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UCC28056EVM-296: EVM audible noise

Part Number: UCC28056EVM-296
Other Parts Discussed in Thread: UCC28056, UCC28051

Hi Team,

EVM audio noise comes out while VINAC up to 264V~280V, If want to avoid this, how can I adjust? 

Thank you.

  • Hi Chentsu,

    The EVM was rated to 264Vac maximum. This is beyond what the original EVM was designed to do. I would check the voltage ratings for the components in the AC filter. Also look at the HV pin and check if X cap discharge is continuously engaging.

    Best Regards,
    Ben Lough
  • Apologies, wrong post. For UCC28056EVM, 264V to 280V is still greater than what the original EVM was designed for. I would suspect there is not enough headroom between the peak of the AC line and the output voltage. At 280Vac, the peak of the AC line is 395V which is already bigger than the 390V output the boost converter was designed for. I would suggest raising the output voltage setting by a ~20V or so and also readjust the ZCD/CS pin divider.

    Best Regards,
    Ben Lough
  • Hi Chentsu,

    Does this issue require further attention?

    Best Regards,
    Ben Lough
  • Hi Ben,

    Here's a question. If customer needs 80VAC brown-in, then I set the voltage divider as 27.4KOhm and 3.24MOhm*3 for 0.282 minimum Brown-in voltage. But if use this value to calculate OVP2 by 1.102V~1.148V, the OVP voltage is around 400V, almost equal to bulk voltage.

    Is there any suggest for the question? Or Bulk voltage needs to be set to under some value?

    C.T.
  • Hi Chentsu,

    Thanks for the response. While UCC28056 can support universal type input ranges from 85Vac to 265Vac, if an application requires wider input voltage range than this (80Vac to 305V for example), UCC28051 would be a better fit.As you noted, the brown-in threshold of the ZCD/CS pin would limit the maximum allowable bulk voltage setting to avoid tripping OVP2 protection.

    Best Regards,

    Ben Lough