A ballast used with an input power source for energizing a lamp. The ballast includes a power stage, a controller, an internal power supply for the power stage and the controller, and an input switch. The power stage energizes the lamp with power supplied by the input power source. The internal power supply is connected to the power stage for receiving power from the power stage and is connected to the input power source via the input switch for receiving power from the input power supply when the input switch operates in a closed mode. When the input switch operates in an open mode it electrically disconnects the internal power supply from the input power source. The controller selectively operates the input switch in the open mode and the closed mode as a function of the voltage of the internal power supply while the lamp is energized.