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This paper focuses on effective system modeling and implementation of a dc-dc buck converter with a digital controller. Two methods are systematically followed to design a two pole, two zero proportional-integral-derivative (PID) controller. Method one uses a traditional design by emulation, where compensator poles and zeroes are chosen based on the uncompensated loop response to yield sufficient phase and gain margins for system stability. Method two uses a direct digital design method. Further, a design topology based on a supervisory loop concept using and Implicit Model Adaptive Controller to augment the digital PID counterpart is explained. This augmentation is necessary when there are parametric variations in the system. Finally, controller coefficients from both methods are implemented on a practical 66 W buck converter hardware platform and the results are satisfactory.