The FET crowbar is a good solution and it works well. It is also very fast and unlike a thyristor it will not latch on (unless you make it). You have to provide gate voltage from somewhere (storage capacitor) while the FET is conducting since it will short the bus. Peter -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body