Autonomous power supply

摘要

Aspects of the present disclosure are directed to providing power from two or more power sources. As may be implemented in accordance with one or more embodiments, a switching circuit includes a switching transistor connected between a backup power supply and both a primary power supply and an internal power rail. When power is provided via the primary power supply, the switching circuit operates in a blocking state in which back current is prevented from flowing to the backup power supply while the primary power supply couples power to the internal power rail. When the primary power supply is disconnected or interrupted, a voltage coupled to a gate/control terminal of the switching circuit drops and the switching circuit automatically switches to another state in which the internal power rail is powered by the backup power supply.

主权项

1. An apparatus comprising:
an internal power rail configured and arranged to provide power to circuits in the apparatus; a switching circuit including a switching transistor having a first source/drain region connected to a primary power supply circuit and to the internal power rail, having a second source/drain region connected to a backup power supply circuit, and having a control terminal coupled to the primary power supply circuit, the switching transistor being configured and arranged with the primary power supply circuit and with the backup power supply circuit to
respond to power provided via the primary power supply circuit, by automatically switching to a blocking state in which back current is prevented from flowing from the primary power supply circuit to the backup power supply circuit while the primary power supply circuit couples power to the internal power rail, andrespond to a voltage coupled to the control terminal via the primary power supply circuit and to a voltage on the primary power supply being smaller than a voltage on the backup power supply circuit, by automatically switching to another state in which the internal power rail is connected for providing power from the backup power supply circuit to the internal power rail; and another circuit configured and arranged to use power provided by the primary power supply circuit to operate the switching transistor in an OFF state by applying the voltage to the control terminal in the blocking state wherein the other circuit is configured and arranged to cease applying the voltage to the control terminal in response to power dropping on the primary power supply circuit, and wherein the switching transistor is configured and arranged to automatically switch to an ON state in response to the other circuit ceasing to apply the voltage.