversion efficiency of the chip are measured to be 240ns and 93.72%, respectively.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2009.10a
• /
• pp.972-974
• /
• 2009

This paper presents smart regional contrast enhancement technique of partitioned image for local dimming backlight on small-sized mobile display to reach two goals. One is to save the power consumption, and the other to improve contrast ratio of display image. Recently new advanced method is proposed, named local dimming method, that backlight LED is positioned on backside of the display panel. So it is important to partition an image by sub blocks and then post-processing independantly. This means regional contrast enhancement. After partitioning, we compare the mean luminance(Y) value of each sub-block image with the one of original whole image. If some blocks have the mean value lower than the one of whole image, they are processed with the proposed method and others are bypassed. Simultaneously the information of the processed blocks are transferred to BLC(Backlight LED Controller). And then the supply current of each backlight LED is reduced to realize the contrast ratio enhancement and at the same time to power consumption reduction. In addition, we verify this proposed method is free from blocking artifacts.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2008.10a
• /
• pp.769-772
• /
• 2008

For several years, many researchers have proposed LED backlight dimming technology for low power consumption and high contrast ratio. One of the major issues plaguing RGB LED with 2D dimming technology is color shift. This undesirable variation makes it difficult to use RGB LED as light sources in the backlight system. This paper describes the useful method of the optical feedback system for 2D dimming RGB LED backlight. The test results show that our proposed method is very suitable for the 2D dimming technology.