Path: utzoo!attcan!uunet!husc6!think!bloom-beacon!apple!rutgers!mailrus!purdue!decwrl!labrea!Portia!Jessica!paulf From: paulf@Jessica.stanford.edu (Paul Flaherty) Newsgroups: comp.sys.mac Subject: Re: crash and burn!!! Why no fuse? Message-ID: <3341@Portia.Stanford.EDU> Date: 17 Aug 88 05:14:51 GMT References: <561@calvin.EE.CORNELL.EDU> <27429@oliveb.olivetti.com> Sender: news@Portia.Stanford.EDU Reply-To: paulf@Jessica.stanford.edu (Paul Flaherty) Organization: The Three Packeteers Lines: 23 In article <27429@oliveb.olivetti.com> gnome@olivey.olivetti.com (Gary) writes: >Fuses are very good in preventing certain types of failures from >becoming fire hazards, but in general, they won't really protect >a hell of a lot in a computer system. The semiconductors will >blow much faster than a fuse. That's what crowbars are for. The firing time of a modern SCR is such that most overvoltage conditions can be clamped off before they damage the semiconductor stuff. A quick explaination for those who want to know: A crowbar circuit is designed to protect equipment from a failed power supply. It works by detecting an overvoltage condition and then shorting out the power supply; the short draws enough current to blow a fuse. The advantage of this technique is that an overvoltage condition lasts only for the trigger time of an SCR, which is small enough to protect most semicondutor circuitry. A power supply without a crowbar and fuse is a risky proposition. -=Paul Flaherty, N9FZX | "There is no distinctly American criminal class ->paulf@shasta.Stanford.EDU | except Congress." -- Mark Twain