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UCC28180: PF Drop and Current Peaking in UCC28180-Based CCM PFC at High Load

Sourov Roy
Prodigy 20 points
Part Number: UCC28180

Tool/software:

Dear TI Community,

I am currently working on a 1000 W Continuous Conduction Mode (CCM) boost PFC design using the UCC28180 controller. The circuit performs well at light to medium loads, maintaining a power factor (PF) of 0.99 up to approximately 700 W. However, as the output load increases beyond 750 W, I observe a gradual drop in PF to around 0.95.

Upon probing the waveforms with an oscilloscope, I noticed that both the inductor and input current waveforms begin to show peaking near the AC line voltage peaks. This distortion seems to coincide with the observed drop in PF.

To support this observation, I have captured and arranged waveforms chronologically at increasing output loads of 1.9 A and 2.25 A.

Key design parameters:

  • Vin: 180–265 VAC, 50/60 Hz

  • Vout: 350 VDC

  • Pout: 1000 W

  • Rsense: 250 mΩ

  • Boost Inductance: 410 µH at nominal current

  • Switching Frequency: 100 kHz

I would appreciate any insights, recommendations, or reference material to help me better understand and address this behavior, particularly regarding waveform distortion and current shaping near full load.

Thank you in advance for your time and support.

Best regards,
Sourov Roy

Iout=1.9A

Iout=2.25A



  • 0
    TI__Prodigy 160 points

    Hi Sourov,

    As the load increases, the ICOMP voltage also increases. If the ICOMP voltage hits the upper limit of 6V, this situation can occur. Please check the ICOMP pin voltage to confirm that. And if this is the case, then reduction in the Rsense resistor by half should solve this problem.

    Regards,

    Soumya

  • 0
    Prodigy 20 points

    Hello Soumya,

    Thank you for your suggestion. I am a bit cautious about reducing the Rsense value by half, as a lower voltage across Rsense could compromise noise immunity.

    Could you please explain how the Rsense value mathematically correlates with the ICOMP voltage in this control architecture?

    Thank you,
    Sourov Roy

  • 0 in reply to Sourov Roy
    TI__Prodigy 160 points

    Hi Sourov,

    Please check the following highlighted statement in the UCC28180 datasheet:

    At higher Rsense the sensed value of inductor current is higher and ICOMP voltage tries to get adjusted to that higher value. Then if the load also increases, the inductor current also needs to increase causing the ICOMP to increase and eventually it gets clamped to the maximum value (6V). That is why if a lower Rsense is used, at same loading condition the sensed inductor current would be less and the ICOMP voltage also would be lesser.

    Regards,

    Soumya