At 04:22 PM 6/1/2005 +0200, you wrote:
> > A series fuse say 1/4 amp fast acting followed by a 1N400x
> > reverse biased diode would seem to be the simplest solution.
> > The fuse should be heavy enough for max peak load, but still
> > blow in a reverse power situation.
>
>Yeah, that is one solution, but it is not self-repairing, which I would
>prefer. I dunno, the fuse might not even be fast enough to prevent the
>diode from exploding.

You could use a 1N5403 and it would be more rugged-- would probably work,
until they replace the fuse with a 30A type anyway.

>Wouter van Ooijen

Perhaps the series inverted MOSFET method, but I'd suggest a TVS across the
power supply in case it gets suddenly disconnected, depending on how
much capacitance you have there already. You can calculate the energy
stored in the inductance and the resulting voltage change with a given
capacitance, once you know the inductance and the current (energy = L*i^2/2,
energy = C*v*2/2.

The problem with fuses (and resettable "polyfuses" on an automotive battery
is that the fault current is rather high (the latter are typically limited
to protecting circuits with something like 40A maximum fault current).


Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com




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