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UCC28740: The switch frequency for UCC28740

Zhang Liang
Genius 4205 points
Part Number: UCC28740

Tool/software:

Hi,

I have submitted the issue in the other thread and you suggest us to use the ucc28740 design calculator, please refer to below and provide your comment if there are any paramater need to modify.

BTW, please advise if there are any transformer paramater suggestion that we can customize from our supplier? thanks.

The previous E2E link: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1476867/ucc28740-the-auxiliary-power-supply-design-issue-for-ucc28740/5670914#5670914

1602.sluc487b.xlsx

2768.PQ3220P12M420U.pdf

  • 0
    TI__Guru* 86286 points

    Hello,

     

    Your inquiry will be reviewed in the order it was received.

     

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 86286 points

    Hello,

     

    Thankyou for providing the previous link. 

     

    I reviewed the excel tool it recommended that you use a turns ratio of 9.5 for Nps and used 6.  This means the design is going to operate in DCM and at lower frequency.   This agrees with the current behavior in your design.

     

    The design tool also suggested a primary magnetizing inductance of 308 uH roughly.  You used 420 uH which drive the operating frequency down even further.   This agrees with the current behavior in your design.

     

    When it comes to using this tool, I would recommend you select transformer turns ratio’s and transformer primary magnetizing inductances within +/- 5%. of what the tool recommends.  In most cases you will need a custom transformer for your application.  I have used Wurth and GCI in the past to design transformers for me.

     

     

    If you select the transformer as the tool suggests it will operate at critical conduction at max load min line and at 80 kHz or greater. 

    Thank you for interest in Texas Instruments (TI) products.  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.

     

    Regards,