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TIDA-00961: Question about inductors

Chan Chung Ying
Prodigy 30 points

Part Number: TIDA-00961
Other Parts Discussed in Thread: UCC28050, UCC28060

1. In the reference design document, the boost inductors L1=L2=14.78uH are determined by Pout=1600W.

But there are two inductors, why can't use 800W for each inductor?

2. Since the inductor current goes to negative area to achieve ZVS. Does the quadrant of B-H curve of the inductor can be assumed I and III?

  • 0
    TI__Expert 3860 points
    Hi Chan,

    In the given equation, the two phase operation is already factored in. 15uH is the value required for 800W.

    Yes, the operation of the inductor will be in I & III quadrants. However, since the negative current is much lower than the positive current, the flux is predominantly in first quadrant only.

    Regards,

    Salil
  • 0 in reply to Salil
    Prodigy 30 points

    Hi Salil,

    For inductance, below are listed in the document but Pout was used 1600W rather than 800W. May I know how to factored in?

    L1=L2=(eff x Vin^2 x Dpeak_LL)/(Pout x Fmin)

    where eff=0.99, Vin=160V, Dpeak_LL=0.42, Pout=1600W and Fmin=450kHz, the calculated value of L1 and L2 are 14.78 μH.

    The value of the boost inductor was rounded off to 15 μH.

  • 0 in reply to Chan Chung Ying
    TI__Expert 3860 points

    Hi Chan,

    Please refer to the inductor calculation in UCC28050 (single phase transition mode controller) datasheet:

    And now compare with inductor claculation in UCC28060 (interleaved transition mode controller) datasheet:

    Comparing these two, we can see that the '2 * Pout' term in the single phase equation has been replaced by 'Pout' in the two phase equation. This accounts for the correction factor for two phase operation. In effect, the power has been reduced by half in the two phase operation equation.

    Hope this clarifies.

    Regards,

    Salil

  • 0 in reply to Salil
    TI__Expert 3860 points

    Hi Chan,

    Sorry, I attached the same equation for both.

    For UCC28050, please see the correct equation below:

    Regards,

    Salil

  • 0 in reply to Salil
    Prodigy 30 points
    Hi Salil,
    Thanks for replied, I'll take at look UCC28050 and UCC28060.