it is not new question, but supplement to my related question (unfortunatelly my previous qestion has been locked).
I have design small transformer for 2x5V output voltage.
I have used core with nominal AL=1200 [nH/Ts2] (core without air gap).
Primary winding consist of 2 turn (8 paralel wires - litz wire) and each secondary consist 5 turn (2 paralel wires - litz wire).
Primary inductance is 5,3uH and primary resistance is 53mOHM.
Secondary inducatnce is 28,9uH and 29,2uH and secondary resistance is 85mOHM and 85mOHM.
Converter with this transformer work wery well.