A device suitable for use as an electrical analog of a unidirectional mechanical valve includes a three-terminal MOSFET. A sensing comparator has inputs coupled to the drain and source terminals of the FET, and an output coupled to the gate of the FET. A floating power supply allows the analog to operate independently of the circuit in which it is used. The FET will conduct current whenever the voltage from the drain to the source exceeds a threshold value, and will effectively act as an open circuit whenever the drain to source voltage is less than this threshold.
Carl E. Edlund