as a comment to my last post there are adjustable 'buck' mode switchers available from ebay for <$2.00.
I bought 3 of them at 1.89 ea and at 98% efficiency a 5 volt 100 ma load would dissipate 2% of .5 W (from my last post) so...
Ploss = (100-98=02%) .02 x .5 = 10 mw as heat. The switchers are capable of a 2 amp load continuously...
according to the printed specifications, I don't know as I would draw more than 1A but they would make
great supplies for peripheral assemblies. Just to make SURE that all grounds are common.
Doc.