Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

BJT common emitter collector to emitter reverse bias confusion

  1. Sep 15, 2009 #1
    Iam sorry if it is a very basic question but iam unable to understand this

    if u take a common emitter configuration of npn transistor the emitter is common to both the input and output terminals and to operate in the active region
    1. the emitter to base should be forward biased i.e n and p should be forward biased this is fine,
    2. also the emitter to the collector should be reverse biased that is n and n regions should be reverse biased but how can u reverse bias this.

    it is very confusing could somebody clarify on this.

    Thanks in advance,
  2. jcsd
  3. Sep 15, 2009 #2


    User Avatar
    Science Advisor

    In an NPN transistor, the base is an anode for two diodes and the emitter and collector are cathodes.
    So, if the base is more positive than one of the cathodes, that diode will be forward biassed.

    This is clearly the case with the base emitter junction.

    With the base collector junction, the collector is normally at a higher positive potential than the base, so it reverse biasses this diode.
  4. Sep 15, 2009 #3
    Thankyou i understood it now.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook