Best power supply (5V) from 4XAA battery holder.

[jabraham]

I'm using a LM7805T with a 4AA battery holder to supply 5V. It's less than ideal because the input voltage is supposed to be >7V (I think), and sometimes I put NiMh batteries in the holder, which give 4X1.2 = 4.8V.

So, is there a better way to get 5V consistently from a 4AA format battery holder? Or do you all use 3AA holders?

--
John

 

[westaust55]

What is the maximum load current you intend to draw.

There are a number of low drop out voltage regulators avalable with 100 mA capacity.

One such regulator is the LP2950 whcih is available in 3.0 V, 3.3 V and 5.0 V parts.
http://pdf1.alldatasheet.net/datasheet-pdf/view/9221/NSC/LP2950ACZ-5.0.html
These have a voltage dropout down to 40 mA at low currents and a max of 380 mV at 100 mA

However personnally I only use 2 cell and 3 cell AA battery holders as the primary power for battery powered projects and a 7805 1 Amp based supply for main powered (via a plug pack / wall wart) projects.

I have occassionaly used a LP2950 for 3.0V (from a 5V primary supply) for things like gLCD displays from mobile phones.

 

[inglewoodpete]

Just use a 3xAA cell holder: 4.5v works perfectly. No wasted energy.

I've also heard of people using a 4 x AA cell holder with one battery (cell) replaced with a suitably sized nail (or a piece of copper wire soldered) across the 4th battery's place.

 

[Haku]

If you need pure 5v then you could use a boost converter which gives a constant voltage output no matter what the input, there are many out there, such as: http://www.dimensionengineering.com/products/anyvolt-micro (American based) or http://www.ebay.co.uk/itm/251169704387 (China based)

 

[MFB]

As inglewoodpete suggests, you could power directly from 3XAA cells. However, without a voltage regulator there is the potential to draw damaging levels of battery current and, if the supply rail is used as the ADC reference, errors caused by normal voltage drop.

Because my PICAXE circuitry is often designed to operate from single-cell LiPo batteries (3.6V) I have adopted a 3 volt supply as standard. This seems to have few disadvantages and is compatible with a wide range of smart sensors. If you used 3XAA rather than LiPo, then 3.3 volt low drop regulators could be powered.

 

[lbenson]

lp2950 with a single 10uf electrolytic capacitor has worked well for me, 5V or 3V3.

 

[fernando_g]

If the OP really needs a regulated 5V output, from an input varying from about 6.2 to 3.6 volt (what you expect from 4 fully charged to fully depleted Alkalines) then you need a SEPIC regulator.

This is essentially a special switchmode topology which allows a regulated output voltage above or below the input voltage. Google the term.

If you are daunted about building your own switchmode converter, the other day I saw on Ebay a seller of SEPIC regulators.

 

[boriz]

Need 5v exactly?

I often prototype with 4AAs and a series diode. (The diode is only needed for alkalines. Rechargeable AAs have lower voltage).

This means I can supply a good 6v to servos and such when required. A tank capacitor downstream of the diode also helps prevent dropouts/resets etc when the motors start.