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PoE PSE Isolated DCDC Converter 12V/48V

Christian Merk
Prodigy 30 points
Other Parts Discussed in Thread: PMP7899, PMP, TPS43060EVM-199

Hi,

i need a power supply for a PSE (802.3af) with 4 Ports (~60W). If  i'm right, the power supply and the

PSE part has to be isolated to the rest of the cuircit (NIC etc..). 12V are available, but i need ~48V so i have

to design a DCDC boost converter, but i can't find any ANs oder reference designs for isolated converters (except PMP7899).

Are there any information, especially about dimensioning the transformer, which can help me to design it?

I thought this would be a standard application, but it's hard to find information about this kind of converter.

Thanks in advance,

Chris

  • 0
    TI__Mastermind 42795 points

    Most of the boost converter designs that I've located are non-isolated (TPS43060EVM-199 for example which is available for order). A flyback might be a better choice but I could not find any PMP reference designs on the TI web site. You may be able to find a few more ANs for flybacks. I've attached a schematic for PMP2429C which is a 53V/1A flyback and the transformer is available from Coilcraft. I confirmed that we have tested a 10-18V input rated transformer design using this circuit, but could not locate the documentation. You may be able to contact Coilcraft for an equivalent to the GA3136-AL with a lower input operating range.

     

    PMP2429_RevB_SCH.pdf
  • 0 in reply to Eric Wright
    Prodigy 30 points

    Thanks, i will look for some flyback designs, maybe i find something suitable.

    The PSE is within a PC, powered by an ATX power supply. Just to be sure: The PoE power must be isolated to the PC-components? Because it's easier / cheaper / faster  to design a non-isolated converter, but i read in the 802.3af standard that it is necessary (?)

  • 0 in reply to Christian Merk
    TI__Expert 7990 points

    Isolation to things like frame ground is necessary.  The twisted pair ethernet network itself floats. 

    See IEEE 802.3at or IEEE 802.3-2008 (current revision) clause 33.4.  These specifications are available for download over the internet (http://standards.ieee.org/about/get/802/802.3.html).  You might also consult IEC/EN/UL 60950-1.  There is a section on safety regarding TNV networks and devices.

  • 0
    Prodigy 130 points
    Hi, I'm thinking of using a similar circuit for a similar application (using ATX PSU for getting isolated 48V PoE), thanks for asking this question