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SPICE models for diac?

Discussion in 'CAD' started by Chaos Master, Jan 3, 2004.

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  1. Chaos Master

    Chaos Master Guest


    I'd like to know if some manufacturer ever created SPICE models for Diac's. I've
    searched and didn't find one. Can someone post a model of diac on this group?

  2. Jim Thompson

    Jim Thompson Guest

    Is a Diac the same as a UJT/Unijunction-transistor?

    ...Jim Thompson
  3. No, it's a bidirectional avalanche device- more like a triac. There's
    one in every consumer light dimmer. Breaks down at something like 30V
    (either way) depending on type and stays on until the current drops
    below the holding current. The schematic symbol is a triac with no
    gate connection.

    The classic 2-wire light dimmer circuit is an adjustable R to a C
    across the triac, with a diac from the C to the gate of the triac. The
    triac gets pulses of opposite polarity every half-cycle, triggering it
    in quadrants I and III.

    Best regards,
    Spehro Pefhany
  4. I found this on the site (->Site Map->Discuss->Pspice

    Topic: Spice Modeling
    Author: Rabin
    Date: 10/01/2002 5:20:41 PM

    Subject: RE: DIAC
    << previous thread < previous next > next thread >>

    There is a generic Triac model in PSpice's Thyristr
    library which should be able to be modified for a Diac by disabling the gate
    trigger circuitry in the model.

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  5. Jim Thompson

    Jim Thompson Guest

    Aha! A solid-state equivalent of an NE-2 ?:)

    Should be easy enough to make a subcircuit from a data sheet.

    But do they make them anymore, or is it just a hacker component?

    Surfing gave poor results, but finally stumbled onto Intusoft's stuff

    ...Jim Thompson
  6. The grandpappy of them all (can't you tell from that 1960's

    Current production: Data/Diac HT and ST Series.pdf
    They make them, and they are cheap enough (<< 2 cents in 200K) but
    AFAIK they are not really in wide use other than for triac triggering
    in light dimmers. have them built-in.
    Best regards,
    Spehro Pefhany
  7. Hello "Chaos...",
    I have answered a similar question a few months ago in the LTSPICE
    Yahho group. The modeled DIAC triggers at +/-32V. I think the DIAC
    symbol is already available in "Misc" folder of LTSPICE.

    Best Regards,

    Original text from thread 728 follows:

    Hello ....,
    I have done a big search about DIAC models with Google. It is really
    strange how less useful information I could find for a SPICE model.
    The best I have found is in the Intusoft newsletter Spring 2002.

    I have made a DIAC model based on the Spectrum-Soft DIAC circuit plus the
    data sheet from Teccor and my personal knowledge. You can adjust the
    trigger voltage with the value of Rv. A greater value gives a higher
    firing voltage. The breakover current is set by the value of R1 and
    R2. Teccor specify 25uA, but I have seen another company specifying
    100uA. With the 10kOhm values it is about 60uA. I believe this model
    is very realistic compared with the data sheet. Files/Power/E8 Diac.pdf

    ..SUBCKT DIAC32 1 2
    RS 1 N006 10
    RV N002 N004 510k
    R1 N006 N002 10k
    R2 N004 2 10k
    Q4 N002 N005 2 0 PNP
    Q2 N004 N003 N006 0 PNP
    Q1 N003 N004 2 0 NPN
    Q3 N005 N002 N006 0 NPN
    D5 N002 N005 D
    D6 N004 N003 D
    ..model NPN NPN(BF=20 TF=5u)
    ..model PNP PNP(BF=2 TF=5u)
    ..model D D

    Best Regards
  8. Chaos Master

    Chaos Master Guest

    Klaus Vestergaard Kragelund[] said this in
    sci.electronics.cad, at Sat, 3 Jan 2004 23:02:59 +0100, in article
    <3ff73bfd$0$9746$>. I can prove it. And thus I reply:

    Interesting! I have some triac models here, from Teccor.
    As I thought, the diac is a triac without gate.
  9. Chaos Master

    Chaos Master Guest

    Helmut Sennewald[] said this in sci.electronics.cad, at
    Sun, 4 Jan 2004 01:40:45 +0100, in article <bt7neb$e68$06$>. I
    can prove it. And thus I reply:

    Thanks! I will try simulating this tomorrow, with SuperSpice.
  10. Jim Thompson

    Jim Thompson Guest

    AND a low (relatively) breakdown mechanism.

    ...Jim Thompson
  11. There is a generic diac already in SS. If you do a shift-f you get the
    find dialog. Typing diac brings it up, and you can place it from there
    with the button. Its in the GenericDemos folder.

    Kevin Aylward
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.

    That which is mostly observed, is that which replicates the most.
  12. Chaos Master

    Chaos Master Guest

    Kevin Aylward[] said this in
    sci.electronics.cad, at Sun, 4 Jan 2004 11:16:42 -0000, in article
    Ahhhh... I didn't knew this.
    Thanks for all that replied.
  13. Active8

    Active8 Guest

    Is that what they're calling the silicon bilateral switch - a TRIAC
    w/ built it DIAC sort of? not a pnpn npnp thing but 4 trannys, 2
    zeners and 2 R's that act like a DIAC input TRIAC?

    Now we have the SIDAC which looks like it's a DIAC with higher
    breakover voltage. That lib below is sort of a hint and it opens
    right up in model editor :)
  14. Chaos Master

    Chaos Master Guest

    Active8[] said this in sci.electronics.cad, at
    Mon, 05 Jan 2004 19:45:59 GMT, in article

    Typing "silicon bilateral switch" into Google gives some results (~300), which


    I am too tired to read them all, but I think this answers something about silicon
    bilateral switches.
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