Solved ignition noise problem...thanks all!

[garfield at pilgrimhouse.com]

On Thu, 14 May 1998 17:48:12 -0700, Sandy <sganz at wgn.net> wrote:

>Great, the LM2935 is slated for death, it is not recommend for new designs,
>but the problem is that the Switch/Reset lead was acting as an antenna and
>shutting down or glitching the main power for some reason. Get the 3
>terminal LM2940-5, it is the automotive equiv. of the 7805 and has better
>specs. like the LM2935. Keep us posted.

Gee, I hope you're right Sandy, but I gotta tell ya I thot about this a
couple times today, it just popping into me brain, I strongly suspect
that the 2935 wasn't failing or being reset by lead noise, but rather
was doing what it's supposed to do, which is shut down and pull down the
reset line, IF it sees one of the several fault conditions it's got
internal protection against. For example, as you well know, you don't
carefully bypass and protect an IGN or INJ driver, say, and it easily
will put what looks like a load-dump phenom to the 2935 on the +12V. If
that puppy sees ANY transient on the supply lines above say 60V, which
it's easy to do with stray IGN or INJ driver noise, it HAS to think the
ALT has gone berserk, and WILL shut down and yank on the reset. It's
claim to fame is doin just that. I bet the 7805 worked better cuz it
just didn't notice the fast "incoming", and the transient probably got
smoothed by later filtering. If this is the case, the 2935's behavior
might better be considered a warning than a failure.

Finally, not to be anal or anything (who me? B), but the 2935 is/was an
excellent device, and is only being end-of-life'd cuz it got so popular
that it was replaced by a cost-reduced family of many diff. voltage
setpoint fixed regulators, with a tad better output current, etc. But it
includes the same set of protection features, and ALSO will shutdown if
dumped on. We use the 2935s in some aviation stuff and wouldn't leave
ground without it. We're switching over to the 2940-5s cuz they're newer
and cheaper, but they're still same ole good stuff as before. The 2940's
are especially nice cuz they are also available in mil/aero rated
versions for much broader temp range, a nice thing if your butt or even
just your winning an important race might depend on it.

Just me dos centavos, amigos.

Gar

>At 11:56 AM 5/14/98 -0700, you wrote:
>>Fellow EFI'rs
>>	Well I did it!  I finally got around all the noise.  For starters the
>>system wasn't in a box...fixed that.  The real problem seemed to be the
>>voltage regulator I was using (LM2935).  It was resetting the CPU every
>>time the ignition fired.  Fixed that with a 7805.

P.S. For those that might appreciate the "automotive" style of this
voltage regulator, here's it's "stuff":
	low/cold bat protection (very small hdroom required for regulation)
	reverse bat connection protection
	load dump/field interruption protection
	negative transient protection
	"double battery" (bad hair day during jump starting) protection
and some I probably forgot. It was made for us car bozos. Heh.