Quote:
how much power (in Amps) would a 5V 3A voltage regulator require? I Can find everything else on the datasheets except that...


If it's a linear power regulator, then 3A -- it just drops Vsupply (12-14.5V in a car, typically) minus Vout (5V in this case) volts across itself, generating (Vsupply-Vout)*Iout watts of heat... (Iout not neccessarily the max (3A) current, but what is actually drawn).

A switching regulator would require at least 15W of input power (5V*3A) if the load actually draws 3A, less if the load draws less. Assuming a supply voltage of 12V that means 15W/12V=1.25A. That is the ideal case, ie if there were no losses. In the real world you'd have a somewhat higher current due to the losses.

Not sure what sort of efficiency numbers you get today for a) cheap or b) good switching supplies, so I can't say how much more current to expect, but a guess is that it's less than 20% extra...

/Michael