An adaptive efficiency optimized power regulator that can work at load current ranging from mille-ampere to ampere is developed for portable devices. Based on the proposed efficiency tracking method, the power regulator can adjust its efficiency to the highest as the load current or supply voltage varies. An internal 10-µA, trim-free, low temperature coefficient, supply independent current reference with process compensation feature is proposed to ensure that the system remains stable over PVT variations. Without using high gain