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Core size for off-line converters

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kekon

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How to calculate correct size of the core for off-line converter ? (core volume in mm3)
I read about some principles of how to do it basing on graphic methods but the information given is very general. I have all the neccessary parameters: core material, frequency, output power, primary inductance, air gap etc.
 

E-design

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Hi

There are a lot of trade-offs, like switching losses, temp rise, core losses, radiation, topology, form-factors etc. There are programs out there that will evaluate all your inputs and determine if the core size is suitable for the application.

Working from graphic plots make it easy to instantly do "what-if" scenarios. Reading a good book like the Keith Billings book available for download somewhere in this forum will help you a lot if you are a novice in designing transformers.

Like with everything there is no substitute for experience in becoming good at designing switching transformers.

Sloppy construction may doom a perfect theoretical design if you are not careful and you ignore things like leakage inductance, packing of windings, flux-balance etc.

E
 

Mr.Cool

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yes, get the book "switchmode power supplies handbook" available in the Ebooks upload/download section. well, actually the book should be removed from there (it is too large to fit in elektroda) but info on where to find it elsewhere is posted.

i would strongly suggest not to use excell spreadsheets or other computer programs to design transformer. they are hard to work with, you basically have to know ALL parameters before you try to use them (which would make using them pointless...).

i do not have much experience with designing transformers. i have done only one for a flyback converter. in that topology the core size was only considered once i knew other paramaters such as Gauss swings. then i choose minimum core size such that there is enough window size to wind all windings & layers, and dimensions to not exceed design constraints. basically, core size was a by-product of transformer calculations - not a critical issue.

but read the recommended book, it is good on this topic.

Mr.Cool
 

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