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Original question:

UCC28910: New Transformer design & component values

UCC28910: Transformer for 13V output

Victor Chen_HK
Expert 5130 points
Part Number: UCC28910

Hello,

Is it possible to modify the UCC28910 EVM to output 13V using the attached transformer. The max output current is 0.3A and input range is 90V to 265V.

Thanks

Victor

  • 0
    TI__Expert 8210 points
    Victor

    You can use our excel calculator for UCC28910 (www.ti.com/.../sluc503) to verify what the optimal transformer parameters are. If you have a transformer that has different specification you can use this calculator to see what the impact on performance will be.

    When I go thru the tool it highlights that with the 3.5 mH magnetizing inductance that this transformer has the maximum switching frequency (which is at full load, minimum input) is 46.49 kHz. This is much lower than the 105 kHz max frequency that UCC28910 can operate at (which requires an inductance of 1.76 mH to achieve). This may cause the performance with this transformer to be limited. All the other parameters seem to be acceptable so it should work.

    Best Regards,
    Eric
  • 0 in reply to Eric Faraci
    TI__Expert 5130 points

    Hi Eric,

    Thanks for your reply. My customer also tried the calculation tool and replace the transformer on EVM with theirs. However, since the turn ratio has changed to Nps=160/30, Npa=160/39, the Vr reflected voltage and Vdd cap needs to be changed as well. They changed the Vdd cap to 44uF but burned the fuse when power up. Do you think there is any other components need to be changed? I'll get their transformer and try in TI lab next week so I want to make sure it works.

    Thanks and best regards,

    Victor

  • 0 in reply to Victor Chen_HK
    TI__Expert 8210 points
    Victor

    I am assuming the design is based off of UCC28910FBEVM-526. The total VDD capacitance on this EVM is 10.1uF. Increasing it by 4x will extend the startup time drastically. I recommend verifying the following parts of their design with the excel calculator linked earlier.

    - Did they recalculate the voltage stress on the primary and secondary windings to make sure the voltage ratings of the semiconductors and capacitors are correct?
    - Did they adjust the preload resistor to accommodate the different output voltage?

    Best Regards,
    Eric
  • 0 in reply to Eric Faraci
    TI__Expert 5130 points
    Eric,

    No. They did't change any components other than Vdd cap.

    The output bulk cap is the only component with wrong voltage rating as I was doing calculation. I'll change it before doing the test.

    For the preload resistor, I think higher ouput voltage means it can use higher value preload resistor. So keeping the preload resistor(smaller resistance) on EVM unchanged should be fine.

    Best regards,
    Victor