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UCC28019: About the UCC28019 Avoid Audible Noise

Rock Shao
Expert 2800 points
Part Number: UCC28019

Hi Sir,

About the UCC28019 needs to provide VICOMP 6~7uA to avoid the problem of abnormal sound and I would like to ask
        1. How was the value of 6~7uA determined?
        2. What will happen if it exceeds 7uA, what is the highest acceptable current
        3. What will happen if it is lower than 6uA, and if it is not connected, only the abnormal sound problem will occur
        4. What effect will the additional current of V ICOMP have on the design and what should be paid attention to?

Wait for the answer, thank you.

Thanks & best regards

  • 0
    TI__Mastermind 34465 points

    Hello Rock,

    The concept of adding a resistor from VCC to ICOMP is to add a small bias to the current amplifier output.
    This raises ICOMP to just above the pwm ramp signal at no load.
    The idea here is to generate very narrow pulses at no load and prevent  a burst type of operation which will generate audio noise.
    This is discussed in detail in the SLUA688 Application Report.

    If you add too much bias on ICOMP then the value of VCOMP at no load needs to rise to generate the pwm signal.
    This will lower the dynamic range of VCOMP and prevent the pfc from delivering full load over the input voltage range.

    It was found by experiment that adding a 6uA to 7uA bias from VCC is the most effective method to prevent audible noise at no load.

    Regards

    John

  • 0 in reply to John Griffin1
    Expert 2800 points

    Hello John,

    Thank you for your answer, but I still have a few questions to ask. Please take the time to answer.

    As we know, the Vcc voltage is provided by the auxiliary winding, the voltage will be unstable at 12V.
    1. At full load the Vcc voltage maybe increases from 12V to 14V, the current into Icomp pin will become about 9uA, it will impact the function?
    2. What is the maximum range of this current?
    3. If the designer designs Vcc to be 15V at no load, does it mean that the resistance of Vcc to Icomp needs to be adjusted?
    4. Whether adding this 1.5M resistor will only solve the noise problem, will not affect other functions?

    Hope and waiting for you reply, thank you.

    Best regards.

    Rock Shao

  • 0 in reply to Rock Shao
    TI__Mastermind 34465 points

    Hello Rock,

    You need a fixed value of VCC for this or any other pfc application.
    If your bias voltage is changing a lot then you can use a simple linear regulator to stabilise the value.

    Regards

    John

  • 0 in reply to John Griffin1
    Expert 2800 points

    Hello John,

    In the Vcc voltage may have ripple about 2V~3V deviation whether it is powered by AUX or standby power, our customer will not use LDO because of the price,

    so they consider the Icomp if more the 7uA or too much will affect the full load? Whether adding this resistance will affect other functions?

    Hope and waiting for your reply, thank you.

    Best regards

    Rock Shao

  • 0 in reply to Rock Shao
    TI__Mastermind 34465 points

    Hello  Rock,

    You should check it out and see what happens.
    It may meet your product design requirements.
    However I recommend that you improve the regulation on Vcc