Thanks for the links Richard. hadn't seen glitchbuster before.... I've continued on (bumping Vin up to 16V) and I'm getting 4.89V from my zener, hopefully close enough.... Thanks for the help all.... ----- Original Message ---- From: Spehro Pefhany To: Microcontroller discussion list - Public. Sent: Wednesday, December 26, 2007 10:58:31 PM Subject: Re: [PIC] El Cheapo zener tolerance question At 03:53 PM 12/26/2007, you wrote: >Hi, I'm constructing El Cheapo and having some problems. When I >check the voltage across the 5.1V zener I get 4.87Volts. this threw >me initally but I noticed a 5% tolerance on the packaging so its >within the 5% tolerance. Is this sufficient or have I bought an >incorrect component? The El Cheapo construction/debug info states >that I 'must' be getting 5.1 volts from the zener? > >Thanks > >Richard Aside from the tolerance you must consider that the specified voltage plus-minus a tolerance is at a specific reverse current (usually quite high-- like 20mA) and particularly lower voltage zeners (which have soft "knees") will have rather less reverse drop than the marked voltage. Although this does not sound unexpected to me, that doesn't mean that it will work as intended, but that's a circuit design issue not a component issue. >Best regards, Spehro Pefhany --"it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist