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WEBENCH® Tools/UC3844: Webbench design alert

vinod sharma
Intellectual 420 points
Part Number: UC3844

Tool/software: WEBENCH® Design Tools

Hi,

We are trying to simulate below isolated power supply in web-bench.

Input: 20-28 VDC

Output: 90VDC/1.25Amp CC/CV isolated

Webbench generate the circuit using UC3844AN &  gives below error.

Please tell why this error is coming. Will UC3844 be OK for this requirement. We need highest efficiency.

regards

Vinod Sharma

  • 0
    TI__Expert 3095 points
    Hi Vinod Sharma,
    It sounds like the MOSFET you are using may not be suitable for the application.
    Please could you provide a few more details such as:
    1) The power topology you are using.
    2) The MOSFETs selected.
    3) The switching frequency selected.
    This information will help us to assist you.
    Thanks
    Joe Leisten
  • 0 in reply to Joe Leisten
    Intellectual 420 points

    HI,

    Please note that Junction temperature alert is for U1 (UC3844) not for the Mosfet.
    Please see requried detail as below:
    1) The power topology you are using. --> Based on my input webench suggested flyback. Please confirm is this OK?
    2) The MOSFETs selected.---> Ideal MOSFET is selected by webbench.
    **************************************************
    UC3844A Design
    With the current design condition, suitable FET could not be found in the current database. Hence, this design is created using an ideal FET.
    Please note that the resulting FET parameters are ideal, so the efficiency/loss values have been disabled. Also, the schematic/PCB export and
    Thermal simulations will not work with the ideal FET.
    *****************************************************
    3) The switching frequency selected. --> 100Khz selected by webbench.


    Please help to select best part considering high efficiency requirement for this design.

    regards
    Vinod Sharma

  • 0
    TI__Intellectual 1020 points

    Hi Vinod,

    Thanks for using WEBENCH, I checked this issue.
    Looks like this is a faulty error message regarding U1 Tj.

    In design conditions where we are not able to find a FET with proper part number from our database, WEBENCH still proposes the design but with an "Ideal FET", to help the user analyse the rest of the circuit.  In these cases, parameters like Efficiency, IC Tj, M1 Pd, M1 Tj are not calculated, as they will be dependant on actual FET selected.

    However we still give the rest of the WEBENCH design with other component parameters and other operating values like duty, loss in other components,etc.

    opvals.docx

    For now, you can ignore the warning message and try checking out the rest of the design. 

    We will fix the alert message issue for this device. 

    Feel free to let us know if anything

    Thanks
    sahil