Disclosed is a power regulator for providing precisely regulated power to a microelectronic device such as a microprocessor. Improved power regulation is accomplished by optimizing the power efficiency of the power regulator. In particular, in a multiphase system, the number of active phases is increased or decreased to achieve optimum power efficiency. The multiphase voltage regulator adapts the operating mode to maximize efficiency as the load current demand of the load device changes by adjusting the number of active phases to maximize efficiency. The total value of current provided by the regulator and the total number of active phases is determined, the total number of active phases is compared with the number of active phases required to provide the total value of current at maximum efficiency; and the number of active phases is adjusted to provide the total value of current at maximum efficiency.A current sense circuit senses the current at each phase, a summing circuit coupled to the output of the current sense circuit provides the total current value of all the measured phases, a circuit coupled to the output of the summing circuit provides the time averaged total current value to a threshold detecting circuit that determines the number of phases at which the voltage regulator should be operating for maximum efficiency, and a circuit for comparing the number of phases that are operating to the number of phases at which the voltage regulator should be operating adjusts the number of active phases to the number of phases at which the voltage regulator should be operating for maximum efficiency.