Consideration factors before going to custom magnetic request from manufacturer, an app note from Vishay. Link here (PDF)
There are many manufacturers that claim they build custom magnetics. However, there is often confusion as to what constitutes custom magnetics and whether or not a designer actually needs them or can afford them. This article will clarify what custom magnetics are, help designers determine if they are needed, and explain how to engage with a custom magnetics supplier.
from Dangerous Prototypes http://bit.ly/2FM8eZ9