Power source selection

A circuit for selecting between a primary power source and a back-up power source is provided in one embodiment. The circuit includes a first port configured to be coupled to a primary power source, a second port configured to be coupled to a back-up power source, a third port configured to be coupled to provide power to a load. The circuit also includes first and second power field effect transistors (FET) coupled between the second port and the third port, a third power FET coupled between the first port and the third port, and a dual ideal diode-OR controller coupled between the second and third power FETs to selectively turn on and off the second and third power FETs. The circuit further includes an opto-isolator coupled to a control input of the first power FET and a controller, coupled to the opto-isolator, that selectively turns on and off the opto-isolator.