Patent ID: 7646115

Claim:
A regulator circuit configured to operate with multiple power supplies, the regulator circuit comprising: an input terminal configured to receive an input voltage; an output terminal configured to provide a regulated output voltage, wherein the regulated output voltage is a function of the input voltage; a first driver having a driver output coupled to the output terminal and configured to provide the regulated output voltage when active, the first driver further having a supply terminal coupled to a high power supply; a second driver having a driver output coupled to the output terminal and configured to provide the regulated output voltage when active, the second driver further having a supply terminal coupled to a low power supply; and a first circuit operable to select between the first driver and the second driver, and enable either the first driver output or the second driver output to be active according to which driver has been selected; wherein the first circuit is further operable to compare the input voltage with a control voltage that has a magnitude just below a magnitude of the low power supply, to determine which driver to select.