Let’s say I am having ETD core and split bobbin for LLC Design I have 4 windings in that transformer

  1. primary
  2. secondary
  3. primary aux
  4. secondary aux

I am winding the primary and primary aux windings in one side and secondary and secondary aux in secondary side.

If I want to measure the leakage indcutance of the transformer,

  1. should I short all other windings without primary (or) only secondary winding (or) secondary side wounded windings only?
  2. if I wind the secondary aux in primary side then which windings should I short to measure the leakage inductance?
  • \$\begingroup\$ That depends how you want to model your transformer. If aux regulation is not a concern/fine anyway, I would just short the secondary. If you want a lumped total reflected on the primary side in your model, I would short all but the primary. \$\endgroup\$
    – winny
    Commented Sep 30, 2022 at 14:19

1 Answer 1


if I want to measure the leakage inductance of the transformer.

When you have more than 2 windings, leakage is no longer a single entity value; You'll have leakage from primary to main secondary and, leakage from primary to an auxiliary winding.

For a flyback transformer with an auxiliary winding, you would probably not be bothered about about leakage between primary and auxiliary because, the main problem will be "quenching" the unwanted part of the flyback voltage due to primary flux not 100% coupling to the secondary.

So, in my opinion, leave the auxiliary windings open circuit and short the main secondary to find the leakage. That is most likely to be the problematic area.

I expect it will be a similar story for an LLC converter design i.e. focus on why you want to know the leakage (because of possible problems it might cause) and figure out which windings to short and which windings to open circuit.

But, as with most of these questions, without a schematic, it's guesswork.

  • \$\begingroup\$ for LLC we are using integrated technique that is Leakage indctance is also considered for this LLC. i need to fix the values of leakage based on our requirement. i think no need of schematic for this LLC Transformer design \$\endgroup\$
    – Venkatesh
    Commented Oct 1, 2022 at 6:27

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