Duty cycle sequence algorithm for digitally controlled LED power systems

Abstract

High power Light Emitting Diodes (LED) of today have long life time, require low maintenance, and consume low power, which make them suitable as a general light source. Unfortunately, its high cost compared to conventional halogen or fluorescent lamps makes it difficult to be a direct replacement in the mass market. However, in the premier market, take for example a night club or an exhibition, LEDs are more favorable by performance than cost, where eye-catching by dynamic and aesthetic color is preferred. For such system, managing and mixing color requires the need for a controller, typically a Micro Controller Unit (MCU). In this thesis, the MCU in a color mixing LED system is programmed in coherent with the power stage, or Switched Mode Power Supply (SMPS), to digitally control the LED driver. SMPSs have mainly been controlled by separate analog Integrated Circuits (IC) because of their low cost, and are well known to the design engineer. However, with the cost decline in MCUs and the combination control of color and power, the proposed solution makes the system cost effective for the premier market. Moreover, the thesis focuses on implementing an algorithm to generate duty cycle that meets the performance of a double loop control scheme, using an inexpensive processor that originally cannot support with its limited clock cycle. To fully support the need for the proposed algorithm, the overall system construction with its requirements and selection criteria is explored first. Then after a brief introduction related to generating a user defined color, the main topic is explained and experimented in detail.