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UCC28722: Is it possible Output voltage change about UCC28722 in TIDA-00628 Design?

Bob Lee62837
Mastermind 7230 points
Part Number: UCC28722
Other Parts Discussed in Thread: TIDA-00628, UCC28720

Dear support member,
My customer will use UCC28722.

Althought output voltage is 15V in the TIDA-00628 design,
Is possible with Output voltage 5V, Iout current 1.4A in this design?

Specification condition
Input Voltage：80V AC～240V AC
Output Voltage：5.3V DC
Output Current ：1.2A
Non - Isolated

Design number：TIDA-00628
www.ti.com/.../TIDA-00628


Is this design possible?


Best regard.
Bob Lee.

  • 0
    TI__Expert 7395 points
    Bob,

    Thanks for your interest here. You can always search reference designs at ti.com/powerlab. I found this one that looks much closer to your requirement:
    http://www.ti.com/tool/pmp4372
    This design uses UCC28720 which is very similar to UCC28722 but has integrated HV startup for faster startup and lower standby power.
    Would that approach work ok or was there something about the design you were looking at that you really needed?

    Let me know if you have other questions.
    Regards,
    John
  • 0 in reply to John Stevens
    Mastermind 7230 points

    Dear John Stevens,

    Thank you very much for reply.


    Although you teached me pmp4372 design,
    pmp4372 design is using auxiliary winding.

    Without using auxiliary winding like TIDA-00628 design,
    I want to feed back to VS from the output side.

    Is this design possible?

    Specification condition
    Input Voltage：80V AC～240V AC
    Output Voltage：5.3V DC
    Output Current ：1.2A
    Non - Isolated


    If it is design possible,
    Could you teach the change from TIDA-00628?


    Very urgent.


    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    TI__Expert 7395 points
    Bob,
    Ok; I understand now. You can use the powerstage components from the PMP4372 (like BJT, input/output caps, output diode, etc.) but will just need to change the connections and the transformer. you should use a transformer with the same Np:Ns and primary magnetizing inductance but will just need to specify to the magnetics vendor to only have those windings and no aux winding. Vs resistors will need to be modified as well since they will be connected to the Nsec.
    You can use the excel design calculator in the UCC28722 tools folder here to set the Vs resistors (say that your Na is same turns as Ns just for the calculation).
    Regards,
    John
  • 0 in reply to John Stevens
    Mastermind 7230 points

    Dear John Stevens,


    Thank you very much for quickly response.

    I understood that powerstage components and transformer change.


    May I ask add a question?

    I think that the UCC28722 samples the VS waveform and is output voltage reguraltioned,
    Is it possible to think of the Vs waveform as a transformer voltage waveform on the secondary side?

    Is there a problem?

    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    TI__Expert 7395 points

    Bob,

    Yes sampling of Vs is how Vout is regulated. Usually the aux winding and Vs is a representing Of the output winding and voltage and the waveforms are basically the same besides perhaps differences in turns.

    Let me know if that answers you last questions here.

    Regards

    John

  • 0 in reply to John Stevens
    Mastermind 7230 points

    Dear John Stevens,

    Thank you very much for reply.
    I understood about waveforms are basically the same.


    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    Mastermind 7230 points

    Dear John Stevens,


    I have two question.


    The design of TIDA - 00628 has no auxiliary winding,
    As the specification of this time we are considering the VDD voltage with the 15V voltage of the secondary side as 5V voltage.


    Q1.
    Although the UVLO of the rising voltage of VDD is 21 V,
    will the IC start up even if this 5 V voltage on the secondary side is applied?


    Q2,
    Since the current flows at the start of the IC,
    does the loss of R4 and R5 of TIDA - 00628 design become large?

    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    TI__Intellectual 880 points

    Hello Bob,

    About Q1: 

    The IC will not start unless it has reached its turn on UVLO of 21V. After that, operation is guaranteed until the device hits the abs max UVLO turn off value 8.3V, after that the IC will turn off. Because 5V is below the UVLO threshold, the IC will not turn on. 

    About Q2:

    The startup resistors can be a lossy source, depending on the input voltage and resistor selection. To calculate the power loss of the startup resistors use the equation Ploss = V^2/R, where V is the bulk voltage and R is the resistance of the startup resistors. 

    If you find the loss from the startup resistors to be too much, the UCC28720 is the same part but with a dedicated high voltage startup. 

    Regards,

      Davit

  • 0 in reply to DavitKhudaverdyan
    Mastermind 7230 points

    Dear DavitKhudaverdyan,

    Thank you very much for reply.

    Best regard.
    Bob Lee.