Hello
this is my first post on this forum.
what i want to do is make a UPS like circuit to provide my arduino with backup power when the main power supply fails. But i don't want to recharge the batteries. Because I have read in this forum that trickle charging requires additional circuits to control and it may reduce the life time of the battery.
my power requirement is very low. around 10mA for few seconds at a time. I will save variable values to eeprom put the arduino to seep after that. Hopefully I can use two AA batteries for around a year before changing them,
My electronic knowledge is limited. I drew a simple circuit for this application. What i want is to know if it is correct. Will it switch from main power to battery power when main power fails. Is there any thing I need to change ?????
your help will be highly appreciated.

 

Alkaline AA batteries are just 1.5V, so you would need 4 of them to give you 6V.
This would be dropped to about 5.3V by the 1N4007 diode (it has about a 0.7V forward drop).

But note that this diode drop will also reduce the 5V regulator output to about 4.3V.
You might want to change the regulator to the 6V 7806 so that the output to the Arduino will be about 5.3V also.

Alternately you could eliminate the diode in series with the output of the 7805 and connect it from the output (diode anode) to the input (cathode).
That will prevent any damage to the 7805 when it is unpowered and the battery is providing the voltage.
That will give better 5V regulation from the regulator.