#### sabu31

##### Full Member level 4

I am having a confusion regarding the method used for selection of core size for high frequency converters. I know there is Area Product Method and Core Geometry Method.

I studied core Geometry method presented in both mentioned in Transformer and Inductor Design Handbook by Col. McLyman and Another Presented in Fundamentals of Power Electronics by Erickon and Maksimovic.

In First method its using formula for Kg(electrical)= Energy^/(Ke*Alpha)

where

Ke=0.145*(output power )*(Bm)^2*10^-4

Alpha is regulation in %

In second method

Kg=(Rho*Lm^2*Im,max^2*Irms_tot^2*10^8)/(Bm^2*Pcu*Ku)

where

Pcu is copper loss

Bm is max flux density

Ku is winding utilization factor

Irms

Im is peak magnetising current

Lm is primary inductance

But both these valuations are giving different values of core geometry. Based on Geometrical size we are getting

Kg=(Core Cross Section)^2*(Winding Area)/(MLT) (Based on Erickson Formula)

Kg=(Core Cross Section)^2*(Winding Area)*Ku/(MLT)

However, despite the only difference in them being Ku. The calculated values of Kg requirement (based on electrical condition) is different from Kg (based on core specifications). From my calculation Erickson Kg method is giving values close to whats required and can be applied using manufacturer core specification datasheet. From Col. McLyman method I have to depend upon tables givnen in the book.

a ) Is there any thing missing in my understanding, why this difference is arising and whats correlation between them.

b) Secondly, in TI app note they are using Area Product Method .Using a definition given as

AP= (LmIscspk*Ifl/(Bm*Ku*J*10^-4))^4/3

There is another formula

Ap=2*Energy10^4/(Bm*J*Ku)

Which is more accurate or commonly used.

c) Which is the method commonly used by magnetics designers (Area Product or Core Geometry. And whats relating all different formulae