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Transformer direction between PoE and non-PoE

Toshihiro Watanabe
Genius 10235 points

Hello,

I would like to ask about the transformer direction between PoE and non-PoE.

Non-PoE ethernet application, I think typically common mode choke coil side of transformer is RJ45 (cable) side.

When PoE ethernet application, It seems common mode choke coil is opposite side of RJ45 (cable) side.

I guess above configuration would be typical for these use case. Is there implicit rule of transformer direction like above?

I guess transformer direction is opposite would be PoE transmit the power via cable so flowing current through choke coil may be not good in some reasons.

Would you let me know if there is an implicit rule for transformer direction?

Best regards,

Toshihiro Watanabe

  • 0
    TI__Mastermind 41790 points

    Hi Watanabe-san,

    There is no implicit rule for the data transformer. I've seen chokes that are on the data side and chokes on the power side. Either way, the choke will help with the data; however from a power prospective, I typically see chokes on the data side for higher power PoE applications. This makes sense since the higher current would require a larger choke if placed on the PoE side. For lower power applications, I've seen the choke on either side.

    Rather, I highly recommend simply looking at the datasheets of the data transformers. It will say which side is the power side and which side is the data side regardless of where the choke is.

    Thanks!

    Regards,

    Darwin