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TPS40210: SEPIC Coupled Vs Uncoupled Inductor Calculation

Anand Kumar6
Prodigy 150 points
Part Number: TPS40210

Tool/software:

Dear all,

 My query is related to the article “Benefits of a coupled-inductor SEPIC converter” by the author: John Betten at Texas Instruments.

 The doubt was related to using coupled inductors Vs uncoupled inductor. In the document, the three equations related to coupled and uncoupled inductor were published.

 

 For the below design requirements published in the article, its mentioned that the prototype with coupled inductor used a value of 12uH and that with uncoupled inductor used 33uH for L1 and 22uH for L2.

 

 But when I apply these requirements into the three equations mentioned above, I ended up with some other inductor values, which do not match with the ones mentioned in the article.

 

 Please help calculating the right inductor value for SEPIC for a coupled and uncoupled inductor based on the formulas given in the article.

 

Regards

Anand

  • 0
    TI__Mastermind 30160 points

    Hi Anand,

    Thanks for using the e2e forum.
    Unfortunately the creator of this app note already retired, so we cannot ask him directly.

    We have another SEPIC design app note available, which can be found here:
    https://www.ti.com/lit/an/snvaa43/snvaa43.pdf
    I can also confirm that the quickstart calculator for TPS40210 uses a coupled inductor in its equations.

    Another helpful tool for calculating inductance for coupled and uncoupled inductors is the power stage designer:
    https://www.ti.com/tool/POWERSTAGE-DESIGNER

    I am not sure if reading into several formulas will improve the understanding and explain the mismatch of results, or if this will only create more confusion.

    Please let me know if additional help is required.
    Best regards,
    Niklas

  • 0 in reply to Niklas Schwarz
    Prodigy 150 points

    Hi Niklas,

    Thank you.

    I tried to download the POWER-STAGE DESIGNER. But it showed the message below. So please help to get the SW downloaded.

    Secondly, are there any documents that helps in uncoupled inductor calculation for SEPIC converters?. If so, please share.

    Regards

    Anand

  • 0 in reply to Anand Kumar6
    TI__Mastermind 30160 points

    Hi Anand,

    The Power Stage Designer tool can calculate both for coupled and uncoupled inductors.
    I am sorry to hear that you get an error when trying to download the tool.

    I cannot help with access permission from my side, so you would need to set up another ticket regarding the transaction denial.
    In the meantime, you can also check this app note. The calculations in the Power Stage Designer tool should be based on the formula here:
    https://www.ti.com/lit/an/slyt309/slyt309.pdf

    Best regards,
    Niklas