14 V eh? Sounds like automotive mains. A nasty environ - I lost LM555's when powered directly off automotive mains YEARS ago - on one of my first projects! Solution was to add a real - sorry, an "RF" term there - add a series resistor along with a shunt electrolytic cap - any 'spikes' are met by (dropped across) the R (chosen based on some maths) against the influence of the electrolytic cap ... RF Jim "Our ability to manufacture fraud has exceeded our ability to detect it." - Al Pacino as Viktor Taransky in the movie 'Simone' ----- Original Message ----- From: "Jinx" To: Sent: Friday, August 23, 2002 5:32 PM Subject: [EE]: Crowbar protection > 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 > > Generally I'd want this to protect a circuit that needs 5V @ > 100mA or less, which is probably not enough to blow a > common fuse, but should be sinkable by a modest semi. > Failure indication by LED would be nice > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body