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Original question:

UCC28600: 2nd and 3rd Step is not understanding

UCC28600: Sec Ipk and Irms In multilple output(7) SMPS

Vivek Sen
Prodigy 90 points
Part Number: UCC28600

Tool/software:

Dear Mike O'

Your Suggestion given in " RE:  UCC28600: 2nd and 3rd Step is not understanding "

looking wrong as per my below details.

  1. When you change Vout and Pout for Vout2, Vout3 … Vout7 in the tool, it also changes Pin, I_PK,pri, and L_p. That behavior is fine for a single-output design, but it’s not the right way to extract per-rail currents in a multi-output flyback. In a real converter, the primary peak current and primary inductance are set once from the total output power (sum of all rails plus losses) at the worst case.
  2. Each secondary then “sees” that same primary peak current through its turns ratio. So per-rail calculations must not re-optimize the primary each time you edit one rail’s power.

Below is the relation B/W Ipk_pri and Ipk_sec.

Relation B/W Primary peak and secondary peak current        Relation B/W Sec rms and sec peak (Ip=Ipk)

  • 0
    TI__Guru* 86266 points

    Hello,

     

    TI at this time does not offer a tool for multi output flyback design.

    The instructions that were given to use the excel tool that were given will get you a working design.

    Each output should be capable of delivering the full output power if the other outputs are unloaded.  You should take that into consideration as well.

    The equations that you have given are correct for RMS current.  That does point out that one output could handle all the current.  So, you may consider using the tool set for the total maximum output power worst case for all outputs.  The other option is using step down converters on each output to limit the current of each.   This will improve load regulation.

     

    Regards,