Design and Implementation of LED Driver Circuits
Date Issued
2010
Date
2010
Author(s)
Hsu, Je-Wei
Abstract
The operation principles and design considerations of source-switching adopted in the buck converter and the flyback converter to drive LEDs are fully discussed in this thesis. The central idea of source-switching technique is to cascode the power MOS on top of another transistor switch and by which we can turn on and off the power MOS by driving the bottom transistor. Theoretical analysis shows that the switching loss due to the gate to source parasitic capacitance could be largely reduced, and hence the converter efficiency can be improved. Experimental results shows that the efficiency can be improved by 1~2% compared to traditional converters, and hence the correctness of the theoretical analysis has been verified.
In another portion of this thesis, a quasi-resonant flyback converter controller is proposed. With LEDs as loading, the system can operates under constant current mode by limiting the peak current value of the primary-side inductor. As there is no need to feedback output current information, the cost, especially for the converters that require isolation, could be reduced due to a smaller number of external components used. Simulation gives a result of output current error smaller than 3% within the universal input voltage range, which is highly matched to the theoretically prediction.
Subjects
LED
Source-switching
Type
thesis
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