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From: wdp@dukee.egr.duke.edu (Dev Palmer)
Newsgroups: sci.electronics
Subject: 12V to 5V conversion
Message-ID: <987@cameron.egr.duke.edu>
Date: 12 Jul 90 13:44:50 GMT
Sender: news@egr.duke.edu
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Date: 12 Jul 90 

Mr. Streeter:

Since you are dropping 7 V across the regulator, you are generating quite a 
bit of heat and the regulators may shut down or at least begin to shut down.
I had a circuit where the regulator was pulsing on and off.  It looked like 
low voltage to a multimeter, but an oscilloscope revealed the thermal cycling.

If you really want 3.00 A (giving 15.00 W), you really should heed collie's 
suggestion to use a TO-3 package, but you should use the LM350K adjusted to
5 V and mounted on a BIG heat sink (heck, mount it on the firewall!).  That
should give you all the juice you need.  Buy it from DIGI-KEY (1-800-DIGI-KEY,
part number LM350K $5.56) or your favorite supplier.

Also, check National Semiconductor's Voltage Regulator Handbook.  The 1982 
edition has a section called Automotive Applications which should be very 
informative.

Good Luck!

Dev Palmer
Electrical Engineering
Duke University (not DIGI-KEY or National Semiconductor)
Durham, NC  27707
(919) 660-5282
wdp@dukee.egr.duke.edu