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Setting Vbe in PSPICE?

Discussion in 'Electronic Design' started by Emily, Oct 25, 2006.

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  1. Emily

    Emily Guest


    I would like to set Vbe to 0.8V to a transistor in PSPICE. How should I
    set it? I click on the transistor, I click on Edit->Model, then Edit
    Instance Model(Text), then what? Which parameter to set Vbe?

  2. Tom Bruhns

    Tom Bruhns Guest

    Vbe in a working circuit is determined by many things, not just a
    single parameter in the Spice bjt model. Try varying VJE to get the
    performance you expect. (I'm assuming that Spice2 uses the same
    parameter name as Spice3 here, but if not, change the "B-E built-in
    potential," or switch over to a Spice3 based simulator such as the free
    and very nice LTSpice.)

  3. Guest

    In the old versions of Pspice, it would be VJE or PE (either will work).
  4. Jim Thompson

    Jim Thompson Guest

    "whit3rd" AND Tom Bruhns.... shame be upon thou...

    VJE/PE sets the curvature of junction CAPACITANCE

    IS (primarily) sets VBE versus current.

    ...Jim Thompson
  5. Genome

    Genome Guest

    Oooooh that's interesting. Does it apply to deeodds as well?

    Hold that thought I'll have a look....

  6. Jim Thompson

    Jim Thompson Guest

    Yeth ;-)

    ...Jim Thompson
  7. lemonjuice

    lemonjuice Guest

    You can set Vbe outside the .MODEL statement
    A simple example ...
    Vbe 1 0 0.8V
    Q 1 1 0 QNPN
    Vc 2 0 1V
    ..MODEL QNPN NPN(Is=10fA Ikf=150mA Isc=10fA Bf=150
    + Br=3 Rb=1ohm Rc=1ohm Va=30V Cjc=10pF Cje=15pF)

  8. Jim Thompson

    Jim Thompson Guest

    Sheeeeesh! etc, etc, etc... ;-)

    Vbe, as "lemonjuice" has shown in his/her netlist is a VOLTAGE
    SOURCE... thus _forcing_ that potential.

    The OP, if I understand her correctly, wishes to have a device with
    Vbe = 0.8V at some defined current level.

    If she wants Vbe = 0.8V at Ie = 1mA, then she should set IS =

    IS = Ie*(e^(-q*Vbe/(k*T)))

    ...Jim Thompson
  9. Tom Bruhns

    Tom Bruhns Guest

    (Slaps forehead...) (Blush) yes indeed. Thanks, Jim. However, ISE,
    RB and RE also have an effect, the resistances especially noticable of
    course at higher currents.

  10. Jim Thompson

    Jim Thompson Guest

    And IKF (current crowding at the periphery of the emitter).

    ...Jim Thompson
  11. And then find someone to design the dopant concentrations, 3D
    topology, and then fab the darned thing.

  12. Jim Thompson

    Jim Thompson Guest


    ...Jim Thompson
  13. lemonjuice

    lemonjuice Guest

    Well I didn't see she/he mention any current level ... or did I miss
    BTW having Vbe = 0.8V is equivalent to have a voltage source of 0.8V
    between the base and emitter.
    I heard its going to hotter tomorrow in Phoenix ... take your hat or
    wig with you . :)

  14. Jim Thompson

    Jim Thompson Guest

    Really ??

    I think you should leave the transistor instructions to me ;-)
    I'm heading out the door in just a few minutes to Tombstone, for the
    150th Anniversary Reenactment of the Gunfight at OK Corral ;-)

    Max temperature 80°F, night time low of 45°F.

    ...Jim Thompson

  15. Let us know how it compares to the original. ;-)

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  16. Jim Thompson

    Jim Thompson Guest

    LOUD! In the original, 30 shots, three dead, two wounded seriously...
    elapsed time 35 seconds.

    I earlier incorrectly said 150th Anniversary, it was the 125th, but
    they reenacted everything, including the funeral procession... about
    10 city blocks long... quite the deal for 1881.

    Only the family wore black, the celebrants wore white... since the
    Clantons and the McLaury Brothers were Democrats.

    No joke, that is for real ;-)

    Virtually NO Democrat candidate's signs visible in all of Cochise
    County, so I suspect bad blood to this very day.

    Altogether I took 58 photographs. I'll post them when I have a free

    Also saw a marvelous amateur rendition of HMS Pinafore, performed on
    the same stage as it was in 1881.

    The reenactment of HMS Pinafore had the Earps arresting the actor,
    portraying the admiral, for public drunkenness, and Doc Holliday
    stepping forward, "I'll be your huckleberry", and taking over the
    part. I suspect this was only a gag, but I'll inquire to see if it
    really happened.

    Had a lot of fun, ate a lot of steak and prime rib (try and get
    anything else ;-)

    ...Jim Thompson
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