How to calculate inductance of powdered iron inductor in DER484

The "Fit equation" in the Mag-Inc powder core catalog gives the inductance as 283uH.
This is with the 75 Turns and 4.6A of DC Bias.
As you know, the equation allows you to calculate the reduced value of ur, from which you can calculate reluctance, then use this to calculate inductance = N^2/Reluctance. It gives 283uH.

Dear Treez.


Thank you very much for reaching out to us.
Regarding your question, by inserting the desing parameters into the Fit equation provided by Mag-Inc you get a value of L equal to 244 uH. ( this is considering a input drive H of 60 AT/cm and L0 = 883.125 uH)


HiperTFS2 PIXls spreadsheet, as you pointed out, calculates a value of inductance at full load of 229.4uH, the difference betweent the two values is about 5%, it can be explained by the fact the the spreadsheet utilizes a slighlty different apporach to estimate the value of reduced permeability vs DC bias.


Hope this helps.


Best regards
PI-Start Lord

Hi,
With 75 turns, path length of 63.5mm and 4.6A of current, the AT/cm is 54.3 AT/cm.
I am not sure where the 60 AT/cm comes from?
The 229uH, which is calculated in DER484, is the inductance at the peak of the output inductor current, considering that the inductance is constant at 283uH from peak to pedestal of output inductor current. The 283uH is the inductance found at 4.6A of output inductor current (which is the average).
Also, DER484 calculates core loss as 0.62W, whereas the workings attached show it is 4.5mW. It is very low because the ripple current is low and B=uo.ur.H and as current rises, so H rises, but B doesnt rise significantly because ur gets less as H rises.
My workings are as attached.
Please show workings for DER484 output inductor value and core loss?

Dear treez.

Thank you for you comments.
60 AT/cm is the magnetic field strenght at the peak of the output inductor current, therefore, as you already pointed out, 229 uH is the output inductance value at the peak current.
When it comes to the loss value, while reviewing the output choke core loss calculation we found a small typo in the conversion from Gauss to Tesla. After the correction the core loss value is 6.5mW. The 2 mW difference to your calculation might come from the fact that the spreadsheet uses some default and fixed values for the core constants a,b and c which appear in the core loss equation. We might review them and update accordingly.
The spreadsheet will be promptly fixed and updated in PIExpert.
Thank you for you contribution.

Hope this helps clarifying your doubts.

Best regard
PI-Star Lord

Thankyou so much.