Adaptive Fail-Save Power-On Control Circuit

A circuit includes an 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, and a first switch coupled between ground and an Enable input of the voltage regulator. A control input of the first switch is coupled to the regulated voltage, such that when the voltage regulator provides regulated voltage, the first switch is closed, coupling the Enable input to ground, keeping the voltage regulator active. A first switching circuit provides manual activation and deactivation of the voltage regulator; a second switching circuit provides automatic activation of the voltage regulator whenever the power input becomes powered. An intervening circuit prevents the second switching circuit from activating the voltage regulator when the first switching circuit has deactivated it, despite the continued presence of the external power supply.