# B max flux density

#### MATT838383

Joined Jul 31, 2019
144
Hello everybody i have a question on Bmax calculation for the numbers of windings of a ferrite transformer
N(prim) = Vin(nom) x 10°8 / 4 x f x Bmax x Ac
(i dont have the numbers of turns!) thanks a lot

#### ci139

Joined Jul 11, 2016
1,898

#### MATT838383

Joined Jul 31, 2019
144
Sorry a need only the value of Bmax in tesla or gauss for a etd34 thanks!

#### MATT838383

Joined Jul 31, 2019
144
hello can anybody help me?

#### Alec_t

Joined Sep 17, 2013
14,395
Check the datasheet for the particular ferrite core that you have.

#### TeeKay6

Joined Apr 20, 2019
573
Hello everybody i have a question on Bmax calculation for the numbers of windings of a ferrite transformer
N(prim) = Vin(nom) x 10°8 / 4 x f x Bmax x Ac
(i dont have the numbers of turns!) thanks a lot
Bmax is limited by whichever ferrite material you use. As @Alec_t says, look at the datasheet for your core.

#### MATT838383

Joined Jul 31, 2019
144
Ok thank you i check it on datasheets!

#### MATT838383

Joined Jul 31, 2019
144
Just checked the data sheet of my ETD34
i have found no tesla or gauss value!
can everybody help me for tesla or gauss calculation?
thank you

#### MATT838383

Joined Jul 31, 2019
144
here is the file

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#### Jony130

Joined Feb 17, 2009
5,539
Typical we assumed the B_amx around 250mT or less.
But what you want to calculate?

#### MATT838383

Joined Jul 31, 2019
144
Hello Jony130 thank you for your answer! i want to calculate the numbers of windings of the ferrite transformer for a power swiching supply!

#### MATT838383

Joined Jul 31, 2019
144
So the estimation of Bmax to 250mTesla can work with this formula:
=(12x10°8)/(4 x f x Bmax(250) x ac)
thank you

#### MATT838383

Joined Jul 31, 2019
144
Some one could tel me if the formula can work?
thnks

#### DickCappels

Joined Aug 21, 2008
10,245
By the way, in the datasheet the abbreviation mT is used for flux density (milli Tesla).

#### MATT838383

Joined Jul 31, 2019
144
Ok Jony130 i wil find the gauss that i need ! thank you!
Thank you Dcappels i will check that!

#### MATT838383

Joined Jul 31, 2019
144
So the value of the core is 97mm²
the formula is for etd34
(12X100000000)/(4X(100000KHZ)X(330BmT)X0,97)=9,37 turns! is that too much?
thank everybody!

#### Jony130

Joined Feb 17, 2009
5,539
And for this equation yot have given you need to plag the flux density in Gauss not in Tesla.
Effective cross-sectional Area in cm2 and the frequency in Hertz

Last edited:

#### MATT838383

Joined Jul 31, 2019
144
Ae effective area =97mm²
so if i convert tesla in minitesla and frequency khz in hz i do:

(12X100000000)/(4X100000hzX330BmTX0,97mm²)= 9,37! is that rigth?