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18 September 2014 A high efficiency LED driver based on optical feedback
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Light emitting diodes (LEDs) offer durability, long life, and high efficiency that make them an excellent alternative for illumination applications. The efficiency of conventional drivers suffers from losses due to the current sensing method that they employ. In this paper, the LED array itself is used as an optical sensor by periodically measuring neighboring cells’ light intensity, instead of employing the commonly used series current-sense resistor. The results of this approach show that it provides accurate compensation of the LED characteristics, with less than one lumen variation in illumination, stability in color (color shift over time as low as ΔE = 0.76), and efficiency of up to 98.66%. The proposed sensor compensates for actual optical performance of the LED array and reduces aging effects compared to the approaches based in current measurement and control. The optical current-sensing method is a closed-loop feedback alternative, which improves the power efficiency of the LED driver by 3%. It maintains constant output illumination of the LED over time, and it utilizes a reduced number of components, thus extending the effective lifetime of LED-based devices.
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Edgar Marti-Arbona, Tino Copani, Bertan Bakkaloglu, and Sayfe Kiaei "A high efficiency LED driver based on optical feedback", Proc. SPIE 9190, Thirteenth International Conference on Solid State Lighting, 919005 (18 September 2014);

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