On Sat, 24 Aug 2002, Jinx wrote:

>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 ? 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

There is no 'best'. Use a thyristor with a divider (can contain a zener to
increase trip point precision), and a fuse. There are fast crowbars that
use mosfets to short the power lines. Wire the led in parallel with the
fuse, with a suitable resistor. TL431s can be used to drive the thyristor
with greater precision.

Peter

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