drawing transistor saturation Vbe/Ic curve

Discussion in 'General Electronics Chat' started by gumof, Jul 22, 2014.

  1. gumof

    Thread Starter New Member

    Jul 22, 2014
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    i got unknown transistor(couple of),
    and i need to create spice model of it
    -for simulation purposes
    how to draw characteristic like that:
    [​IMG]

    how circuit would look like to measure it ?
    "..the ratio Ic/Ib = 10" -what that means in practice ??
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Creating transistor Spice models from characteristic curves is not easy. The easiest is to find a comparable transistor that has a model.

    Ic/Ib = 10 just means the the curve is measured with a base current always equal to 1/10th of the collector current (i.e. the transistor is saturated).

    Below is such a plot in LTspice. It doesn't exactly match your posted plot so there obviously is some difference between the LTspice model and the transistor characteristics in the data sheet.

    Sat Plot.gif
     
    Last edited: Jul 22, 2014
  3. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Ic/Ib=10
    Ic=10*Ib
    When:
    Ib=1 mA, Ic=10 mA
    Ib=2 mA, Ic=20 mA
    Ib=3 mA, Ic=30 mA
    etc.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    See the sim I added in my previous post.
     
  5. gumof

    Thread Starter New Member

    Jul 22, 2014
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    and that means...
    ...simplifying if i place Rc = 1K, Rb=10K || Rc= 10K, Rb=100K
    will be good enough ??
    circuit like that:
    [​IMG]
    to plot characteristic like in post#1
    or it has to be done with current sources like your attach. ??:
    [​IMG]
     
  6. crutschow

    Expert

    Mar 14, 2008
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    It's better to use current sources to keep the base current exactly 1/10th of the collector current. Note that you have to step both sources simultaneously, not just one.

    Why do you want to use voltage sources? Doesn't your simulator have a current source?
     
  7. gumof

    Thread Starter New Member

    Jul 22, 2014
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    all right, thanks guys.
    _obvious that i have to keep ratio :)

    have you got any suggestion which current sources to build (or IC ?)
    for that purpose (simple, good enough) ??

    How about any company/paid service/anybody can grab/capture
    transistor characteristic curves by curve tracer device (like B1505A)
    or any other solution that provides reliable/accurate measurement ??
     
  8. crutschow

    Expert

    Mar 14, 2008
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    Certainly if you have access to a curve-tracer, that should do the measurements.

    Otherwise you could simulate a current source with a couple power supplies and two series resistors, one to the transistor base and one to the collector. Add a ammeter in series with each resistor to monitor the currents.
     
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