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UCC2897A: Use the Current Transformer in UCC2897A with high-side or low-side

Micky Shih
Prodigy 230 points
Part Number: UCC2897A

Hi all,

I use the Current Transformer (CT) in UCC2897A , then I put it in the high-side (picture 1).Can I put the CT in the low-side(picture 2)?

I think the current is same in the hide-side and low-side. What is different between the two?

I think put in the low-side, when ground signal interference, the CT will be disturbed. But the general design will put current sense resistor in low-side.

What are the advantages and disadvantages of the two.

It doesn’t have to be applied to UCC2897A, I want to see the design applied in other places.

Thanks!

Micky

  • 0
    TI__Mastermind 32975 points

    Micky,

    SLUA535 section 4.6 details the proper use of the CS Xfmr in the active-clamp topology. TI recommends the high side VIN a, above the transformer primary, as the lowest noise, best location for sensing current. You can certainly apply the CS Xfmr in either of the two places you marked on your schematic. We use CS resistors in the low-side of the primary MOSFET when the primary current through a resistor is thermally acceptable. The nice thing about the CS transformer is that the primary is essentially floating and can be applied anywhere in the circuit and the secondary is GND referenced no matter where the CS Xfmr is placed. In a proper PCB design, all the high current GND return connections should converge at the source of the primary MOSFET so while it the most convenient place to sense the current, it is not the best location and this is especially true when the current is so high, we need to use a CS Xfmr. Thanks for connecting through E2E.

    Regrads,

    Steve

  • 0 in reply to Steven Mappus1
    Prodigy 230 points

    Hi Steve,

    In addition to placing the CT in Vin input test, most of the other types of products will be placed in hide-side or low-side?

    Because I have seen both positions and want to understand the difference, is there any discussion in this part?
    Or the two are actually the same, because the other end is grounded.

    Thanks!

    Micky

  • 0 in reply to Micky Shih
    TI__Mastermind 32975 points

    Micky

    Please check out Active Clamp Transformer Reset: High Side or Low Side? describing the differences and trade-offs between high-side vs low-side active clamp. If you don't read the entire app note, at least pay attention to the summary in Table 1.

    Steve