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UCC28740: about calculation file

ACGUY
Guru 11170 points
Part Number: UCC28740

Hello E2E,

Our customer designed the 10-W transformer using UCC28740 calculation file.
Result, Lp=2600-uH, Rcs=1.8-ohm.
They said Lp and Rcs are too large. I have the same opinion.
At transformer for EVM, Lp=560-uH.

Does this calculation sheet calculate the correct result?

Customer's design spec;
Vin : DC220V to DC282V, Typ 260V
Vout : 5V
Iout : 2A

Regards,
ACGUY

  • 0
    TI__Guru 73715 points

    The calculator calculates correct results based on what input numbers you put. The high inductance is due to your narrow input voltage range. The calculator result is to make DCM less deeper. You can adjust your input to get different inductance. Particularly, row 49, and cell C15 C49,  it says a lower Nps results in deeper DCM. But deeper DCM will get a lower inductance. For example, Nps = 15, 788.6uH. Nps = 10, 525uH.

    EVM has a wide input voltage range, with min 85Vac input. To maintain regualtion, Nps needs to be low so to result a low inductance.

  • 0 in reply to Hong Huang
    TI__Guru 73715 points

    Notice a typo error in the last reply. In the below, C15 should be C49.

    "Particularly, row 49, and cell C15 C49, it says a lower Nps results in deeper DCM. But deeper DCM will get a lower inductance."