BJT project - question

Discussion in 'Homework Help' started by ibm123, May 13, 2009.

  1. ibm123

    Thread Starter Member

    May 13, 2009
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    i made a project with BJT NPN
    now for some reason the Ic and Ib are ok and positive but the Emitter current is ok but negative
    anyone can explain me why is it negative and how can i fix it...
     
    Last edited: May 13, 2009
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    But you can't see the entire schematic!
     
  4. ibm123

    Thread Starter Member

    May 13, 2009
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    ok.. hope now its okay
     
  5. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Is this your first OrCAD simulation? If not, have you seen this problem before?

    If there are inbuilt example circuits, do they show a similar behavior?

    Perhaps there is a simulation option setting that needs attention?

    I've never used OrCAD so I've no obvious answers.

    Have you checked the OrCAD community forums web site?
     
  6. mauro.laurenti

    Active Member

    May 8, 2009
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    it's normal the behavior you found.

    Just change the transistor with a node.
    ...if all the currents where positive where the electrons can get out?

    ...what ever get inside a node need to get out...
    Something will be positive and something most be negative (independently of what positive and negative means)

    The water from the sink that flow in the hose will get out from the other side...

    Ciao,

    Mauro
     
  7. ibm123

    Thread Starter Member

    May 13, 2009
    17
    0
    its not my first simulation
    it is an inbuilt example circuits but the behavior is not similar..
    actually the current in the Emitter need to go down.
    but the spice shows it as - i want it to show it with a + sign

    the base and collector current need to get inside the transistor and go out from the emitter

    anyone ?
     
  8. mauro.laurenti

    Active Member

    May 8, 2009
    68
    0
    Check the node below the transistor...and the output current that goes down to the mirror...it's positive...which is what you want.

    I would assume that the current sign is related to the node...

    For the current is the sum that should bother you and not the single sign...


    Ciao,

    Mauro
     
  9. mauro.laurenti

    Active Member

    May 8, 2009
    68
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    ...I want to tell you more...

    For instance with LTspice if you turn the resistor the current within it changes sign...which is strange...

    ...but the sum is always correct...

    Ciao,

    Mauro
     
  10. ibm123

    Thread Starter Member

    May 13, 2009
    17
    0
    its only a sign..
    but still annoying :)
    thanks
     
  11. mauro.laurenti

    Active Member

    May 8, 2009
    68
    0
    ...... ...:)
     
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