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UCC28740: Question about the choke in design

Hoang Manh
Intellectual 380 points
Part Number: UCC28740

Dear,

Firstly, please help take a look at the attachment for our AC-DC design, this design is base on one of TI UCC28740D reference design, convert 85V-265VAC to 5VDC@3A.

The design is working well so far, the next step is that we want to reduce the BOM cost and want to change some components on our design. In AC-DC design, we was using a Wurth Common Choke as a EMI filter at VAC input, this choke's price is little high and we want to replace with the cheaper one. The RefDes of the Choke is L44 in our schematic.

1/ Wurth Common Choke (PN: 7448012501) Spec's:
a. 1mH @ 10kHz
b. Current Rating: 2.5A
c. 55mOhm
d. VAC rating: 250V

2/ The new one - Kelmet Common Choke (PN: SC-01-10G) Spec's:
a. 1mH @ 100kHz
b. Current Rating: 1A
c. 70mOhm
d. VAC rating: 250V

Question: Is the Kelmet Common Choke good enough to replace the Wurth's one? Do you think current rating 1A is enough for this circuit?


Attached datasheet of both Chokes for the reference.

Please help give me any ideas.

Thanks and Best Regards,
Hoang

PWR_BOARD_SCH_REVA_29DEC.pdf

7448012501.pdf

KEM_LF0011_SC-G-GS.pdf

  • 0
    TI__Guru 66135 points
    Hello Hoang,

    The average current going through that common mode choke should be roughly 230mA.
    I estimated this based this on average minimum input voltage of 76.5V DC and 85% efficiency.
    If you add 2.0 times for margin that would be roughly 461mA The current will also be peak charged at roughly 50 to 60 Hz. So the choke you are looking at should functionally work in the circuit. However, the function of this choke is to reduce the designs EMI signature. You would have to check it to make sure it still passes EMI specifications. Safety, reliability and production qualification testing will also have to be conducted as well.

    Regards,

    Mike
  • 0 in reply to Mike O'
    Intellectual 380 points
    Hi Mike,

    Thanks for your answer, I will consider the EMI signature.

    Hoang