A power regulator has an input terminal to receive an input voltage, an output terminal to output an output voltage, a transistor connected to the input and terminals, a feedback terminal to receive a feedback voltage, and a control circuit to control the transistor based on the feedback voltage at the feedback terminal and a reference voltage so as to keep the output voltage constant. Various implementations include an open detection circuit to detect an open state of the feedback terminal and, on detecting the open state, to vary the reference voltage and thereby keep the transistor in an OFF state, or a voltage holding circuit configured to hold the output voltage constant at a second voltage lower than the first voltage when the feedback terminal is in an open state.