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UCC28070: Setting Up Peak Current Limiting (RPK1, RPK2)

Lawrence He
Genius 3280 points
Part Number: UCC28070

Dears,

I was refer (UCC28070 300-W Interleaved PFC Pre-Regulator Design)

The UCC28070 has an adjustable peak current limit comparator that can be set up by selecting R PK1 and calculating the required R PK2 . For this design to keep the reset voltage of the current sense transforme manageable the peak current sense signal (V S )

my customer want to change the R28 ( PPK 1) to 1.8k ohm from 3.65k ohm.

this change impact voltage level from 3.7v to 4.59v of peak current limit and have any side effect for this peak current limit change?

 

If any, Please advise me.

 

Thanks,

 

Best regards,

 

Lawrence.

  • 0
    TI__Mastermind 31580 points
    Hi Lawrence,

    Let me take a look at this for you, I hope to have a response to you within a day.

    Regards

    Peter
  • 0 in reply to Peter Meaney
    Genius 3280 points

    Hi, Peter

    Thank you for your reply,  our client have tested input AC Drop in this case as attachment.CH-1280AR PFC OUT ID AC Drop test 20170712_Eng.pdf

    our client find the question , If AC input source drop from 100v to 91v, the Gate B PWM will get chaos, and two phase can not balance, but if R28 ( PPK 1) to 1.8k ohm from 3.65k ohm , Gate B PWM goes normal.

    Why thus solution can fix this problem, and what is the side effect of this solution.

    Thanks,

    Best regards,

    Lawrence.

  • 0 in reply to Lawrence He
    TI__Mastermind 31580 points
    Hi Lawrence,

    When the AC input is dropped from 100V to 91V the AC line current will increase and it looks like that with R28 at 3.65k the peak current is hitting the PKLMT threshold. Changing R28 to 1.8k raises the PKLMT.

    Raising the PKLMT increases the peak current that can flow in the PFC inductor, so its is important to check for signs of saturation at lowest input voltage and worse case load just before the current in the inductor hits the PKLMT value.

    Regards

    Peter