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UCC28610: Transformer and Snubber Design Issue

amol gupta59
Prodigy 60 points
Part Number: UCC28610
Other Parts Discussed in Thread: UCC28050

Hello there, i am using UCC28610 for constant voltage AC/DC conversion. Below are the specification

Output - 30Vdc @1.5A

Aux o/p - ~16V @ 100mA(for VDD)

I/P - 85Vac - 305Vac

Problem we are facing is-

1. Suggested Snubber(by UCC28610 design calculator) we are using gets burnt as soon as we turn on the circuit, though we still gets the output.

2. Currently PF is 0.65, Required PF is >=0.95.

3. Ithd = 109% & Vthd = 4.4%

Folks, would request you to kindly suggest the design and specification of transformer and snubber. 

P.S. - please share in depth specification of transformer with all parameters required to manufacture if possible as i only have elementary knowledge of it.

  • 0
    TI__Expert 7395 points

    Amol,

    Thanks for your interest here.

    To focus on the snubber first-have you tested at lower

    AC input voltage to see how high the MOSFET drain voltage is ringing to?

    Can you share your design details on the snubber?

    Have you tested the leakage inductance on your transformers?

    You can do that by shorting the secondary windings together and measuring the primary side inductance.

    Regards

    John

  • 0 in reply to John Stevens
    Prodigy 60 points

    Hello Sir,

    To focus on the snubber first-have you tested at lower AC input voltage to see how high the MOSFET drain voltage is ringing to?

    - by placing the the suggested snubber, Rsnub2 gets burn out as soon as i switch on, so it is not possible to take reading.

    Can you share your design details on the snubber?

    - Kindly find attachment. Here we are shorting pin 2 and 3 of p10 and RC snubber is in role.

    Have you tested the leakage inductance on your transformers? 

    - Our transformer primary inductance is 183uH and leakage inductance is 40uH (tested as per your suggestion).

    thanks

    Regards

    Amol

  • 0 in reply to amol gupta59
    TI__Intellectual 880 points
    Hello Amol,

    The first thing I noticed from your reply is your leakage inductance. Typically, the leakage inductance for flyback transformers are about 2% and under of the primary magnetizing inductance. The percentage of the transformer you mentioned is about 22%, which is quitehigh.

    Because of this high leakage inductance, there will be a large energy dump from the inductor into the snubber circuit, and may be leading to the burnt resistors.

    This is a PDF which a contact list for magnetic manufacturers that you can talk to and have a transformer built: e2e.ti.com/.../4010.Magnetic-Manufacturer-List.pdf

    You will have to provide information such as turns ratios, peak primary currents, primary inductance required to get a transformer made.

    Regards,
    Davit
  • 0 in reply to DavitKhudaverdyan
    Prodigy 60 points
    Hi Davit, thanks for the reply, would like to share that i have made certain inprovement in tansformer design and reached a state where snubber is not burning, but would like to know that how relaible is UCC28610 calculator; if i provide transformer specifation from that, will that be fine as there were certain value suggested for resistors which were not working as per calculator. Also, would be thankful if you can suggest how to improve PF, as it is only 0.6 as of now. thanks
  • 0 in reply to amol gupta59
    TI__Intellectual 880 points
    Hey Amol,

    I'm glad that your snubber is not burning anymore!

    The calculator tools are definitely helpful, and are there to help start designs and guide users along the way on component value selection. They are not a way to guarantee operation of the device as the calculators can make some assumptions, therefore the user has to do their due diligence to ensure things are correct.

    To improve PF, a PFC device can be used like the UCC28050, a transition mode PFC controller, which can be configured as a single-stage PFC and Flyback controller with an opto-coupler feedback network: www.ti.com/.../PMP11155

    Regards,
    Davit
  • 0 in reply to DavitKhudaverdyan
    Prodigy 60 points
    Hi Davit, Would like to correct myself, the leakage inductance of transformer is 6.7uH.
  • 0 in reply to amol gupta59
    TI__Intellectual 880 points

    Amol,

    That's great that you are able to get the leakage inductance lower.

    Are you still facing issues with the snubber network?

    Davit

  • 0 in reply to DavitKhudaverdyan
    Prodigy 60 points

    Dear Davit, i belive we have solved the issue of snubber. Can you help me with the power factor thing ? so far we have attained 0.730 PF at 230Vac. Can we use any #TI
    #PFC solution with #UCC28610 which can help us reach >0.95PF. Thanks