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ucc28070/ non identical inductor currents

Dimit Ariti
Prodigy 110 points
Other Parts Discussed in Thread: UCC28070

Hi

I've designed a 1.2kW PFC universal input 400 V output with UCC28070. When I apply 100rms input to the prototype the voltage look regulated but the problem is in inductor current of phase 1. This is an  interleaved topology and 2 phases are exactly identical; Same inductor, same Mosfet , current controllers and sensors (CT) and other parts all the same. But the indcutor current for phase 1  is different from 2 in a bad way. I have uploaded the picture here. Inductor 2 look very good but indcutor current 1 looks distorted with more distortion at zero crossing. I know the reason for zero crossing issue is negative current and very low input and very light  power and I checked the inductor current for phase one  and it is indeed  negative  around zero crossing area but inductor in phase 2 doesn't have any negative current in the same area. And I know I can add the proposed dc offset circuit in UCC28070 datasheet to solve the issue. But why my other phase doesn't have these issues? Other than the zero crossing issue there a overshoot in current of L1 as can be seen in picture.I was able to smooth this overshoot by changing current controller but not the zero crossing issue.. The question is  why I don not have this problem in phase 2 that has exactly the same current loop controller? I even swap the inductors in phase 1 and  2 and it did not help.

Thanks

  • 0
    TI__Mastermind 40120 points

    Hello SKN96,

    I will route your issue to the appropriate team to address this issue.

    You mention the problem is with L1 current, but the screen shot with distorted current is labeled IL2.  I presume this is just a typo.  Until the other team responds, let me suggest that you investigate the current-amplifier output for the affected phase.  It appears that the CAO output is spending extended time at zero and then snaps to the regulation point with an overshoot. 

    Even if the two phase circuits are designed identically on paper, the actual prototype may have a bad component or mis-wiring or something to affect only that node.  Please check to see how the output of the affected CAO differs from that of the normal CAO.  If the output components are all okay, then check the inputs of those CAOs to try to trace back the differences to the ultimate cause of the problem.  

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    Prodigy 110 points
    Hi
    Thanks for your feedback. I did exactly the same thing as you suggested and I think I found the rout cause. While all the component were identical for two phases but the current feedback trace on the the problematic phase was thinner . I fixed this issue and now both phases current look identical. Thanks.