I have a flyback transformer which I took off the shelf.

It has 6 outputs:

  • 4 at secondary side and
  • 2 (+1 input) at primary side.

I'm able to approximately know consumption of each output.

How much can I draw from each output?

I think that each maximal output current is function of the other maximal output current.

Does it depend on how each output contributes to saturate the core?

If you have any documentation about this subject, I would be really thankful.

  • 3
    \$\begingroup\$ It's not the output current that saturates the core but the input current into the primary. Do you have a data sheet for the part? \$\endgroup\$
    – Andy aka
    Commented Mar 18, 2020 at 9:36
  • \$\begingroup\$ I have a paper datasheet ! What do you want to know ? I will appreciate if you give me the method rather than computation. \$\endgroup\$
    – Jess
    Commented Mar 18, 2020 at 9:39
  • \$\begingroup\$ Core cross section area, Al value and number of turns on the primary. \$\endgroup\$
    – winny
    Commented Mar 18, 2020 at 9:43
  • \$\begingroup\$ @jess as winny says, core dimensions, plus... ferrite core material, number of turns, gapping used, proposed operating frequency, proposed primary voltage, leakage inductances.... \$\endgroup\$
    – Andy aka
    Commented Mar 18, 2020 at 9:46
  • 1
    \$\begingroup\$ Precisely what do you need to know and, if you say you want the whole theory behind how a flyback converter works then, it takes a book to fill and might possibly be summarized in 5 sides of paper. Focus on what you want then tell us what you want. Nobody is going to provide a generalized answer that might hit every base for all men. \$\endgroup\$
    – Andy aka
    Commented Mar 18, 2020 at 10:40

1 Answer 1


Main limitation factor is temperature. Each coil is heated by its own current and they all heat the transformer as whole. Also, some heat dissipates in the core itself. So, you can trade the current of one output coil to another. But usually each coil is made by the wire of specific cross section, fitted to nominal current of that coil.
Total power rating of the transformer is a function of geometry size and working frequency, so it may be guessed. Then, that power divided by voltage of any output coil will give an estimation of the maximum current for that coil in case other coils run idle. Usually in such condition, that coil will suffer moderate overheating.


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