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UCC28180: improve PF at low load.

Constantin Bierschenk
Prodigy 40 points
Part Number: UCC28180

Hello,

i want to use the ucc28180 controller for my pfc. The informations About the PFC are:

-Vin= 90-130 VAC at 330-800Hz

-Vin_nrom= 115 VAC at 330-800Hz

f_sw = 250kHz

Vout= 350V

Pout= 105W

For the design i used the desing calculator and tested it on the UCC28180EVM-573. The IC works but the PF is not very well. 

So my Problem is to improve the PF at low load. I measure a PF at about 20 W of 0.66 and at 50W of 0.88. The target is a PF of 0.95 at 50W and a higher PF at 20W.

The only difference to the calculations is, i used a Little bit higher inductor value.

So what can i Change to improve my PF.

Best regards 

  • 0
    TI__Mastermind 34465 points
    Hello Constantin,
    The UCC28180 has been designed for 50/60Hz applications and so most of the reference designs and knowledge gained from actual product design has been learnt from these lower frequency products.
    Some testing has been done with this part in the aircraft power 115Vac,400hHz nominal input application but the data obtained is limited .
    I don't know what changes you made to the EVM but you will need to
    (1) increase the value of current sense resistor
    (2) decrease the high voltage cap on the DC side of the bridge
    (3) Increase the loop bandwidth from about 10Hz to 60Hz.
    (4) Increase the boost inductance

    All CCM pfc power supplies suffer from a loss of pf at light load. This is because the current is no longer continuous at lighter loads and so the equations used for controlling the current are no longer correct.
    Additionally with the UCC28180 the voltage used to sense the load current becomes very small and is subject to noise picup in the high voltage switching environment.
    When you increase the line frequency to 400Hz you will get and increased zero crossing distortion due to the increased phase lead time.
    The increased harmonic distortion is discussed in this reference:
    e2e.ti.com/.../507259

    Regards
    John
  • 0 in reply to John Griffin1
    Prodigy 40 points

    Hello John,

    thanks for the helpful answer.

    I changed every step except step 3.Step 3 was a good hint and helped me to improve my PF. Moreover after i change the caps at the pi input-filter (decrease to 100nF) i reached a PF of 0.98 at 50 W load.

    Very good help. Thanks a a lot for the good hints.

    Best regards