Okay, you used the word "clean" with respect to automotive power, so you'=
ll=20
have to allow me a half hour to get over my laughter :-)

Seriously though, most everything I do with PICs is in automobiles, and t=
ake=20
my word for it, that the ~12V in a vehicle is one of the worst environmen=
ts=20
from an electrical/power standpoint.  There are so many generators of=20
significant electrical noise, that you're committing circuit suicide if y=
ou=20
don't protect the circuit.

First, 11V to 14V is fairly common, but I like to conservatively assume i=
t's=20
10V to 15V.  Then, there are positive surges and spikes, negative spikes,=
 and=20
tons of noise.  So at the bare minimum, use a forward-biased rectifier di=
ode=20
to protect against reverse current, add a TVS or zener to protect against=
=20
positive spikes, filter that, then regulate the usual way.  That's if it'=
s a=20
PIC or similar circuit.  If you need a solid clean 12V for a stereo (I ca=
n't=20
figure out if you mean that the power that is usually supplied to the ste=
rep,=20
or if you intend to use if for a stereo), then you'll need a DC-DC conver=
ter=20
(flyback, sepic, etc), but I'm not sure if this is your intention.

Cheers,
-Neil.



On Friday 22 August 2003 20:36, NaB25J@AOL.COM scribbled:
> Hey, everyone
>
> How clean of a source is the 12v stereo power supplied by a car? I've
> noticed it can vary from (in my car) 11.5v off the battery to almost 14=
v
> when the engine is running. I'm thinking that it's not a very well
> regulated source. So how likely is it that spikes and noise can make th=
eir
> way into the circuit being powered? The vehicle in question is a 1991 G=
eo
> Prizm (basically a Toyota Corolla of the same era).
>
> I ask because I'm not sure what kind of protection might be needed in a
> circuit to be powered by such a source. If it's a significant problem, =
what
> can be done about it?
>
>
> Thanks, and happy Friday
>
> -Tony

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