This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Question about Reference design schematic of UCC28880

Guru 19475 points
Other Parts Discussed in Thread: PMP10143, PMP10765, TL431, UCC28880

Please let me know about mean of external components for PMP10765 and PMP10143 below.

①About noise filter, why difference capacitor value?

 (PMP10765 is 1mH/6.8μH/6.8μH, but PMP10143 is 1mH/4.7μH/4.7μH)

 Is there calculation method?

②About PMP10765 schematic, what mean of D4?

I think that D1 is reverse protection, but I don't understand mean of D4.

③About PMP10765 schematic, what mean of R3 and R101?

Best regards,

Satoshi

  • Satoshi-san

    1. PMP10765 is slightly higher power, and it is half-wave rectified instead of full-wave rectified, so it needs more bulk capacitance for energy storage, to minimise the voltage ripple on the bulk caps.

    2. For PMP10765, D1 & D4 are half-wave rectifying diodes for the AC input, whereas PMP10143 is full-wave rectified and uses 4 diodes D3, D4, D7, D8. Hal-wave rectification could be done with a single diode D1 (D4 could be short-circuited), but having 2 diodes gives higher voltage stress capability (for lightning surge transients etc), could allow 2 lower voltage diode to be used, and may give an EMI benefit for common-mode since the structure is balanced compared to using just a single diode.

    3. R3 & R101 are required to ensure there is some minimum load at output no-load condition, to limit the rise of Vout at no-load. This is explained on page 26 of the datasheet. There is a trade-off between matching the RC time constant of the output cap + R3/R101/Rload vs. the feedback time constant R1/R2/C2. PMP10143 uses opto feedback, so the bias current for the TL431 + various resistors will provide a min load on the 3V3 rail, while the 12 V rail uses a zener D2 to limit to the no-load output voltage.


    I hope this answers your questions, if so please click the "verify answer" button.

    Thanks,
    Bernard
  • Bernard-san

    Thank you for reply,
    Sorry for additional question about your answer 2.
    If the circuit using PFC, isn't UCC28880 need to use D1 and D4?
    ※PFC output to UCC28880 Vin(HVIN)

    Best regards,
    Satoshi
  • Satoshi-san,

    If I understand your question correctly, are you asking if D1 & D4 are not needed if the UCC28880 is connected to the DC bus output voltage of a PFC circuit?

    If so, then yes you are correct - if the input voltage to the UCC28880 is DC, then rectifying diodes D1 & D4 are not required - they are only needed for AC input.


    I hope this answers your questions, if so please click the "verify answer" button.

    Thanks,
    Bernard
  • Bernard-san

    Thank you for very quick answer.
    Your understand is correct.

    Best regards,
    Satoshi