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From: gsteckel@vergil.East.Sun.COM (Geoff Steckel - Sun BOS Hardware CONTRACTOR)
Newsgroups: sci.electronics
Subject: Re: WAIT! - Re: 12 to 9 volts dc (kinda long)
Summary: discman frying
Keywords: safety
Message-ID: <4582@eastapps.East.Sun.COM>
Date: 1 Mar 91 00:21:16 GMT
References: <1991Feb10.220719.17078@cbnewsl.att.com> <erk.1356@americ.UUCP> <1991Feb26.235009.1389@cbnewsj.att.com> <5825@optilink.UUCP>
Sender: news@East.Sun.COM
Reply-To: gsteckel@east.sun.com (Geoff Steckel - Sun BOS Hardware CONTRACTOR)
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Organization: Omnivore Technology, Newton, Mass. (617)969-3448
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The whole thread of `how to run X from a automobile battery should be in
a FAQ file.

The LM317 is a good chip for this sort of linear stepdown application.

BUT:
  the automotive alternator/battery/voltage regulator combination can produce
  violent transients, AND
  most power semiconductor devices fail shorted under these conditions

Do you really want to send the 140 V load dump or the 1500 V spike through
your homebuilt regulator into your $200+ portable stereo?  I didn't think so.
(:-)  The monolithic voltage regulator can only do so much.

You want at least a series fuse, a zener/MOV overvoltage protector, and some
RFI/EMI protection - the little microprocessor in a Discman gets confused easily.
Reverse voltage protection is nice, too.  Only about $2 for parts, too.

Could someone who has them accessable (= not under 1000Kg junk in attic) post
references to application notes, etc., describing the automotive electrical
environment?  I will as soon as I find mine, but that might not be soon...

	geoff steckel (gwes@wjh12.harvard.EDU)
			(...!husc6!wjh12!omnivore!gws)
Disclaimer: I am not affiliated with Sun Microsystems, despite the From: line.
This posting is entirely the author's responsibility.