Design techniques for high efficiency high current LED drivers Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/765374602

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  • Solid-state based lighting offers a number of advantages such as long life, high efficiency and compactness compared to a conventional halogen tube based lighting. Due to these advantages they are being increasingly used in a variety of lighting applications including portable devices, home, and automotive lighting. Consequently, there has been a slew of LED drivers catering to a variety of applications. This thesis presents design techniques to improve the efficiency of high current LED drivers used in portable applications.The proposed LED driver achieves current regulation without using a series current-regulation-element. A novel, error averaged, sense-FET based current sensing technique is employed to improve the sensed current accuracy. Highly accurate and lossless current sensors and a current estimator, implemented on-chip, obviate the need for the current regulation element thereby greatly improving the converter efficiency and reducing the product cost. To maximize the efficiency and to drive the desired current over the entire battery range of a Li-Ion battery (3-5.5V), the converter operates in three different operating modes namely buck, buck-boost and boost modes. Fabricated in a 0.5um CMOS process, the converter achieves an efficiency improvement of over 13% compared to current-regulation-element based LED drivers. Measured LED current accuracy is better than 2.8% over the entire range of the battery and the standard deviation measured across 7 devices is less than 1.6%.
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