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UCC28951-Q1: Vibration of input current

HEIJI KANEDA
Prodigy 60 points
Part Number: UCC28951-Q1
Other Parts Discussed in Thread: UCC28951, UCC28950

Dear E2E.

Good day

I'm having problems with a full bridge converter using UCC28951.
Please tell me how to deal with it.

The input current of the transformer is vibrating. 

What is the cause?

Regards,
Kaneda.
 
  • +1
    TI__Guru* 86266 points

    Hello,

    The design seems to have major jumps in duty cycle.  You might want to study the comp , CS and input voltage of the design and input voltage of the transformer.

    It could be one of two things.

    1. CS signal could be too noisy  which an RC filter at the CS pin should resolve.  1k and 220 pf in low pass filter may help.

    2. Loop stability issue

    >The following application note has information on designing with the UCC28950 and UCC28951 and has a section on loop compensation.

    www.ti.com/.../slua560c.pdf

    3. Layout issue

    >Section 10.1 and 10.2 in the data sheet give tips on how to layout the PSFB controller.  These tips should help you double check your design.

    It also may be helpful  to order and evaluate the UCC28951  EVM to evaluate.  You can find information on this at the following link.

    www.ti.com/.../sluubj5

    Regards,

     

  • +1
    Prodigy 210 points

    Looks like loop gain to high @ Fs/5 and sub harmonic oscillating. I had same/similar problem and changing comp pole lower slightly fixed the issue