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3v regulated - step down from 12v

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adumas

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Hi... I'm new to the site and how those more skilled than me can help out.

I have a digital camera that takes 2 AA batteries in a battery holder. I want to externalize the power source to run from a 12v or 9v battery - so I minimize my chances of running out of power.

This needs to be a regulated 3v - and I really was hoping to find a simple chip to do this, but can't.

I have built a microcontroller circuit that flashes pictures every 10 seconds. This eventually drains the battery and fails - way before the card is filled. I'm trying to do time elapsed photography.

Can someone help me with the circuit and detail the parts that I would to buy.

I'm in a jam and would really appreciate the help!!!
 
hi,
Have a look thru this datasheet.
 
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Cool - just what I need...

I looked over the pdf/various circuit diagrams and I'm just a bit hazy about how I can regulate it...

Could/shoud I connect in series something like a 10k? pot to get my variable adjustment?

And where exactly would I put that pot? I gather from my reading that there should also be some capacitors to smooth things out...

Again, any help would be appreciated.
 
Follow the website below to get the resistor values needed to regulate the voltage.

**broken link removed**

kingpin094
 
What current does your digital camera require?

The LM317 is only suitable for 1.5A and with a 12V input it will get very hot.

Perhaps you could consider a switching requlator like the MAX649 (the datasheet can be found from Google).
 
What capacity are the batteries?

How long does it normally last between charges?

If you have both of the above then it's easy to work out the average current draw. Please bear in mind though that the peak current will be probably be slightly higher.
 
adumas,

If you have a big-enough battery, and a big-enough heatsink for a regulator, then you should just use an LM317 circuit as ericgibbs suggested (or a similar LM338 circuit if you need more current capability).

But if you want to use a switchmode supply, which would be much more efficient but a little more complex, you can have one designed completely-automatically, for you, in at least two ways:

1) Go to http://www.linear.com and download LTSpice, aka SwitcherCad, and use its File-->Switch Selector Guide menu option. It will take your input voltage and output voltage and current requirements and give you one or more schematics, and simulate them for you. (But note that I have heard rumors that the Switch Selector Guide part might now be a separate download.]

2.) Go to **broken link removed** and find their on-line Webench app and use its "Power" option, and it will do something similar to #1, but with a National IC. (You could also use this option to automatically have a linear regulator circuit designed for you, I think. And it might even also give you the specs for the heatsink that would be needed.)

In either SMPS case, you might also want to add a linear regulator like the LM317, between the SMPS and your camera, to get "extremely-clean" power. In that case, you'd want to specify the output voltage for the SMPS design to be about two volts higher than you want the output of the regulator to be.

Good luck.

- Tom Gootee

**broken link removed**

-
 
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hi adumas,
As you have the option, run it from the 9Vbty, use a LM317, on a small heatsink, use the link shown by 'kingpin' to get your 3V values,
thats all there is to it. [ you say +3V at 200mA is all you require ]

If you decide to use the 12Vbty option, lets know, tell you how to add a series resistor before the LM317 etc.

Regards

EDIT: you say 2 *AA, Depending upon the battery type this could give you = 2.4V not 3.0V.
I would suggest that you measure the AA battery voltage and adjust the LM317 to suit.
Attached a LM317 circuit for reference.

If you plan to buy a 12v rechargeable battery, I would suggest that you choose a 6v version of double the AmpHr rating.
For about the same price and size, you could double the endurance of the battery, when used with the flasher.
Remove the 22R resistor from the circuit.
 
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Have you considered using C (about 8000 mAh) or D (about 20000 mAh) batteries externally? Their output is 1.5 V. This might be an option if you're looking for long lifetime batteries.
 
You could also parallel several NiMH AA batteries.
 
Thank you all for answering - it was VERY helpful... I ended up EricGibbs diagram - it works great - I get a regulated 2.78v. Now I have to create some dummy batteries to put in the camera and then link them to the regulated board...
 
pls help me! i want to assemble circuit project...3v input invert to 12v output can you help me pls>>>>
 
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