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Permissible frequency range of Epcos ferrite material in SMPS transformer?

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treez

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Hello,
We wish to use a PM core by Epcos for a switch mode transformer. These only come with ferrite materials N27 and N87.
We are doing a full bridge converter, 2kw, vin=380vdc, vout = 360vdc.
The Epcos ferrite databook does not specify what is the permissible frequency range of these materials.
Do you know what it is?

Epcos ferrite databook
https://en.tdk.eu/blob/519704/download/2/ferrites-and-accessories-data-book-130501.pdf
 

brushhead

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What you are looking for is the loss per cubic metre, and the ∆ flux density at which you operate. The change in flux density is directly reflected in the losses in the core.

Rob.
 
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brushhead

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You should not be operating anywhere near the Bsat value as your losses will take the core through Curie and your transformer will no longer work, and you may also shatter the core. Normally you don't operate above 200mT in my experience. Clearly that is also based on the characteristic of your core material.

Rob.
 
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mtwieg

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It's in the databook, check pages 34, 41, and 83. Both have ratings given up to at least 100kHz, N87 goes up to 500kHz.
 
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Warpspeed

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If you were running down at 20Khz, it probably does not matter, as you will be saturation limited, not core loss limited.

The N27 material is now pretty old, and it still works fine for many lower frequency applications, but the newer N87 has lower losses at higher frequencies. The higher you go, the better N87 becomes.

As you go higher in frequency the losses increase, and you will need to reduce the flux swing to limit temperature rise.
There is really no fixed upper frequency limit as such.
You just need to drive it less hard as you go higher, and larger sized cores with greater internal volume will reach higher internal temperatures, everything else being equal.

A lot also depends on the expected ambient temperatures reached inside the equipment, its all more a judgement call than anything else. In the end it probably comes down to running some practical tests.
 
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