A power supply control circuit comprising: a power input for receiving power from an external power supply; a voltage regulator coupled to the power input and providing regulated voltage to an external circuit and to the power supply control circuit itself; a first, normally-open, electrically-operated, switch coupled between ground and an active-low Enable input of the voltage regulator, a control input of the first switch coupled to the regulated voltage, such that when the voltage regulator provides the regulated voltage, the first switch is closed, coupling the Enable input of the voltage regulator to ground, keeping the voltage regulator active; a first power switching circuit providing manual activation and deactivation of the voltage regulator; a second power switching circuit providing automatic activation of the voltage regulator whenever the power input becomes powered; an intervening circuit preventing the second power switching circuit from activating the voltage regulator when the first power switching circuit has deactivated the voltage regulator, despite the continued presence of power from the external power supply on the power input; characterized in that the intervening circuit comprises a second, normally-open, electrically-operated, switch, with its source connected to ground and its drain connected to the active-low Enable input of the voltage regulator, the second switch being closed by the second power switching circuit when the second power switching circuit is first activated, and being opened by the second power switching circuit when regulated voltage is provided to the second power switching circuit. a power input for receiving power from an external power supply; a voltage regulator coupled to the power input and providing regulated voltage to an external circuit and to the power supply control circuit itself; a first, normally-open, electrically-operated, switch coupled between ground and an active-low Enable input of the voltage regulator, a control input of the first switch coupled to the regulated voltage, such that when the voltage regulator provides the regulated voltage, the first switch is closed, coupling the Enable input of the voltage regulator to ground, keeping the voltage regulator active; a first power switching circuit providing manual activation and deactivation of the voltage regulator; a second power switching circuit providing automatic activation of the voltage regulator whenever the power input becomes powered; an intervening circuit preventing the second power switching circuit from activating the voltage regulator when the first power switching circuit has deactivated the voltage regulator, despite the continued presence of power from the external power supply on the power input; characterized in that the intervening circuit comprises a second, normally-open, electrically-operated, switch, with its source connected to ground and its drain connected to the active-low Enable input of the voltage regulator, the second switch being closed by the second power switching circuit when the second power switching circuit is first activated, and being opened by the second power switching circuit when regulated voltage is provided to the second power switching circuit.