Mixed core for LLC......Ferroxcube and TDK

[cupoftea]

Hi,
Doing 2kW LLC, Vin=390v, Fsw~50kHz.

For the resonant inductor, will use a 3C94 ETD59 ungapped core from ferroxcube, with a 2mm gapped core (N87) from TDK......will this be OK?.....will wind turns and check the inductance factor.
They appear identical WRT core loss and permeability, so it should be just like its an ungapped N87 core half from TDK?

3C94

https://elnamagnetics.com/wp-content/uploads/library/Ferroxcube-Materials/3C94_Material_Specification.pdf

N87

https://www.tdk-electronics.tdk.com/download/528882/71e02c7b9384de1331b3f625ce4b2123/pdf-n87.pdf

 

[cupoftea]

The N87 core half has the 2mm gap and an AL value of 311 when mated with an ungapped N87.

https://www.tdk-electronics.tdk.com/inf/80/db/fer/etd_59_31_22.pdf

The 3C94 half is ungpapped and has an AL value of 6000, when mated with an ungapped 3C94

http://ferroxcube.home.pl/prod/assets/etd59.pdf

...so to find the overall AL value..is it a case of working out the reluctances of each core half and then doing the F=Phi.Reluctance equation?

 

[cupoftea]

..i actually dont think its possible to calculate this very accurately, due to the unknown exact extent of the fringing field in the gap and around it.?
Its probably better to say that AL=311 if all ferrite is N87...if the ungapped half is 3C94, then 3C94 's AL value is 13% greater than that of N87, so therefore, halve that (as only one half is 3c94), giving 6.5%....and then say AL with the 2mm gap is 311+ 0.065*311 =~ 331. Would you agree? We will measure it aswell....with home made resonance inductor meter. (but this uses 5% cap, and we cant yet afford accurate capacitance meter)

 

[FvM]

Your calculation approach is basically incorrect. Total AL value is dominated by air gap reluctance. If ungapped AL varies by average 6.5 %, gapped AL variation will be less than 0.5%.