a voltage detector including a voltage following circuit connected to a power supply and operable to follow a voltage value of the power supply , a selectable threshold point circuit connected to the voltage following circuit and operable to select one of a plurality of values for a threshold point of the power supply , and a switch circuit coupled to the selectable threshold point circuit and the voltage following circuit , the switch circuit cooperating with the selectable threshold point circuit to generate an output indicating whether the value of the power supply has increased above or decreased below the selected value for the threshold point in response to the followed value of the power supply .