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UCC28711: Guidance on designing 3-phase AC/DC converter (350–500 V RMS) → 24 V / 3 A auxiliary supply similar to TIDA-00173

Anand Kumar
Prodigy 40 points

Part Number: UCC28711
Other Parts Discussed in Thread: TIDA-00173,

Hi Team, 

I’m designing a 3-phase AC/DC auxiliary power supply with an input range of 350 V to 500 V RMS (50/60 Hz) and an output of 24 V DC, 3 A, targeting efficiency above 85% and low EMI.

I referred to the TIDA-00173 reference design but found a few unclear parameters specifically, the Dmag definition, the change in transformer turns ratio (12:1 initially and 18:1 later), and how the VAON voltage of 5 V is derived. Could you please clarify these points or suggest any TI reference designs or documentation that cover similar specifications, including guidance on flyback transformer design for wide-range 3-phase inputs?

Thanks in advance for your help. 

  • 0
    TI__Expert 3665 points

    Hi Anand,

    Thanks for considering using TI products. 

    Please see my comment embedded in red.

    1) Dmag definition: 42.5% is max Dmag for UCC28711. For more detail, please refer section "9.2.2.4 Transformer Turns Ratio, Inductance, Primary-Peak Current" in its datasheet.

    2) The change in transformer turns ratio (12:1 initially and 18:1 later):  Its approx. 12 only not 18, kindly check below png for comparison. Here, Np/Ns = N1/(N2+N3) = 35.5/(1+2) = 11.833 = approx. 12 (as mentioned in calculation in design guide)

     

    3) how the VAON voltage of 5 V is derived? >> VAON = Rds(on)*Ipri(rms) = 5ohm * 1A = 5V (this is most probably rough estimation), however actual VAON = Rds(on)*Ipri(rms) = 4.2 ohm * 0.334A = 1.4028V. Also, it mentioned in design guide that 5V VAON is estimated value (FET USED here is STF2N95K5).

    I hope this helps to resolve your query, and you can continue to refer TIDA-00173 as reference design.

    Thanks

    Regards

    Anita