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transformer for LT SwitcherCAD

Discussion in 'Electronic Design' started by Ira Rubinson, Jun 9, 2006.

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  1. Ira Rubinson

    Ira Rubinson Guest

    Does anybody know how of a transformer that I can add to the component
    library for Linear Technologies SwitcherCAD? I'm trying to simulate a
    switching power supply.
    Thanks -Ira
     
  2. Genome

    Genome Guest

    Without getting too wordy about things have a look at....

    http://www.genomerics.org/smps/offconv/offline.html

    For the general idea for an ideal transformer in SPICE.

    You take that idea and then add 'parasitics' as required.

    You might get leakage inductance by playing with the coupling coefficients
    but it is easier to make them all 1 and then add series inductance to the
    appropriate windings.

    DNA
     
  3. Fred Bloggs

    Fred Bloggs Guest

    I have never used SWCAD but do know it is optimized especially for
    switchers. In a pinch, certainly you can find an ideal transformer, then
    parallel it with an inductor equal to the magnetizing inductance, and in
    series, with the whole assembly, add a combo of R+Ls where R is the
    winding resistance and Ls is the leakage inductance, which can be taken
    to be 1% of magnetizing inductance. Add a secondary series R+L as well.
    This will give a first order approximation. For an exact simulation
    SWCAD should have provisions for a Jiles-Atherton [sp?] transformer
    simulation, mainly to simulate core losses, and this requires
    information pertaining to core material and geometry- much more
    detailed. You can also estimate the loss and represent this in the first
    order model by a resistor Rm in parallel with the magnetizing
    inductance, which is still useful for obtaining bounds.
     
  4. Think I found this on the yahoo gloops LTSpice

    Lp N003 N004 Lp
    Ls N005 N006 Ls
    Llp N001 N003 Llp
    Lls N005 N008 Lls
    Rp N004 N002 Rp
    Rs N006 N007 Rs
    Cs N008 N007 Cs
    Cp N001 N002 Cp
    Rc N003 N004 R
    K1 Lp Ls 1
    ..backanno
    ..end



    martin
     
  5. Fred Bloggs

    Fred Bloggs Guest

    Just another first order with no core loss or nonlinearity representation...
     
  6. colin

    colin Guest

    The easy part is you use an inductor for each winding then link them all
    with the K directive.

    This provides an ideal transformer, you can then model the losses wich are
    frequency dependant with L/R/C circuits around the winding inductance, or
    even use the parasitic parameters of the inductors.

    Some inductors specify eqv circuits in their data sheets. I dont know about
    transformers, especialy if you are winding your own, maybe there is a
    normalised circuit equivalents for each type of magnetic material ?
    obviously it would vary a lot depending on construction gap etc.

    I supose you could even model the magnetic path in circuit terms, theres a
    good ltspice forum on yahoo might have the answer already.

    Colin =^.^=
     
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