AVR-Chat

On Tue, Feb 10, 2009 at 1:44 PM, Steven Hodge <stevehodge@speakeasy.net> wrote:
> Yeah, I stupidly blundered into that one on the capacitor, all right.   But,
> I'll bite.   I don't have any diodes.   The power source is not an AC power
> supply but a 12 VDC battery (a large 700 amp-hr boat system) and I don't
> bother with reverse polarity protection (I prefer being careful to suffering
> the voltage drop).  It's just battery to fuse to switch to regulator, with
> cap on the input to regulator.    Would a current-limiting resistor in
> series with the cap be a good idea to help protect the switch?   Steve

It would help.

Running "naked" on a vehicular bus has its own set of problems.
Alternator load dump transient, etc can kill you really easily.
They do make regulators designed to cope with that, check for
"automotive" types.

Another fun failure mode that most three-terminal regs have, is when
the input is shorted to ground.
If the output has any significant capacitance, this can kill the reg.
It's documented in the older motorola sheets on the 340 series and
nationals on the 78XX series, but most three terminal regs have this
weakness.  A diode connected from input to output, such that it is
normally reverse-biased, solves the problem.