Thermal runway

Discussion in 'Homework Help' started by zamansabbir, Jun 1, 2008.

  1. zamansabbir

    Thread Starter Member

    May 27, 2008
    15
    0
    Hi
    i got question in my previous year question paper that Define thermal runway in power amplifier section but could not able to get myself satisfied with the answer that got from my book.

    Will you please help to get a satisfactory answer.
    from Sabbir
     
  2. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    145
    What is the definition in your book?

    Dave
     
  3. circuitashes

    Active Member

    May 13, 2008
    37
    0
    Which specific part of the definition in your book are you not satisfied with? You need to give us that information so we can give you the needed help.
     
  4. zamansabbir

    Thread Starter Member

    May 27, 2008
    15
    0
    i just want the definition a proper one to understand the thermal runway .
    i just could not able to understand what my book said.
     
  5. circuitashes

    Active Member

    May 13, 2008
    37
    0
    If its a definition you want, you can check this link: http://en.wikipedia.org/wiki/Thermal_runaway
    However, i do not think what you need is a definition. Rather, what you need is a good understanding of the underlying principles described in the definition. You should do some reading on the ff:
    1. The effect a change in temperature has on the resistance of a semiconductor, and by extension on a P-N junction diode.
    2. The 'diode-equation' and how a variation in temp. affects the other parameters in that equation.
    3. The I-V characteristics of a P-N junction, and how a change in temp. affects the characteristics (specifically, how the slope is affected).

    This is one clue you can start with: For a semiconductor, an increase in temp. results in a decrease in resistance.
    For the diode eqn. check this link: http://www.allaboutcircuits.com/vol_3/chpt_3/1.html
    To see how thermal runaway can be dealt with, check this link: http://www.allaboutcircuits.com/vol_3/chpt_4/10.html
     
  6. mofokeng

    New Member

    May 14, 2008
    3
    0
    thermal runaway is an increase in collector current due to a small increase in base current of a bjt transistor which leads to a Rc heat up.To overcome thermal runaway we connect an emitter resistor in parallel to Rc.
     
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