Temperature compensation of BJT's information

Discussion in 'Electronics Resources' started by karmabobby, Jan 26, 2010.

  1. karmabobby

    Thread Starter Member

    Jan 20, 2009
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    Hi everyone, I am an E&EE undergrad currently undertaking quite an interesting project. I have to temperature compensate a circuit as the original 70's version had a reputation of being very sensitive to its operating conditions. Anyway I have been looking in books and so on and haven't found too much information on the temperature compensation of BJT's.

    I have found some information on the subject but most of my knowledge is very analytical and from books, and not of a practical perspective due to lectures etc. If anyone can point me to any information then it would be very much appreciated. Thanks!

    NB Sorry forgot to mention I am mainly concerned with differential pairs and darlington pairs.
     
    Last edited: Jan 26, 2010
  2. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    The main effect of temperature on a transistor is to change collector current by changing the base emitter voltage. This is compensated by biasing with a diode in parallel to the BE junction as with D1 in the sketch. The diode undergoes much the same change as the BE junction. So if the ambient temp rises causing a fall in Vbe the pd across the diode will also fall keeping the collector current sensibly constant.
    You should be able to look up the voltage temperature coefficient for a pn junction.
    I have chosen a long tail pair you can simulate to study the efffects of changing resistors etc.
    I will leave it as an exercise to apply to a darlington.
     
  3. karmabobby

    Thread Starter Member

    Jan 20, 2009
    13
    0
    Excellent, thank you for your informative reply! That along with the other method I have found should work nicely for my project, thanks!
     
  4. sgpkelvin

    New Member

    Oct 16, 2012
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    I came across some book with the diode connected the other way i.e the cathode to the base for temperature compensation. What is the difference between the two configuration? Thank you.
     
  5. studiot

    AAC Fanatic!

    Nov 9, 2007
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    513
    Perhaps a reference and a circuit diagram for discussion?
     
  6. sgpkelvin

    New Member

    Oct 16, 2012
    2
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    Sorry Studiot, I couldn't figure out how to attached an image here. I read this in
    http://books.google.com.sg/books?id=FPlJQ0iO7oQC&pg=PA193 under 6.13.1
    There he connect the diode the other way and I understand how the compensation worked from his explanation but your img confused me now. Do they both work the same? Thank you.
     
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