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Vendor's Description: 

The KA378R05 is a low-dropout voltage regulator from Fairchild Semiconductors. From the page, "Dropout voltage of KA378R05 is below 0.5V in full rated current(3A)". It does have a 4-pin layout, the fourth pin is "Disable". Just tie that pin to your supply line and it'll work fine.

Available at Mouser for $1.58, probably elsewhere too. I got mine as free samples from Fairchild, so you may find some that way too.



2009 July 01, added quickie schematic

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I'm not going to update the actual post, because I don't want this to bump onto the front page again ;)

I replaced the schematic with a (hopefully) better version. If it's hard to see, right-click and "View Image" (or whatever your browser calls it), should be a bit clearer that way.

I didn't find an Eagle library with this part in it (didn't look very hard either) so I tried making one. That's why the part looks... off. I'll likely update again if/when I learn more about making custom parts and footprints and stuff.

I assumed as much. I guess this cap set-up is sorta "standard" with any kind of power system....
Input/output capacitors help absorb spikes and in the process slow down the rate at which input and output voltages fluctuate. This prevents the regulator from overcompensating for sudden changes and provides stability.
Thanks Bunches for this post, this is exactly the part I need. However, in your schematic, you have no polarized caps... Did you just miss the + sign when you drew it up?

Oops. Ya, I missed that part. That's what I get for quickie diagrams... haha. I'll draw a proper one with Eagle later on.

The two 100uF would be polarized. The datasheed says 47uF or greater. 

Looks very useful