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2KW PFC UCC28019 Inductor Current

Danel October Beriong
Prodigy 240 points
Other Parts Discussed in Thread: UCC28019, UCC28070, UCC28061, UCC28051

Hello! It's me again. I was just wondering what's going on with my 2KW PFC circuit using ucc28019. I was finally able to make it work, I put a small load on it, it outputs a more or less steady 385Vdc, at 0.8A. The problem I'm seeing is the inductor current, whose waveform is attached here. I was wondering where the spikes near the peak are coming from? From the zero crossing it's quite steadily rising, and then as it nears the top it goes crazy. My superior says it has something to do with over compensation? Or the fact that I'm not using the rated load of (supposedly) 2KW. Please advise. Thank you very much! (I'm attaching the latest schematic after this post)

  • 0
    Prodigy 240 points

    Here's my latest schematic for a 2KW PFC:

  • 0 in reply to Danel October Beriong
    Expert 1920 points

    Note: Often in PFCs (UCC28051, UCC28061 and UCC28070) your ratio of resistors for VINS and VSENSE have to be the same.

  • 0 in reply to CWilson
    TI__Genius 15910 points

    Please send a more close-up view of the waveform where the issue is occurring.  Also, scope images of the VCOMP, VSENSE, ISENSE, and GATE would help.

    What is the circuit doing at higher load?

  • 0 in reply to Lisa Dinwoodie
    Prodigy 240 points

    I'm still reluctant to try higher loads due to the mosfet explosion at 990W when I first finished the circuit. I was foolish enough not to observe the low load behaviors of the different components of the circuit before increasing the load. That's why I'm being really cautious this time around. Hehe. Anyway, I'm attaching waveforms of the inductor current and the gate voltage with a 300W load:

    This was taken at around the peak of the line voltage (230VAC). As you can see, the gate voltage duty cycle alternates between about two values. I'm not sure about the inductor current but I think it has saturated at the points where the duty cycle is greater.

    My next post will show the waveforms for a lower load.

  • 0 in reply to Danel October Beriong
    Prodigy 240 points

    This next set of waveforms is still from the inductor current and gate voltage. Notice the almost uniform pattern.

    My superior is suggesting that this has something to do with the Vcomp circuit not "tuned" to higher loads, that it's "hunting" for the target but can't quite reach it: it's either over or under compensating. Or maybe I just need a bigger inductor? By the way, I'm using an ETD59 ferrite core, with 9 turns. Is that enough, or should I go for bigger inductors? The highest PFC rating I've seen that people have actually built is 1.7kW. I don't have that many references right now that's why I'm bugging you guys.. hehe. Thanks for the replies!

  • 0 in reply to Danel October Beriong
    Expert 1920 points

    Looks nice at lower loads.

    What is your inductance and your air gap in the core? 9 turns is not much, but it depends on material.

    It looks like you don't have a air gap given your number of turn. Correct?

  • 0 in reply to Danel October Beriong
    Expert 1920 points

    Looks like saturation.

  • 0 in reply to CWilson
    Prodigy 240 points

    Yes, I'm trying out the inductor with NO gap. If I put in an air gap, like 1mm, i would need about 34 turns. But with my power requirement, I think it will no longer fit in an ETD-59 core. Is my assessment correct? If so, what inductor cores would you suggest for a 2.2kW PFC?

  • 0 in reply to Danel October Beriong
    Expert 1920 points

    If you don't use air gap it's difficult to control the inductance over the whole load range and temperature!

    It's recommended to use an airgap.

    I think it's possible with a ETD59, but you have to do some calculations regarding you transformer. Try to see the calculations for UCC28070.

    Nboost = (L*lpeak) / (Bmax * Ae)

    Bmax = 0.25, Ae = 368*10^-6

    Round the number to nearest number which is large. Eg. if 13.4 then choose 14.

    Airgap:

    lg = (Nboost^2 *4*Pi*10^-7*Ae) / (L)