• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 237 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

PFCLLCSREVM034: Regarding the resonant inductor and resonant capacitor in the LLC stage and leakage inductor of the transformer

Sean Hung
Prodigy 60 points
Part Number: PFCLLCSREVM034
Other Parts Discussed in Thread: UCC256404, UCC25640EVM-020

Dear Sir/Madam,

I have purchased and tested the evaluation board PFCLLCSREVM034, its performance is very good. After reading the user guide and datasheet of the UCC256404 and using the design tool UCC25640x Design Calculator Rev4.0, I have some questions regarding the resonant capacitor and resonant inductor and I hope you can give me some advices.

1) According the design procedure in the datasheet and the UCC25640x Design Calculator Rev4.0, I know the resonant capacitor value is 0.030uF = 30nF. But I can't find this capacitor in the circuit. Maybe this resonant capacitor consists of many capacitors connected in parallel or series? Could you identify it for me? My reference is schematic of PFCLLCSREVM034.

2) The detailed information of transformer is not listed in the user guide. The only information I got from schematic is turn ratio = 33:3:2:2 and LM=510uH. I can't find out the value of leakage inductor. This is another question in the point 3 below.

3) Regarding the resonant inductor. I would like to know should we consider about the leakage inductor of transformer? For example, if the calculated resonant inductor is 100uH, and the leakage inductor of the transformer is 20uH, should I use a 80uH inductor or still a 100uH inductor?

Thank you for your answer.

  • +1
    TI__Genius 12875 points

    Hi Sean,

    Thanks for reaching out to us.

    Please find the responses to your questions below: 

    Sean Hung said:
    1) According the design procedure in the datasheet and the UCC25640x Design Calculator Rev4.0, I know the resonant capacitor value is 0.030uF = 30nF. But I can't find this capacitor in the circuit. Maybe this resonant capacitor consists of many capacitors connected in parallel or series? Could you identify it for me? My reference is schematic of PFCLLCSREVM034.

    1. The design calculator values given in https://www.ti.com/lit/zip/sluc675 referring to the standalone EVM given in https://www.ti.com/lit/pdf/sluubx3, not the PFCLLCSREVM034. That's the reason you don't find the capacitor of 0.03uF in the PFCLLCSREVM034 schematic. Both of these EVMs power ratings are different. So, their design will be different.

    Sean Hung said:
    2) The detailed information of transformer is not listed in the user guide. The only information I got from schematic is turn ratio = 33:3:2:2 and LM=510uH. I can't find out the value of leakage inductor. This is another question in the point 3 below.

    Please find the Lr value below. As I mentioned, this is taken from the standalone EVM user guide (https://www.ti.com/lit/pdf/sluubx3).

    Sean Hung said:
    3) Regarding the resonant inductor. I would like to know should we consider about the leakage inductor of transformer? For example, if the calculated resonant inductor is 100uH, and the leakage inductor of the transformer is 20uH, should I use a 80uH inductor or still a 100uH inductor?

    Design calculator will find those inductor values for you. You just need to select the either the discrete solution or the integrated solution in the design calculator (please see the second screen shot below). 

    Please let me know if you have any further questions.

    Regards

    Manikanta P

  • 0 in reply to Manikanta Pallantla
    Prodigy 60 points

    Hi Manikanta,

    Thank you for answering my questions. It is very clear, detailed and helpful!

    Now I would like to double some questions.

    1) According to your answer 2, the schematic of UCC25640EVM-020, the resonant capacitor is combined by C1+C17=0.03uF=30nF. So I think the resonant capacitor of  PFCLLCSREVM034 (30nF) consists of C2, C13, C45 and C46 (0.01uF+0.01uF+4700pF+4700pF=29.4nF)? Am I right? 

    2) I already know that I can select discrete inductor or leakage inductor to form a resonant inductor in the calculator. Then I would like to ask more detail question. will transformer become too hot or decrease efficiency if I use the leakage inductor as resonant inductor? In my project (150W PFC+LLC, power density target is 40W/in3), the product size is limited so it is very helpful to reduce a discrete component for saving space. However, due to the limited product size, efficiency is also an important topic to reduce heat. Based on this condition, do you recommend to use discrete inductor or leakage inductor?

    Thank you very much for the help.

  • +1 in reply to Sean Hung
    TI__Genius 12875 points

    Hi Sean,

    Please find the answers below:

    Sean Hung said:
    1) According to your answer 2, the schematic of UCC25640EVM-020, the resonant capacitor is combined by C1+C17=0.03uF=30nF. So I think the resonant capacitor of  PFCLLCSREVM034 (30nF) consists of C2, C13, C45 and C46 (0.01uF+0.01uF+4700pF+4700pF=29.4nF)? Am I right? 

    1. You are correct. Effective resonant capacitor value is 29.4nF.

    Sean Hung said:
    2) I already know that I can select discrete inductor or leakage inductor to form a resonant inductor in the calculator. Then I would like to ask more detail question. will transformer become too hot or decrease efficiency if I use the leakage inductor as resonant inductor? In my project (150W PFC+LLC, power density target is 40W/in3), the product size is limited so it is very helpful to reduce a discrete component for saving space. However, due to the limited product size, efficiency is also an important topic to reduce heat. Based on this condition, do you recommend to use discrete inductor or leakage inductor?

    2. I would suggest to go with integrated magnetics since density is a main criteria here. Efficiency and heat generation depends on how you design the transformer. You can always optimize by considering proper core and wire size. 

    Regards

    Manikanta P

  • 0 in reply to Manikanta Pallantla
    Prodigy 60 points

    Hi Manikanta,

    Thank you very much for your answering. it is very helpful. I have idea how to do now. I will update my design to see if the performance can be improved.

    Regards,