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PMP41017: Clarification on Transformer Reference Designators (TRAN1–TRAN4) in PMP41017 3-kW Two-Phase Interleaved LLC Reference Design

Udhayakumar V
Prodigy 40 points

Part Number: PMP41017

I am studying the PMP41017 3-kW Two-Phase Interleaved LLC Converter reference design and have a few questions regarding the transformer implementation. I would appreciate your clarification.
1. Transformer Reference Designators
From the primary-side schematic, I observed the transformer reference designators as TRAN3 and TRAN4, whereas on the secondary-side schematic the corresponding transformer symbols are labeled TRAN1 and TRAN2.

However, the BOM lists:
TRAN1, TRAN2 – SunLord, Part No. ATWPPQ322127A200P
TRAN3, TRAN4 – YAXIN Electronic Tech, PQ32 Transformer

Could you please clarify:
Are TRAN1 and TRAN3 the primary and secondary representations of the same physical transformer, or are they different?
Similarly, are TRAN2 and TRAN4 related to the second LLC phase?
If they are separate components, could you explain their individual functions in the converter?

  • +1
    TI__Expert 7050 points

    Hi,

    Both SunLord and Yaxin has customized this transformer to me, so these two transformers are left in the BoM.

    As you mentioned, one side is connected to primary side, and the other is connected to the secondary side. They are two different boards.

    But I need to say, both of these two designs are not good for mass product, though their electrical performance is OK, their tolerance makes them hard to assemble. 

    So, you need to redesign them with your magnetic vendors.

  • +1 in reply to Desheng, Guo
    Prodigy 40 points

    Thank you for your explanation. I understand that the primary and secondary circuits are implemented on two separate PCBs.

    I have a few additional questions regarding the implementation.

    I am a little confused because the BOM contains two customized transformer entries (SunLord and Yaxin). Are these simply two approved vendor options for the same transformer, or are two physical transformers used per LLC phase to interconnect the primary and secondary boards? In other words, is the interconnection between the two boards achieved using a single transformer per phase, with its primary winding on the primary board and its secondary winding on the secondary board? Could you please explain how the primary and secondary boards are mechanically and electrically interconnected in the PMP41017 reference design? Specifically, I would like to understand how the transformer is mounted and connected between the two boards.

    I would appreciate any guidance or recommendations you can provide regarding this.
    Thank you for your continued support.