Bias Point Simulation Current

Discussion in 'Homework Help' started by J_Rod, Oct 9, 2015.

  1. J_Rod

    Thread Starter Member

    Nov 4, 2014
    109
    6
    Hello,
    I ran a bias point simulation in PSPICE of the circuit. I am wondering what the prefix capital K is. Is that kilo? That seems too large of a current.
    pspice transistor K.png
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    I do not know PSPICE.
    Lots of members over here use LTspice.
    I also see that the base-emittor voltage is very high (1.215V).
    Normaly I would expect 0.6 - 0.7 Volts.

    Bertus
     
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  3. WBahn

    Moderator

    Mar 31, 2012
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    Look at where all the current is going.

    The problem (and you will have this with any simulator based on PSpice, which includes LT Spice) is that the simulator input files are case-insensitive. Hence your 1M base resistor is 1 mΩ, not 1 MΩ. The prefix for mega is meg (or MEG).

    So how might you have spotted this?

    Whenever you get wonky results, walk through things and see where the wonkiness is focused.

    Consider the voltage across the base resistor is (20 V - 1.215 V) = 18.785 V. You have 18.79 kA flowing through it. So using those you get a base resistance of 1 mΩ.
     
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  4. J_Rod

    Thread Starter Member

    Nov 4, 2014
    109
    6
    Ah, that makes sense. I'll have to rerun the simulation in LTSPICE.
     
  5. WBahn

    Moderator

    Mar 31, 2012
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    Why do you have to rerun it in LTSPICE? Just correct the error (which will be the same error in LTSPICE) and rerun it in PSPICE.
     
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  6. J_Rod

    Thread Starter Member

    Nov 4, 2014
    109
    6
    That's a good point. I'll remember to type 1000000 or 1meg. But they lock the lab, which has the only computers with the licenses for PSPICE, and I had to quickly run the simulation since the lab took the full time.
     
  7. WBahn

    Moderator

    Mar 31, 2012
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    I'd recommend using 1meg as it is awfully easy to be off by one zero in 1000000 and not catch it.
     
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  8. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    You can always use scientific notation ...
     
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