Differences between NPN and PNP transistors.

Discussion in 'General Electronics Chat' started by RichardO, Nov 15, 2013.

  1. RichardO

    Thread Starter Well-Known Member

    May 4, 2013
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    I am curious about the subtle differences between PNP and NPN bipolar junction transistors.

    I have read that the Vbe of a PNP is greater than that of an NPN at the same collector current? Why?

    It seems that the transition frequencies of NPN are, in general, greater than PNP's. Is this observation correct? Why or why not?

    Are there any other small differences between PNP and NPN transistors I should be aware of?

    Thanks in advance for any insight on these questions.
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    The main difference is in the circuit configuration. You would not use a PNP transistor in a circuit that calls for an NPN and vice versa.
     
  3. Papabravo

    Expert

    Feb 24, 2006
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    It is not a subtle difference, but they are made of different kinds of raw material.

    N-type material is silicon doped with donor impurities that provide extra electrons.
    P-type material is silicon doped with accceptor impurities that can accept extra electrons, because the have 'holes'.

    http://en.wikipedia.org/wiki/Extrinsic_semiconductor

    In either case the 'magic' is that small currents at the base control large currents at the collector/emitter. It is called amplification and it is not the same thing as a free lunch.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    To the casual observer, it appears that for a given cost, the N transistor will often have superior specs and just generally be "better". So I think most designers would choose an N type, all other things equal.

    Obviously there are many applications that call for a P type and any deficiency versus an N type is small. N wins in a tie, but otherwise you choose the one that makes sense for the application.
     
  5. MrChips

    Moderator

    Oct 2, 2009
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    I thought a tie is a tie.;)
     
  6. vpoko

    Active Member

    Jan 5, 2012
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    Yesterday, Albion, Alaska elected a mayor by coin toss after the election resulted in a tie. So sometimes, someone wins a tie.
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    In Blackjack, ties go to the dealer. It's good ta-be-da dealer.:D
     
  8. crutschow

    Expert

    Mar 14, 2008
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    In NPN's the carriers are electrons which has higher mobility than the hole carriers for PNP's. This makes the gain and frequency response of an NPN higher than a PNP for the same physical transistor layout. Thus NPN's are usually preferred unless the complimentary operation of a PNP is required in the circuit design.
     
  9. tshuck

    Well-Known Member

    Oct 18, 2012
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  10. WBahn

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  11. tshuck

    Well-Known Member

    Oct 18, 2012
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    They will be the majority carrier in the collector and emitter regions, but not in the base region.

    I am being pedantic since the OP is asking for the differences between the two types of BJTs, which require a correct understanding of what is happening where.

    Of course, one could just say that holes don't exist as anything but the absence of an electron, which would mean that the electron is, indeed the charge carrier at all points, but I assume this is from an academic point of view.
     
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