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Thread: Transistor question

  1. #1
    Old Timer
    Join Date
    Sep 2011
    Pace, FL

    Transistor question

    I was reading on this site Troubleshooting & Repair Guide
    Section 5.1

    In the most general of terms, with any bipolar transistor (FETs and MOSFETs are completely different!), there should be about 600-700mV measured between the emitter and base

    Am I correct in understanding one probe on emitter and one on base?



  2. #2
    g1 is offline
    don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Canada, somewhere north of Fargo
    Yes that is correct. And the polarity of 'which probe where' will be determined by whether it is NPN or PNP.
    Reversed will measure 'OL' or equivalent, forward will measure any where from mid 400's to mid 700's in my experience.
    Certified Dotard

  3. #3
    Senior Member
    Join Date
    Jan 2014
    I have an old 'note' that I saved that Fahey said a while back. I'm still no transistor master so I save it for reference. Hope it helps

    Universal "expected voltage rules"
    a) a base must be some 600/700mV more positive than the emitter for NPN, negative in PNP.
    b) a collector must be at least 2V more positive than the emitter for NPN, negative in PNP
    that's it

  4. #4
    Old Timer olddawg's Avatar
    Join Date
    Dec 2007
    Carlsbad, CA and Kona, HI
    .6-.7v for a foreword biased emitter/base junction for a SILICON transistor.

    .3-.4v for a foreword biased emitter/base junction for a GERMAINIUM transistor.

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