A switching buck regulator is required if you wish it to be more efficient.
Roman Black designed a simple, efficient switching regulator using discrete
components. His design is for less than half an amp, but you might be able to
beef it up with the appropriate components. He designed it specifically as
something simple and efficient to replace the 7805:
http://www.romanblack.com/smps/smps.htm

Or you could use a PWM IC and skip most of the experimentation. For instance,
the venerable TI TL494:
http://focus.ti.com/docs/prod/folders/print/tl494.html

Design example includes a 5V/10A buck SMPS:
http://focus.ti.com/lit/an/slva001d/slva001d.pdf

Or chips from National Semiconductor:
http://www.national.com/analog/power/switchers

Maxim has a lot of PWM chips and they have free samples available:
http://www.maxim-ic.com

For 12V regulated, stepping up (boost) is one thing, stepping down (buck) is
another. But doing the buck-boost thing, where the input voltage may be above
-or- below the output, gets a bit more complicated. However, there are ICs made
just for that.

Steve Greenfield

--- In Electronics_101@yahoogroups.com, "ebiz_59" <chuckm@...> wrote:
>
> I have a camera system I want to convert to battery operation, and have both
gel cell and marine lead acid 12 volt batteries available. The camera requires
12 V +/- 1 v at 300 milliamps and the DVR requires 5 V at up to an amp. I'm
rookie, so am wondering if I should bother with like an LM7812 on the camera, or
should I just feed battery voltage directly to it? And is there something better
than the LM7805, since I'm going to want to use the least electricity as
possible, thus not waste elec on the heat generation of dropping 7 volts at an
amp. Thanks, Chuck
>