AVR-Chat

At 07:31 PM 9/24/04 -0700, you wrote:
>any particular part number for the switching regulator, 5V at about 1A 
>from TI that can replace the 7805? thanks...

1 Amp with a 7-13V drop, not much wonder you are getting warm. That would 
be a 28 to 52 C rise from the heatsink to ambient for a good (4 C/W) TO-220 
heatsink. Add in junction to case rise of 35 to 65C and you would be 
running a heatsink of 50 to 70C (definitely hot to the touch) and a 
junction temp of 85 to 135C.  Nationals data sheet indicates a maximum 
junction temperature of 125C so you would clearly be in danger of shutdown 
at the higher voltage inputs.

As far as a switching replacement you might take a look at these

http://focus.ti.com/lit/ds/symlink/pt78st105.pdf

I've not used them so I can't say how good they are.  You would need to 
check their thermal performance but a quick glance looks good.  I'm not 
100% sure they fit in a to-220 outline but if I am remembering correctly 
the rep that pointed them out to me once upon a time said they either did 
or were close.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III