battery secondary power

[RajTS]

Hi,

I am new here. I have a very basic question, maybe bordering on Dumb.. but couldn't see the answer in previous questions.

My board will normally be working on AC power with an AC-DC converter. (i.e, not portable). When power fails, I want a battery backup ONLY to keep the RTC ticking. Planning for a Non-rechargable (2 x AA size battery). What would be the best way to conserve battery? I mean, battery should be drained only when there is no power. Should I just use two diodes ? (I'll try to upload a simple pic.. Thing is I just switched to Mac.. Yet learning to get around) Or is there some other ingenious way to do it?

Thank you for any suggestions you can provide.

-Raj

[Jared]

Hi,

Are you using a custom board or a development kit?

regards

Jared 

[RajTS]

As of now, the development kit. But I may go for a custom PCB. (Already have some samples)

On other uC's, I'd just go for a diode.. as in this picture. (Not withstanding the voltage drop across the diode). But would like to try any better option.

Thanks a Lot.

[Jared]

Hi,

I can't see any reasons for this not to work for the nRF52 series. But how you make sure that the battery isn't drained during normal operation?

regards

Jared 

[RajTS]

No I can't. I can only make sure that the Ac-Dc and Battery won't leak onto one another. Not exactly make sure that battery is conserved. Hence this query..

And with 52810, I don't plan to have a separate RTC chip..

Is there a proven/standard design/solution to what I am trying to do?

Thank You

Raj

[Jared]

RajTS said:

No I can't. I can only make sure that the Ac-Dc and Battery won't leak onto one another. Not exactly make sure that battery is conserved. Hence this query..

I see... Have you looked at using a comparator and a transistor instead of a diode? You could use the comparator to monitor the AC/DC voltage and then turn on the transistor when the voltage from the converter falls.

regards

Jared 

[RajTS]

MOSFET, not Transistor, you mean? Instead of the second diode.. We may not need a comparator exactly.. Or use the on-chip ADC.. Still there may be a VERY brief instance it could draw from both sources, but I believe that is better than losing power for a brief instance. I need to study about it a bit more.

Thank You