Most LED's fail open, but some fail shorted. For years, I have been using shorted LED's as infrared emitters.
Ed Price WB6WSN Chula Vista, CA USA -----Original Message----- From: John Woodgate [mailto:j...@jmwa.demon.co.uk] Sent: Friday, March 01, 2013 8:37 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] LED Chamber Lighting - drivers outside the chamber In message <of55b18620.c618ea44-on88257b21.00585dd6-88257b21.0059d...@selinc.com>, dated Fri, 1 Mar 2013, don_borow...@selinc.com writes: >John is right. You want to feed LEDs a constant current, and let them >drop whatever voltage they need. If I am not mistaken, LEDs have a >negative voltage temperature coefficient. With this being the case, >feeding a constant voltage will cause the current to increase as the >diodes warm up. The additional current will cause more heating. This >can lead to a "runaway" situation. I should have mentioned 'bad experience'. The runaway occurred only after everything appeared stable and was very sudden - too sudden to allow switch-off. Dead LEDs for sale cheap on ebay!!!! -- OOO - Own Opinions Only. See www.jmwa.demon.co.uk SHOCK HORROR! Dinosaur-like DNA found in chicken and turkey meals John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
