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UCC28C56H-Q1: Output regulation issues

Part Number: UCC28C56H-Q1

Hello TI.

When unloaded, we have around 95V and when fully loaded we have 62V. Is it possible to improve this somehow? Maybe Rfbu is too high? How can this be troubleshooted?

Attached transformer datasheet, do you think it could have an impact as well?

750371610r00 Spec.pdf

All inductors, common mode chokes and ferrite beads are NM (set as 0ohm resistors).

Any help is highly appreciated!


  • I was about to make a new thread but i figured that its a related topic so i will post it here:

    We want to increase Vout because the transformer goes up to 90c at room temp. Reducing Iout and increasing Vout seems to help but due to unloaded voltage being so high we risk of developing other issues. 

    So an extra question - are there any good ways in reducing the transformer temperature? 

    We have asked Wurth if they could increase the coil diameter, but not sure if its possible within the same package.


  • Valentinas,

    The first thing I would check is to verify the regulation of the primary AUX winding is what you expect. Next, how does this relate to the cross-regulation of the VOUT voltage? Reducing the FB resistor values will present a higher AUX load during light load operation and this may help. You are seeing a variation of ~53% but for the TI EVM, we are seeing VOUT load regulation variation as (22%-4%=18%):

    Reducing the transformer temperature would require knowing more details about the source of the power loss. Ideally, the transformer is constructed to balance copper and core loss but in reality, decreasing the physical size or increasing the isolation spacing can force the need to move away from "ideal." If you are constrained to the physical size you are currently using then there is little you can do to reduce core loss by increasing cross section. If the windings are getting hot I would first try to minimize the number of layers but this might require a wider window area (different core size/shape). You should work with the designer at Wurth to underrated the details of the transformer they are constructing for you.

    Steve M