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Thread: Auto-off circuit?
www.piclist.com/techref/index.htm?key=auto+off+circuit
picon face BY : Russell McMahon email (remove spam text)



>I have minimized quiescent current draw by using National Semiconductor's
>LM2936Z-5.0N ultra low power regulator.  Also, turning off the brownout
>detect configuration bit substantially lowered the current demand.



The LM2936 is my favourite regulator for micropower applications. Sadly it's
a little expensive.
However, for REALLY low quiescent current requirements it is still not good
enough - about 10 to 20 uA quiescent in pracfice AFAIR.
My power down circuit is over 100 times lower powered :-).
Of course it has the minor disadvantage of having absolutely no power
available  in off mode :-).

As a guide to when this gets important. there are 8766 hours in a year.
A 10 uA drain uses 87660 uA hrs / year or about 88 mAH.
That's a small "13" size  button cell based battery pack depending on the
chemistry used).
Or about 5% of an Alkaline AA cell.
In the latter case the loss is probably inconsequential.
In the case of the coin cell it depends on what you want your battery life
to be and how much energy you take when powered up.


   Russell McMahon

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