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Original question:

LM5155: Whether it can be used with an Isolated Flyback

LM51561: EMI countermeasures of isolated flyback

Dice-K
Mastermind 7480 points
Part Number: LM51561
Other Parts Discussed in Thread: PMP22764,
Hi support team,

I use LM51561 isolated flyback for PSE power supply of PoE.
・Input voltage：DC18V～38V
・Output power: 46W or more
・Output voltage: 54V

But I'm having problems with EMI testing.
・ EMI in the low frequency range (500kHz to 30MHz) is large.
・ The noise terminal voltage of the AC power supply and PoE port cannot pass the VCCI standard.
・ PoE power supply is affected by radio interference test and EMI noise test.
(There is a possibility that the LM51561 is affected by noise and falsely detects an overcurrent, causing a momentary interruption.)

I want to improve the board pattern.
Can the PMP22764 and LM5155EVM-FLY boards serve as a model for EMI countermeasures?
Is there any other model board?

Regards,
Dice-K
  • 0
    TI__Genius 11215 points

    Hello Dice-k, 

    Thanks for reaching out. Yes, the board PMP22764 is a very good example as it also includes two PI filters at the input and output of the Flyback, at this link you can find the layout of the board https://www.ti.com/tool/PMP22764 . Let us know if you need further support. 

    Kind regards,
    EM

  • 0 in reply to EM
    Mastermind 7480 points

    Hi EM,
    Thank you for your reply.

    Are there any examples of countermeasures when overcurrent is falsely detected by EMI noise?
    Is it the best way to bring the current sense resistor closer to the CS pin of the LM51561 and make the wiring thicker?

    If possible, I would like to send you a schematic and board pattern in a private message.

    Regards,
    Dice-K

  • 0 in reply to Dice-K
    TI__Guru 65340 points

    Hello Dice-K,

    Would you please explain what exactly you mean with countermeasures?

    In general layout is extremely important with flyback converters as there is in general noise in the system as the current on the input and output side is partly interrupted.

    After you requested a friendship with anyone you can start private communication with this specific person.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Mastermind 7480 points

    Hi Brigitte,
    Thank you for your reply.

    I sent you the schematic and board pattern in a private message.
    Would you please check the contents?

    Best regards,
    Dice-K

  • 0 in reply to Dice-K
    TI__Guru 65340 points

    Hello Dice-K,

    As we go on in private message, let me close this thread.

    Best regards,
    Brigitte