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small multilead HV transformers

Discussion in 'Electronic Design' started by Jamie Morken, Feb 5, 2008.

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  1. Jamie Morken

    Jamie Morken Guest

    Hi,

    I have an application that needs 4 isolated secondaries all with about
    1kV isolation, for supplying floating fet gatedrivers. Does anyone have
    a transformer part that would be small and still UL certified for
    500Volt pin spacing, like 0.1" or more.

    cheers,
    Jamie
     
  2. Life will become *much* easier if you use four separate 1:1 pulse
    transformers - they are easy to get, the layout is simpler because now you
    got space for the correct creepage distances (and maybe cutouts) and more
    robust. I have done many field repairs of 1:1:1 pulse transformers for
    inverters where the breakdown was precisely between the two secondaries!

    Anyway, In the past I have sucessfully used a primary winding of coax
    threaded though a string of ring-cores with multi-turn secondaries for that
    kind of application. The first of those are probably still running
    somewhere - i.e 24/7 for 8 years (3.5 kV RADAR modulator).

    The secondaries are wired as current-transformers with a (low-value!!)
    resistive load yielding the proper gate voltage, the primary used 28V DC to
    get enough drive. That was with a string of 20 MOSFET's so yours will be
    different.

    It is important to connect the coax shield to something "stable" to reduce
    capacitive losses and corona/arcing. I used a resistive divider made from
    the bleeder resistor to set the shield at 6 Kv. (The switch was running at 8
    Kv). Ring cores "sit" really well in a board if one makes cutouts so that
    about 1/4-1/3 of the completed core fits into the cutout, fit the cores,
    then dab each with some hotmelt glue and thread the coax.
     
  3. legg

    legg Guest

    It's important to identify and differentiate safety and functional
    isolation reqirements. Safety isolation requires spacings and
    insulation layer/thickness redundancy that exceed functional
    requirements and may not be physically achievable in smaller parts
    using conventional assembly materials an methods.

    UL does not consider pin spacings for functional isolation to be a
    certification issue, In the application it becomes one of single-fault
    abnormal performance. Small 1:1:1 pulse transformers can be
    constructed for functional 500V isolation to one of the windings, but
    this winding needs to be identified and terminated characteristically.
    This is not a jellybean telecom pulse application.

    RL
     
  4. John Larkin

    John Larkin Guest

    IDSN telecom line transformers are great. Small, cheap, fast, 1500
    volt rated.

    John
     
  5. Joerg

    Joerg Guest

    How about two of these?

    http://www.tamuracorp.com/clientuploads/pdfs/engineeringdocs/G504.pdf

    Triad would be a good place, too, but their web site has been screwed up
    so badly that it's now inaccessible (at least for me).
     
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