Schottky diodes as an OR-Gate

[chris54]

What I am trying to do is keep 12 volts to radios fed from a 12 volt power supply and 120 volt ac mains when the power goes down. using a pair of schottky diodes. Does any body have a circuit diagram I could use as a reference to learn and understand. Thanks

 

[Roff]

Do you mean you have a 12V supply powered off the mains, and a 12V battery for backup?

 

[chris54]

Yes that is just what I wanted to do.

 

[Roff]

In order for diode ORing to work, the power supply (when on) needs to have a higher output voltage than the battery. Otherwise, the battery will supply all the power.

 

[Boncuk]

Hi Chris,

if you modify the circuit using a comparator you won't have to care if you are using battery or mains power. Adjust the comparator so it will disconnect the battery if it is depleted and automatically switch to mains power supply and route the power to the circuit using a relay.

A second way would be to keep the battery connected to mains power supply at all times not exceeding the max charge voltage and operate the device in buffered mode. (Don't forget to use an extra diode to prevent current back flow from the battery into the power supply in case mains power fails.)

Boncuk