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LM5046: There is the that used AN-2126 the LM5046here are a few questions

Dietrich Rushing
Prodigy 81 points
Part Number: LM5046

Tool/software:

Hi,

So i was looking at the LM5046 chip and i was studying this document and i could not find the transformer core used in this design.

What ER? cor was used was it ungapped or not?

Also do you think FB can be achieved with optoemulators?

C13 C6 shouldn't these 2 have been Y1/2 safety capacitors? Also i don't really understand how they can reduce noise or their role in general when used across the safety gap. Do you have any resource to help me like some application note or article?

Best regards,

  • 0
    TI__Guru 73345 points

    Hi,

    Page 9 of AN-2126 shows the transformer core cross section which is ER core. No gap is necessary as we know in 48 V applications phase shifted full bridge and symmetrical full bridge do not show efficiency difference based our test.

    Yes ok to use  an optoemulator to FB.

    C13 and C6 are y cap.

  • 0 in reply to Hong Huang
    Prodigy 81 points

    Hi,

    For C13 C6 when i googled that part number it was not a Y cap on mouser but it is an old part anyway , important is that u confirmed it is a Y cap.

    Great in another design i could not but now i can finally ( on my LLC du to IC reasons i could not) increase reliability with optoemulators.

    Yes i can see it is an ER core but i can t really measure what well on the PDF, centr seems to be about 15-17mm and outline is about 25x35mm. I was initially looking for a part number but since it is ungaped i can guess sort of well the series. The material is the only thing that i would like to know tho i guess it is N89 or N87 ?

    Also i didnt find the Lmag value of this transformer, i wanted to know it mostly to compare that the TI calculator sais it is a minimum required and the actual used on the PCB.

    Best regards,

  • +1 in reply to Dietrich Rushing
    TI__Guru 73345 points

    Hi,

    C13 and C6 are in series connection, 3300pF each rating, in telecom usually 1500pF rating is enough, so that is why using non -y cap to do y-cap function.

    The inductance should be between 200uH and 250uH from our design experience when in the range of 100W to 700W design with such devices. The application note was published long time ago. We do not know where the author is to get what core material is. I think you can use 220uH, and 300kHz to 600kHz frequency to find a proper material within that geometry size. I think you do not have to know exact size of the core since the core size should be standard so a rough size can lead you to a proper standard.

  • 0 in reply to Hong Huang
    Prodigy 81 points

    THX, yea i expected about thatfor the inductance but i was in search of area to have some confirmation bias. I was interested in the core material mostly since i was considering ways to reduce the winding count in order to reduce layer count but now with this i can work alone for a looong time,

    THX again for your assistance.

  • 0 in reply to Dietrich Rushing
    TI__Guru 73345 points

    Hi,

    A possible one is 3C95 or similar from similar designs.