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UCC28740: ucc28740 in HV app

robin gangopadhya18
Mastermind 6050 points
Part Number: UCC28740
Other Parts Discussed in Thread: UCC256404, , UCC28782

Hello Jaden:

Problem!

I tried to massage the Lr. Cr, Lm values in the UCC256404 design calculation Spreadsheet but it seems there is no convenient practical values one can obtain in this topology with high turns ratio & low power.

I see Lr in 500uH range, Cr approx 1nF, Lm 3000uH....Then Vcr may be 3000V!

These values will not make a consumer /industrial grade module at a convenient price range.

So I got to take another look at UCC28740.

As you had suggested earlier.

I will post if I find a way to proceed with LLC given that I bought out  the Eval board, 100 PC of the controller etc!\LOL

We do have a project to make LLC modules...not right now.

Do you have some other controller? But for now, going to take another calculation for UCC28740. For input to 6500V, 5v output, 30-40W load.

Let us see where it goes from here.

Any help in this matter will be highly appreciated.

r

  • 0
    TI__Expert 3431 points

    Hi, Robin:

    Nice to meet you. I would like to clarify the input voltage specification since I saw you are looking a solution with 600V input. However, you mentioned 6500V input here. So is it different case or just typo?

    I think it is not good idea to transfer 6500V to 5V with a single flyback topology. The transfer losses would be very high of transformer. And it is needed to use >6500V switching components if input is 6500V. That would be also a challenge. 

    If you are looking for a flyback solution with 650V input voltage, UCC28740 is okay to use I think. 

    Regards, 

    Wesley

  • 0 in reply to Wesley Hsu
    Mastermind 6050 points

    Wesley:

    Ooops: how on Earth I TYPED 6500?

    TYPO FOR SURE.

    MAX INPUT IS 600v.

    Other than the depletion mode, we think UCC28782 is a better fit.

    I am proposing a series-connected depletion FETs.

    Can I send the circuit to you instead of in the forum?

    thnx

    -r

  • +1 in reply to robin gangopadhya18
    TI__Expert 3431 points

    Hi, Robin:

    Since this thread is for UCC28740 related questions, I saw you already created another thread to discuss about UCC28782. 

    Would you please reply and propose your idea in that thread? It helps us classify threads by different part. 

    Thanks. 

    Regards, 

    Wesley 

  • +1 in reply to Wesley Hsu
    Mastermind 6050 points

    Wesely:

    They deleted the chain with UCC2870X issues we were trying to resolve.

    we left it at the nature of Vrcs SHOWING THE Ipri pk. In trying to resolve why efficiency was dropping at higher inputs and why there were signs of "saturation".

    I think we have come to a root cause of it all: it is that the AUX  winding diode to get VDD bias was wrongly placed with much lower BVrev . As a result, that diode would start drawing higher and higher reverse current - leading to higher input current without adding anything to outputs.

    There were other side effect too:

    - in all that had wrong diode, it appeared xmfr saturating.

    - in all with wrong didoes, THIS DIODE WENT SHORT at higher inputs.

    In all correct assemblies, the current was strictly linear at all inputs and power.

    None of the modules with the correct diode showed any trouble, even showing 95% efficiency!

    We are in the midst of correcting this error.

    Hope this resolves it all.

    I will let you know.

  • 0 in reply to robin gangopadhya18
    TI__Expert 3431 points

    Hi, Robin:

    Glad to hear that you find the problem. Please let me know if you need any assistance. 

    btw, the UCC28712 thread is here. You can click it to find the previous post. 

    Regards, 

    Wesley

  • 0 in reply to Wesley Hsu
    Mastermind 6050 points

    Wesley:

    Since this module is high performance and very useful, we would like it evaluated by TI & mentioned in TI literature such Eval kits, How do I proceed?

  • 0 in reply to robin gangopadhya18
    TI__Expert 3431 points

    Hi, Robin:

    I think E2E is not the right window for this request since E2E is for technique discussion. I would like to suggest you to contact we TI local team for discussion first. I will ask our members if anyone know the process.

  • 0 in reply to Wesley Hsu
    TI__Expert 3431 points

    Hi, Robin:

    I am sorry that we have no this kind of process after I checked internally. Sorry about that. 

    Regards, 

    Wesley