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Good Transformer Design primer

Discussion in 'Electronic Design' started by Martin Riddle, Oct 6, 2003.

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  1. Can anyone point me in the right direction to either a web site or text for transformer design?
    I have some experiance, but there are a few things that still stump me.
    (low freq, and high freq, pulse would be good too)


  2. "Electronic Transformers and Circuits," Reuben Lee
    "Transformers for Electronic Circuits," Nathan Grossner

    (for smaller transformers)


  3. Texas Instruments' "Magnetics Design Handbook" is pretty comprehensive.
    They have both a PDF version of all the info as well as narrated slides
    available using TI's online training service (both are free).

    Go here to get the goods:

    The single most important formula to know (IMO) is the following:

    (Winding Turns)=(Volts Applied)/[2*(Frequency)*(Core cross sectional
    area)*(delta B max)]

    All units in SI quantities, and this formula applies to transformers that
    will be seeing squarewaves (it is ever so slightly different for sinusoids,
    the factor "2" appearing in the denominator is slightly larger). This
    formula tells you basically how many turns a given winding will need on your
    core to prevent core saturation. Delta B max is the maximum flux density
    swing your convertor will be operated with. For half bridges and full
    bridges this can be as much as 2X the saturation flux density of your core
    (although in real applications it is often beneficial to use a much smaller
    limit). For forward converters this is at most only 1X the saturation flux
    density of the core. This formula does not apply for flyback transformers.
  4. Allen Windhorn wrote...
    I'd add the classic book: "Soft Ferrites," by E.C. Snelling

    There're a few good tutorials on the web for designing PWM
    SMPS switcher power-supply transformers, such as the TI web
    site, where fine stuff from the classic Unitrode Seminars
    collection is online. There you can find two Dixon articles
    on magnetic-core models in slup109 and slup128 (the latter
    also has other articles). I have a 12MB file in my computer
    called, which contains Lloyd H.
    Dixon's lengthy article: Magnetics Design for Switching Power
    Supplies (in slup123 through slup127), plus slup 128.

    - Win

  5. Thanks all.
    I had heard Unitrode had great tech info, didnt know magnetics was among it.
    I'll check the TI web site.
    You mentioned Flux Density, I allways had difficulty understanding where this number came from.
    I was told to use 3kgause for Ferrite ( if I remember right) and this number could change as
    personal perference dictated.
    I guess this should be in some text somewhere.


  6. Active8

    Active8 Guest

    you mean saturation flux density.

    if you google on "Producing wound components", you'll find a site that
    may explain this. i e-mailed the author and he zipped that part of the
    site up for me (possibly the whole "ESU advisor" site - you can search
    on that, too), but he didn't put the link up. he mentioned that he might
    leave it up if more requests came in. i'd post it to binaries group but
    it's not my site to do that with.

    anyway... this will help explain things. i think you'll find an
    explaination of how AsubL values are computed for cores. then you can
    check the amidon (or whoever) site for AsubL values and saturation flux
    densities. IIRC the latter is in graph form. you have your work cut out
    for you AFAIC, but you'll learn a lot. theres info on mfg sites for
    switchers and magnetics companies.

    hope this helps,
  7. Thanks, Thats a great site. lots of info, all in one place.


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