Saturation of ferrite core in SMPS? 1

[schnell]

Hi,

I am designing an offline, isolated flyback at 22W with Vout = 36V, Vin=85-265VAC.

I will be using a EFD25/13/9 ferrite core transformer from Epcos(the AL = 315 one, N87)

Ferrit core datasheet:-

http://www.epcos.com/web/generator/...rchform&view=&distributorId=0&cssurl=&shop=no

On page 2 of the datasheet, it says Pv W/Set is 200mT....

http://i54.tinypic.com/34owms7.jpg

....but i thought the saturation flux density of most ferrites was 300mT?

My peak flux density is 220mT.

-do you think this will saturate this core?

 

[Skogsgurra]

No, that is not where the N87 ferrite saturates. It is the flux density where the loss Pv was measured. The V in Pv stands for Verlust, which is German for 'loss'.

EPCOS used to be Siemens components division, hence the French

You are safe with 220 mT. No problems.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[DHambley]

You do want to watch the power dissipation even though your flux is only 2.2kGauss. If your switching frequency were 100kHz for example, the core could see over 3W, which may crack that little core.

 

[schnell]

thankyou

hgldr:
did you calculate the 3We from the N87 material datasheet?

i thought EFD25 was about right for 22W SMPS at 100KHz?

also, i presume you are referring to core hysteresis loss's?

 

[DHambley]

Schnell,
Sorry, I was thinking of +/- 2.2kG and for a different core material. I think you're fine. Your 2.2KG peak flux roughly correlates to a +/-1.1kg flux swing with a sine wave. Since it's 1.8W max at 2kG (in the spec which I just looked at) your loss will be much less.

P = 1.8W times the ratio of: (1.1kG/2kG)^Kb Where Kb is usually 2.4 to 3.0 for most materials, so it looks like you're at no more than about 0.43W.

To answer your basic question, the core can handle about 3kg (or 300mt). the 200mT in the spec is a data point for the loss at 200mT. They don't mean that it's peak flux is 200mt.