🚀 go-pugleaf

In article <4582@eastapps.East.Sun.COM> gsteckel@east.sun.com (Geoff Steckel - Sun BOS Hardware CONTRACTOR) writes:
>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.

I think this is getting a bit silly.  First of all, the adapter that
Sony sells doesn't have that much stuff in it - probably a simple
regulator, maybe a filter cap for minor de-spiking, reverse polarity
protection (diode), and a fuse.  That's it.  There is no RFI/EMI protection,
no MOV, _maybe_ a zener for OV.  How much do you think they're going to give
you in a $20 adapter (maybe $5 worth of parts)?

The easiest way I can think of is also the simplest (KISS).  Take a
78H09 regulator, mount it to something (a very small project box),
put a back-biased diode across the 12v input, and a fuse in-line with
the output.  Total cost: $4.00 + cost of cigarette lighter plug.

EMI/RFI - forget it.  An MOV is your only hope of protecting the unit
from high-voltage spikes, but again, I've never seen the need.  Look
at all of the car electronics that don't use them - is everyone else
wrong?  I don't think so.  It's overkill, IMHO.

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 Jeff DePolo  N3HBZ             Twisted Pair: (215) 386-7199                  
 depolo@eniac.seas.upenn.edu    RF: 146.685- 442.70+ 144.455s (Philadelphia)  
 University of Pennsylvania     Carrier Pigeon: 420 S. 42nd St. Phila PA 19104