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flyback transformer design

zahra sq
Prodigy 190 points

Hi everyone

I want to design transformer for flyback converter. I read some application notes of texas instrument like: Magnetics Design Handbook by Lloyd H. Dixon, Jr  and Transformer and Inductor Design for
Optimum Circuit Performance. they were very useful but I don't know what type of core material I should use. in their text was said : magnetics type p material used for CCM mode and magnetics type k used for DCM mode. what are type p and type k ? How can I choose the core material?

Thanks,

Zahra

  • 0
    TI__Genius 13660 points
    Hi Zahra,
    Each magnetic manufacture has different naming method for core material. I can't explain what magnetics type p and type k are. You need to find their specifics parameter of core material from the corresponding manufacture.
    Regards,
    Teng
  • 0 in reply to Teng Feng
    Prodigy 190 points
    Hi Teng,

    thanks for your help
    How can I choose a proper core material for a flyback transformer?

    Zahra
  • 0 in reply to zahra sq
    TI__Genius 13660 points
    Hi Zahra,

    Core losses is the most consideration while chose a core material for a flyback transformer. The mostly often used core material is ferrite core in flyback topology stage.
    Core losses occur in the transformer’s ferrite core and depend on the core’s flux density (amplitude, duty cycle and flux-density rate of change), frequency of operation, core size or volume, and properties of the chosen ferrite material. Different materials optimized for different frequency and peak flux-density ranges will exhibit varying core-loss characteristics.
    The ferrite core losses per unit volume can be written as: Pv= CT * η * f^(α) * B^(β)，
    In this equation, α=1.2~1.7, β=2.2~4. f is operating frequency. B is flux density. CT is the temperature coefficient of the loss of ferrite material, CT=1 at 100℃. η is material coefficient, for the coefficient of each material, please refer to the manual provided by magnetic manufacture.
    In summary, please chose the ferrite material which can make the core losses minimum.
    Regards,
    Teng
  • 0 in reply to Teng Feng
    Prodigy 190 points
    Hi Teng,

    many thanks for your Complete explanations.
    would you please tell me what is the reference of the formula that you wrote?
    And in both DCM and CCM mode should we just consider core loss to choose core material?

    Best Regards,
  • 0 in reply to zahra sq
    TI__Genius 13660 points

    Hi Zahra,

    This is a basic formula for calculating core losses. You can search the key words "core loss formula" or find some papers about magnetic component yourself.

    For example:  https://www.mag-inc.com/Design/Design-Guides/Powder-Core-Loss-Calculation

    It may say so, we first consider core loss to choose core material for both DCM and CCM mode. But it need to pay attention that magnetic flux swing should satisfy the requirement for CCM mode because its DC offset.

    Lastly, I think this is a magnetic issue, not a IC issue. If you interests it, please learn more form magnetic  technical guideline.

    I am closing this thread.

    Regards,

    Teng

  • 0 in reply to Teng Feng
    Prodigy 190 points

    Hi Teng,

    thanks for your help.

    Best Regards,

    Zahra