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Original question:

UCC28056: Schematic review

UCC28056: UCC28056 has low efficiency and abnormal inductive current spikes

Gabriel Wang1
Genius 3825 points
Other Parts Discussed in Thread: UCC28056

Dear Expert 

Could you give some advice how to reduce the pfc inductor spikes and imporve efficiency .

The customer outputs 100W and 20V5A from the ready-made solution of the existing model, but changes the power supply structure. It is found that the UCC28056 efficiency is reduced from 90.3 to 89.3 points in full load, and the same problem also exists in half load.By measuring the PFC inductance current waveform, there is an abnormal spike relative to the previous mature scheme.

PFC inductor current waveform:

2. By looking at the driving waveform and comparing the inductive current waveform, it is found that there are driving waveforms and large and small waves:

  • +1
    TI__Genius 9140 points

    Hi Gabriel:

    is this an adapter application and can I know for which customer?

    the current spike during mosfet off moment usually is caused by charging parasitic cap on the mosfet Drain  from 0V to 400V. Please try to check whether the parasitic cap is from PFC inductor or PFC boost diode.

    for the unstable pulse, usually it is relate to the ZCD sampling, so layout for ZCD pin is important.

    you can refer to my email since adapter is important customer for us. We can support you through email. 

    Wenbin-huang@ti.com