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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