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SPICE newbie question

Discussion in 'Electronic Design' started by Pete Clark, Jun 9, 2006.

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  1. Pete Clark

    Pete Clark Guest

    Hi,

    I want to know how to vary a parameter inside a model and get the
    results in one run (one simulation). I've given a simple circuit below
    that I would also want to do .TRAN and .AC analysis on. (Like run an AC
    response for three transistor values of Bf.) I've managed to do .TEMP
    parameterization, but I can't figure out how to do something like Bf.

    For the purpose of example, what syntax would I add to parameterize the
    Beta_forward (Bf) to values of 50, 125, and 300? (The model is the one
    that comes with LTSPICE, BTW.)

    I have been trying to learn on the latest version LTSPICE, if that
    matters.

    Thanks,
    Pete

    Here is an example circuit:
    ---------------------------


    2n3904_00
    * Vcc
    * .-----.
    * | |
    * ---V1 |
    * - 5V .-.
    * | | |R1
    * === | |2k7
    * GND '-'
    * |
    * .-----o
    * | |
    * .-. |Vc
    * | |R3 |
    * | |13k |
    * '-' |
    * |Vb |/ 2n3904
    * o---| Q1
    * | |>
    * .-. |
    * | |R2 |
    * | |6k8 |
    * '-' |
    * | |
    * '-----o
    * |
    * ===
    * GND
    *
    *
    *(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

    Q1 Vc Vb 0 0 2N3904
    R1 Vcc Vc 2.7k
    R2 Vb 0 6.8k
    R3 Vc Vb 13k
    V1 Vcc 0 5
    ..model 2N3904 NPN (
    +IS=1E-14
    +VAF=100
    +Bf=300
    +IKF=0.4
    +XTB=1.5
    +BR=4
    +CJC=4E-12
    +CJE=8E-12
    +RB=20
    +RC=0.1
    +RE=0.1
    +TR=250E-9
    +TF=350E-12
    +ITF=1
    +VTF=2
    +XTF=3
    +Vceo=40
    +Icrating=200m
    +mfg=Philips
    +)
    ..op
    ..end
     
  2. Others are more familiar with it but if you stick the text ...
    ".STEP NPN 2N3904 (BF) LIST 50 100 300" somewhere on the circuit, then 3
    superimposed runs will be made.

    Or do ".STEP NPN 2N3904 (BF) 50 850 10" and 80 runs will made, from 50 to
    850, in steps of 10.
    john
     

  3. Hello Pete,

    There is an example with parameter variation in the directory "examples" of
    LTspice.
    .....\examples\Eucational\stepmodelparam.asc

    The syntax for the .step command line
    --------------------------------------
    Example for Bf = 50 to 100 step 25

    ..step NPN 2N2222(Bf) 50 100 25


    Example for Bf = 50, 125, 300

    ..step NPN 2N2222(Bf) list 50 125 300

    In the future you should better share your schematic file (.asc).
    Just copy the contents of your schematic file (.asc) into your message.
    It's pure ASCII text.

    Best regards,
    Helmut

    The Yahoo group with a lot of circuit examples.
    http://groups.yahoo.com/group/LTspice/
     
  4. Pete Clark

    Pete Clark Guest

    Thanks so much to you and John. I really appreciate it!
     
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