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I want to feed HD44780 LCD module with battery power. I use AVR controller (like ATTiny24L) and I want to make a compact device so AA batteries are too big. 3V flat battery is small enough and can feed controller but LCD wants 5V. So the question is: is there any sence in transforming 3V to 5V? Or battery life will be too short? Also if there is sence what is the right way to do it?

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You can easily make a 3V to 5V converter but if you are not used to this it can take more effort than the project you are trying to power.

You can get about 80%+ efficiency from a typical 3V to 5V converter.

IF 5 x AAA is acceptable then with a linear regulator you get about 85% energy efficiency across most of the battery range. You can also get small premade stacks of NimH cells made for cordless phones etc. 5 is less usual but probably available. These are easily recharged with a simple resistor and zener arrangement if charge time is unimportant.

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Wouldn't 4xAAA and a low-drop linear be enough (OK, maybe with a bit less lifetime..). Or smaller: two Li coin cells. – Wouter van Ooijen Feb 14 '12 at 22:43
4 x xxx cells needs 5/4=1.25V minimum + a bit more for LDO dropout. Alkaline cells will have a significant proportion of energy remaining (maybe ~= 50%). This may be acceptable. | 4 x NimH is too low. | 2 Lithium coin cells, or 4 x alkaline coin cells would work OK. – Russell McMahon Feb 14 '12 at 23:11
I`ll try 2x CR2016. It seems that would be enough. Thanks to all! – AlexZam Feb 16 '12 at 12:30
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Eveready CR2016 datasheet here. 5V for two is 90%+ of capacity = OK. Lower as current increases. Not made for more than tiny currents - be suitably aware. – Russell McMahon Feb 16 '12 at 14:01

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