A voltage control circuit includes a processing unit, a power control circuit, a first impedance circuit, a first switch, and a current source. The power control circuit is used for outputting a core voltage to the processing unit. The first switch and the first impedance circuit are connected in parallel between the processing unit and the power control circuit, and they feedback a feedback voltage to the power control circuit. The current source is used for providing or extracting an operating current via the first impedance circuit or the first switch. The first switch is turned on and the processing unit receives a first core voltage when the processing unit operates at a normal mode. The first switch is turned off and the processing unit receives a second core voltage when the processing unit operates at an overvoltage mode.