how to design circuit so that it chose power source from 12v dc or battery?

Thread Starter

ashutosh 123

Joined Feb 26, 2017
38
Hi AAC,

I have one doubt,I am designing a circuit which is having two power source 12v dc power adapter and battery.

1. How to design circuit so that by default,it take power supply from 12v dc power and if 12v dc power is not there then it would take from the battery.I don't need manual jumper and switch.

2. how to design circuit so that it will check the power source and select one which is able to drive my design.

Thanks
Ash
 

DickCappels

Joined Aug 21, 2008
8,671
This is a very common and simple approach:

upload_2017-12-1_17-43-17.png

If you use Schottky diodes instead of simple PN diodes the voltage loss will usually be very low.

How much current will the load draw?
 

AlbertHall

Joined Jun 4, 2014
11,951
If the power supply will always have a larger voltage than the battery then you can do this simply with two diodes.
Otherwise you can use the circuit below.
 

AlbertHall

Joined Jun 4, 2014
11,951
If the main supply is present it pulls up the gate voltage to be close to the source voltage (the battery voltage) and so the FET is switched off. The load receives power from the main supply through D1.

If the main supply is not present, R1 pulls the FET gate down to 0V turning on the FET so now the load receives power through the FET and D2.
 
Top