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Magnetics modules for LAN

  1. Jan 29, 2014 #1
    Hi, Guys I have a B78476A8135A003 Magnetic Module from EPCOS and I want to add a surge protector either on the TJ45 connector side or the Ethernet PHY side. I cant decide which way is more beneficial. Here is the topology:

    Ethernet PHY : B78476A8135A003 : Surge Protector (SLVU2.8-4) : RJ45
    Ethernet PHY : Surge Protector (SLVU2.8-4) : B78476A8135A003 : RJ45

    Also, the datasheet of B78476A8135A003 doesnt talk about its surge or ESD specs. How can I determine those specs?

  2. jcsd
  3. Jan 29, 2014 #2


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    Staff: Mentor

    Welcome to the PF.

    Does the Surge Protector not come with some application note?
  4. Jan 29, 2014 #3
    Hi, Thanks for your reply. Yes you are right it did come with the application note. However, the application note is actually the options mentioned above. It does not go into the benefits of either topology over another. I am mainly interested because lets suppose a surge happens, then Magnetic module (1:1 ratio transformer for Tx and Rx) in theory should help diminish the effects of the surge because its composed of couple of inductors. If I add a surge protector component the following way:

    Ethernet PHY : B78476A8135A003 : Surge Protector (SLVU2.8-4) : RJ45

    then the surge protector components needs to have higher spec which means >$ and >size.
    However if the other topology is used then I can lower the spec of the surge protector which will allow me to use small package size (very important for my pcb as I have very little space).

    Your thoughts!
  5. Jan 29, 2014 #4


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    Staff: Mentor

    Can you give a link to the application note?

    I don't work with Ethernet PHYs much, but I do work with other types of communication networks. I usually put the primary transient protection at the network input (your RJ45) before the transformer. Then I put secondary transient protection after the transformer before the transceiver silicon (usually just clamp diodes to the rails). The primary protection shunts most of the transient energy to Earth ground, so only a little is left to couple through the transformer.
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