Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!yale!mintaka!streeter
From: streeter@theory.lcs.mit.edu (Kenneth B. Streeter)
Newsgroups: sci.electronics
Subject: 12V to 5V DC conversion (for TTL logic in car) wanted
Message-ID: <1990Jul12.024412.122@mintaka.lcs.mit.edu>
Date: 12 Jul 90 02:44:12 GMT
Sender: daemon@mintaka.lcs.mit.edu (Lucifer Maleficius)
Reply-To: streeter@im.lcs.mit.edu (Kenneth B. Streeter)
Distribution: na
Organization: Laboratory for Computer Science, MIT
Lines: 28


Some of you may recall a previous query concerning building an
electronic odometer for my car.  (The application is TSD rallying.)
Well, I've pursued a number of ideas, and still haven't really reached
a decision.  However, I am having power supply difficulties with one
of my test circuits.

In order to supply the 5V needed to drive the circuits, I am using a
pair of 7805 regulators, using the car's 12V power as a supply.  I
have each regulator driving about half a dozen CMOS chips (uv erasable
PALs, mainly) and five or six hexadecimal LEDS.  (The regulators
aren't in parallel, they're each driving separate sets of chips.)
However, I seem to be having power supply difficulties.  The
regulators can just barely handle the current requirements, it seems.
They get REAL hot (even with heat sinks) and can barely muster 4
volts.  This makes the circuit VERY flakey.

Driving the entire circuit from an external 5-volt supply (bypassing
the regulators) indicates 1.26 amps of current being drawn.
Basically, I'd like a trouble-free, reliable 12V to 5V converter that
can push maybe 3 amps of current, and handle the switching transients
in the circuit.  Any suggestions?

--
Kenneth B. Streeter         | ARPA: streeter@im.lcs.mit.edu
MIT LCS, Room NE43-350      | UUCP: ...!uunet!im.lcs.mit.edu!streeter
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