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UCC28950: ucc28950 output ossiclation

Part Number: UCC28950


I am designing a PSFB with 250V input 82v output power, I have made similar designs before but I am encountering a new problem, the output voltage of the power circuit oscillates around 1v when there is no load Tue.

but even when there is a 5w load, this situation disappears, so what is the reason for this situation?.

  • Hello,

    Your inquiry is under review.


  • Hello,

    There are many things that can cause your loop to oscillate.

    1. Feedback loop does not have enough phase margin

    2. Current sensing is not setup correctly

    3. Transformer turns ratio is incorrect

    4. To much slope compensation

    The following link will bring you to an application note that goes through the step by step design process of a phase shifted full bridge using the UCC28950.

    There is also a link inside the tool to an excel design file.  You can use both of these tools to review and check your design.


  • Hello, first of all, thank you for your answer.

    When the circuit reaches a certain temperature, the output oscillation that occurs during idle operation disappears and works correctly until it cools down again

    In this case, it first makes me think that there is a problem with the current transformer, but I changed it 3 times, the same situation continued, my question is how can the transformer I disconnected from another working circuit cause this situation ?

    Best regards

  • Hello,

    The current sense transformer may not be bad.  It is the placement of it and that it may not be resetting.  Try moving it to the input of the HBridge and setting it up per the app tool and note to see if you get better behaivor.