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Need Help, LTspice SCR model

Discussion in 'Electronic Design' started by amdx, Feb 24, 2007.

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  1. amdx

    amdx Guest

    Hi all, I found the following model of an SCR on the web. I have tried to
    use it in a simple circuit and I can't seem to get it to work. It barely
    turns on.
    I would like a model for a 2N5060, I don't find one.
    Is there something obviously wrong with this model?
    Or, can someone give me a model of a small signal SCR?
    Thanks, Mike
    *Extracted from PONT_DIPH.CIR file from EDN website.
    *I renamed that file as SCR_CKT.CIR
    * Anode
    * | Cathode
    * | | Trigger
    * | | |
    ..subckt SCR 1 2 3
    *Models used by the SCR Model:
    ..model STH VSwitch (ROn=0.1, VOff=0.5)
    ..model DLG D (Rs =25m)
    *We assume that the SCR in the on-state is equivalent to 0.1 ohm:
    SSCR 1 4 5 0 STH
    VSCR 4 2 0V
    *Trigger to cathode impedance is a 1k ohm resistance - fore simplification:
    RTrig 3 2 1k
    * The following circuit locks in the on-state when a 1mA current flows
    *through the gate to the cathode with a positive anode to cathode voltage.
    *This circuit locks in the off-state when the current through the SCr tends
    *to become negative:
    VPlus 6 0 2V
    SiTrig 6 5 3 2 STH
    CState 5 0 1uf IC=0
    DLogic 5 8 DLG
    HCur 8 0 poly(1) VSCR 1 10000
    *The potential of node 5 reflects the state of the SCR. It is less than 2V
    *for the off-state and between 1v and 2V in the on-stateh
  2. Hello Mike,

    The SCR symbol in LTspice has the pin order Anode, Trigger, Cathode.
    You could either make a new symbol SCR1 with the netlist order
    Anode, Cathode, Trigger or you simply change the pin order in the

    Solution 1: Change the subcircuit line

    Solution 2:

    Make a copy SCR1.asy from the synbol SCR.asy.
    Open the new symbol SCR1.asy and change the netlist order
    of the gate/trigger pin to 3 and the the cathode pin to 2 as
    required by the original subcircuit.

    Both methods are ok. Take your choice.

    Best regards,
  3. amdx

    amdx Guest

    Thanks Helmut, good call, sharp of you to notice. I had already made
    that change through the atribute editor. I'll revisit it just to make sure I
    have the labels correct.
    The change was in the writeup about the SCR file.
    Thanks, Mike
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