Most low-power PC design research focuses on the power consumption of devices in the system, in order to reduce the consumption of the peripheral components while the system is in the idle state. In this design, the power conversion efficiency of the multi-phase pulse width modulation power regulator can be improved by using the auto-phase switching control scheme. The external load-sensing circuit is used to both monitor the output current and to change the regulator to a different operation method automatically. This design is dependent on the different loading to set the optimised operation phase. The power conversion efficiency can be maintained from 88.19 to 93.41%, when the load current is changed from 1.06 to 119 A.