# Some magnetic theory - theory of magnetic circuit

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#### Pina

##### Newbie level 4
magnetic theoy

Hello,
I've been through the books, but I just cannot find an answer. Let's say you have an E type core of known geometry and permeability. On it, you have a winding with N turns. My question is, how to you calculate the maximum current the core can handle without saturation, giving Bmax=0.3 T (for example...).

Any ideas?

Best regards!

magnetic theory

dB=(U*ti)/(w*Ae)

Re: Some magnetic theory

I've been through the books, but I just cannot find an answer.
In other words, you didn't understand the theory of magnetic circuit (relation of magnetization, permeability, flux) at all. I doubt, if it's helpful to answer with a formula in this case. Generally, you should look out for more basic literature or read the said books more thoroughly.

To give a short answer anyway, if you apply a magnetizing current to the core, it's primarly causing a field strength H, which has the unit A/m. Assuming an uniform ungapped core and no stray field, you simply get

H = N•I/le

le is the effective magnetic path length, it's given in the core data sheet. If you only know a Bsat value for the core, you have to find the corresponding Hsat from the magnetization curve, or calculate an estimated value from the known core µr.

P.S.: The Ferrite tool from Epcos.com can help you to do some core calculations.

Re: Some magnetic theory

Hi Pina !

Usefull theory about inductor and transformers design you will find in book on