What is a complementary bipolar transistor?

Discussion in 'General Electronics Chat' started by annahughes, May 25, 2016.

  1. annahughes

    Thread Starter New Member

    Apr 16, 2016
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    Pretty much what the question says. Is it just a fancy name for any npn and pnp bjt?
     
  2. SLK001

    Well-Known Member

    Nov 29, 2011
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    They are two transistors that have close to identical properties, except for being opposite in polarity.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    3,048
    Ditto, it just means that the transistor is a close match to one of the opposite polarity. Probably as much a marketing tool as anything else, to sell two transistors instead of risking that the designer looks for a complementary one from another supplier.
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    In some designs it is useful to have NPN and PNP transistors that are well matched to each other with regard to a number of the parameters. Using them allows the designer to squeeze some of the cost and complexity out of a design while maintaining adequate performance. The designer could always search data sheets to find a suitably matched transistor, but having the manufacture offer one up usually saves a bunch of time and effort -- and the designer's time and effort also represent costs to the project.
     
  5. crutschow

    Expert

    Mar 14, 2008
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    A typical example of where complementary matched transistors might be used is in a linear push-pull power output stage.
     
  6. SLK001

    Well-Known Member

    Nov 29, 2011
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    It used to be that manufacturers would put the two devices on the same substrate. That way, thermal effects would occur equally on both transistors, thus minimizing the need for separate compensation circuits. I don't know if this is done any more.
     
  7. #12

    Expert

    Nov 30, 2010
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    Not at the TO-220 or TO-3 level. Too much heat to get rid of. You can still get them in TO-5 size or plastic DIP.
     
  8. SLK001

    Well-Known Member

    Nov 29, 2011
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    There aren't many complementary pairs at that level.
     
  9. Lestraveled

    Well-Known Member

    May 19, 2014
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    Amplifiers that use complementary TRANSISTOR pairs are long gone. Sure you can find some old Sansui or Phase Linear amps that used them, but they are going on 40 plus years old.
     
  10. WBahn

    Moderator

    Mar 31, 2012
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    While I've never done much with complementary pairs of discrete transistors, I believe the TO-3 cased 2N3055 has a complementary PNP in the MJ2955. I think (but don't know) that this is the same as the 2N2955.
     
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