>Thomas C. Sefranek wrote:
>>Richard Sloan wrote:
>
>>> Yes heat is an issue that needs to be addresses also as a 7805 was attempted
>>> and man does it get HOT!
>>
>>Ohms law:  12V - 5V = 7 volts at 1 amp, = 7 WATTS of heat.
>>You can waste some of that heat in a 5 ohm resistor (5-10 watts) in series
with
>>the +12
>>to the 7805.
>>
>
>Not the most elegant or cheapest solution, but you might also
>consider small-V 5W zeners instead of a series R. I have one
>item where I do this, but is Vz = 4.3v @ .3A, so only about
>1.5W.
>

No matter how you do it, if you aren't switching then you are
dissipating it.  And the combination of resistors or zeners
or pass transistors all add up to that 7 watts of heat and
you will have to get rid of it somehow.  And heat sinks
aren't free, either.

And a mobile unit that's too hot to touch is rather embarrassing
(don't ask how I know this:)

Barry

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.