> A couple of days ago I had a 7805 regulator fail and stick
> 14V up a circuit, taking out an F877 and an LCD. To quote
> my old French boss " I em 'ow you say ? urn'appy "
>
> What can I use as a shunt circuit to stop this 'appening
> again ?

You should first ask yourself whether it's really worth it.  This kind of
failure is very rare.  The cost of the protection parts will likely be way
more than the average cost of the damaged circuit.  Of course, there could
be other costs if the circuit fails that can make the protection worth it.
Another justification might be for bench use where failures and abuse are
more likely.

> I've seen various semis used (SCR, FET, BJT)
> with dividers, zeners etc but know that this list always
> comes up trumps. I've tried the rest, now I want to try the
> best

A zener, power transistor, and a resistor work pretty well to make a "high
power" zener equivalent.  The result is less accurate than the original
zener, but just fine for shunt protection.  Of course the whole setup needs
to be able to sink enough current drag the supply low enough or to blow a
fuse.


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