In accordance with an embodiment, a method of operating a power supply includes measuring an output signal of the power supply, determining a control voltage based on the measured output signal, and determining whether a supply voltage of a voltage follower circuit is greater than a first threshold. When the supply voltage of the voltage follower circuit is greater than the first threshold, the control voltage is applied to an input of the voltage follower circuit and an output of the voltage follower circuit is applied to a control node of an output transistor in a first mode. When the supply voltage of the voltage follower circuit is not greater than the first threshold, the voltage follower circuit is shut down and the control voltage is applied to the control node of the output transistor in a second mode.