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POE with LTC4267-1

Hi all

I have a problem with LTC4267-1. I try to use it for an application but when I connect it to the switch the output voltage instead of being 12V as foreseen by the diagram oscillates between 12V and 0V

I attach the schematics

PDF

Thanks for help!

Andrea

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  • Hi Eric 

    Thanks for your reply.

    PDF

    Unfortunately i can't find the MOC211M ...
    During this time I redesigned the board and set the output voltage to 5V.
    I have some improvements there but the circuit still doesn't work.
    In input I have the correct voltage coming from the ethernet switch (the switch LED indicates a connected POE device) but PVCC is equal to 0.6V and the Q1 mosfet is short-circuited DRAIN and SOURCE.
    I have already tried to replace LTC4267, Si3440DV and PA1137 but as soon as I connect to the switch the situation reappears.

    PS I find the same behavior if I change the transformer with a PA1138 and if I change the resistors R9 and R10 to have an output voltage of 12V

    thanks for yours help

Reply
  • Hi Eric 

    Thanks for your reply.

    PDF

    Unfortunately i can't find the MOC211M ...
    During this time I redesigned the board and set the output voltage to 5V.
    I have some improvements there but the circuit still doesn't work.
    In input I have the correct voltage coming from the ethernet switch (the switch LED indicates a connected POE device) but PVCC is equal to 0.6V and the Q1 mosfet is short-circuited DRAIN and SOURCE.
    I have already tried to replace LTC4267, Si3440DV and PA1137 but as soon as I connect to the switch the situation reappears.

    PS I find the same behavior if I change the transformer with a PA1138 and if I change the resistors R9 and R10 to have an output voltage of 12V

    thanks for yours help

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