I noticed that I was mentioning Rdc throughout. I mixed up Kg design methods for the inductor and the flyback transformer designs.
- - - Updated - - -
See this document for a simple lab to gain a good insight for the Kg method.
https://www.google.com/url?sa=t&sou...FjAAegQIBRAB&usg=AOvVaw3eJu5Fa3qcdrHnDgvavxSH
- - - Updated - - -
There are a few differences other than Ku. From the two Kg methods, notice that the McLyman method uses (Ipk^2)^2 and the Erickson method uses Ipk^2*Itot^2.
Just write them out and you'd spot the difference.
Thanks Akanimo for the reply. I will explain my self clear with an example from infineon design
I will make my self clear through an example
Using Infineon Application Design for a DCM Flyback. I am using the calculated values in the design note
Vout 12V, fsw=65kHz, Po=25W. The values calculated are L=407uH, Ip_pk=1.53A, Ip_rms=0.58A, Is_rms=3.9 A ,Bm=0.3T Ku=0.3(Assumption), Alpha=2% (Pcu/Po*100) (Assumption)
Using Handbook method I am getting the following
E=0.5*L*Ip_pk^2, we obtain E=0.00047 Ws
Ke=0.145*Po*Bm^2*10^-4, we obtain Ke=0.000016 (I am not clear what 0.145 factor is about)
Kg(calculated)=E^2/Ke*Alpha= 0.0067 cm5
In Design note they have used E20/10/6(EF20)
Ae(cm2) Aw(cm2) MLT (cm) Ap (cm4) Kg(cm5)
EE20 0.321 0.34 4.12 0.10914 0.002551
The core geometry for this from the core and bobbin specification is 0.00255 cm5
[using formula based on core specification mentioned in handbook Kg= (Winding Area * Cross-Section ^2*Ku)/MLT]
As per handbook this core is not suitable
Now in in Method Mentioned in Erickson
Using Pcu=0.5W (0.5/25*100) (So that Alpha=2, and loss component is similar in both methods)
Rho=1.724*10^-6Ohm-cm
The Required Core Geometry based on power requirement using formula Kg=Rho*L^2*Ip_pk^2*Ip_rms^2*10^8/(Pcu*Ku*Bm^2)
The value obtained is 0.00749cm5
The calculated Core Geometry based on specifications Is = Winding Area * Cross-Section ^2)/MLT]
Kg=0.0085cm5 which shows the core is able to meet the requirements.
Now both the books are very well accepted. So what is wrong in my understanding of the method for calculation for core geometry using Handbook method. I like handbook method since it uses skin effect and fringing effect etc. However, I am not able to apply to data sheets of manufacturers. So what should be corrected in my assumptions/calculations.
- - - Updated - - -
Thanks Easy Peasy for the reply. However, I wanted to know regarding core geometry calculations difference in method by Mc Lyman and Erickson. Which method do you use.