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UCC28950: residual-current device jump

Eze Bayer
Prodigy 150 points
Part Number: UCC28950

Hello, I am testing the power supply based on UCC28950 and with isolated load it works perfectly with 25A@24V. But when I put the load referenced to ground, the ground fault circuit interrupter of the electrical installation of the laboratory jumps. My circuit looks like the reference design.

do you know how to solve it?

Thank you

  • 0
    TI__Guru* 85616 points

    Hello,

    When you ground the designs output to ground.  You could be compromising the designs isolation.  Try using an isolated power supply to power your UCC28950 design.  This should remove the fault.

    Regards,

       

  • 0 in reply to Mike O'
    Prodigy 150 points

    thanks for your reply. The system I feed is going to be referenced to ground, so such isolation is not necessary and the AC-DC that feeds my design is not isolated. Is there any other way to solve this problem?
    I do not understand what would solve having an isolated AC-DC if the DC-DC design is already isolated

    Regards

  • 0 in reply to Eze Bayer
    TI__Guru* 85616 points

    Hello,

    So when you ground the output of the design it is causing current to go where it should not.  You will have to track that down to see what it is going. 

    Try a resistive load on the output and see if the same issue occurs.  It may be your electronic load causing the issue.

    Regards,

  • 0 in reply to Mike O'
    Prodigy 150 points

    When i connect the output to a isolated load the circuit functions perfect. But not if I connect output negative with installation ground. This is my circuit: 

    "Cgnd" (in blue) is the only component that link primary with secondary. This could be the problem? why this is necesary?

    Regards

  • 0 in reply to Eze Bayer
    TI__Guru* 85616 points

    Hello,

    Not sure what you mean by installation ground.  Could you explain this further?

    The capacitor that you have from primary to secondary is generally used for EMI.  It works in conjunction with the transformer to form an EMI filter.  I have not seen any calculations for this but it is quite common.

    Did you ever try the resistive load I suggested when doing this test?  An electronic load is active and if it is isolated when connect it to earth ground it may misbehave.  I would still suggest trying this?

    Regards,

  • 0 in reply to Mike O'
    Prodigy 150 points

    Hello Mike, yes, I test with resistive load and it's ok.

    I attach a figure to clarify the measures and the problem

    I don't know why GFCI breacks the 220 supply, I don't know where is the leakage current and how to solve it

    Regards

  • 0 in reply to Eze Bayer
    TI__Guru* 85616 points

    Hello,

    There is something  in your circuit that is passing current through neutral that should not be present. 

    I was thinking the electronic load might be the issue.  If not there is something in your design causing this excessive current going through neutral. The load current of the 24V output should return to the 24 V output and not through neutral.  It sounds like your design is not truly isolated and there is a current path that there should not be.

    You might want to evaluate your PFC voltage and PFC current sense and PSFB CS and output when you do this test.  To make sure both of those circuits are functioning correctly.  The PFC could be causing the issue.

    Regards,