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Full Bridge LLC of 4kW not possible with offtheshelf gapped cores

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Do you agree that a 4kW Full Bridge LLC converter, with vout = +/-180Vdc and Vin = 390Vdc (PFC output) cannot be done with any offtheshelf gapped ferrite core sizes? (That is, cores that can be bought ready_gapped)

AYK, the biggest gapped ferrite core available offtheshelf is the ETD59 which is offtheshelf gapped to 2mm (AL = 311). However, if that is used as resonant inductor or (external) magnetising inductor of such an LLC, then its core losses will be too high (approx. 10W).

Would you agree with this? Or can you design one which doesn’t suffer such high core losses when only offtheshelf gapped cores are used.

The attached shows the design document for such an LLC. Done at 70kHz….the core losses come out at 10W for the resonant inductor, and 10W for the magnetising inductor, which in both cases uses the ETD59 TDK core with N87 , ready gapped with 2mm gap. These core losses are too much, would you agree?

No, Farrington.

To summarize your misconceptions

 a 4 kW inverters loss budget easily accommodats 20 W Pfe.  Pcu may be similar.

Gap calcution depends on the overall topology, frequency, inductance and Bmax

Stock gapped cores are in several gap sizes,

expect 1..3 yrs delivery and MQ 10K sets

We use un gap cores and place a fish papers or G10 gap.

Our inverters had no gap in the transformers.

bon courage


Thanks jonpaul,

I like the idea of sheet gapping, but fear  of its inaccuracy, and wide tolerance.

Also, thats now two of us that spell my name wrong!....its supposed to be "Farringdon", after my favourite area of London.
..will see if i can get it changed.

Also, i still declare that a 4kW LLC converter cannot be done  off PFC output (~390V)  with offtheshelf gapped ferrite cores.....so the ETD59 is the biggest offtheshelf gapped ferrite core with 2mm gap to AL=201.
It is simply not possible...would be too much core loss even with fan cooling on  the ferrite and vented enclosure in max 35degc  external ambient.
Would you agree?

No, I disagree, and I have personally made an LLC converter processing more than 10 kW with an off-the-shelf gapped PQ65 core set.

Thanks, but PQ65_with_gap  is not "offtheshelf"......at least not with major vendors........and not universally gapped amongst the different vendors.
Whereas ETD59 is standard gapped to up to 2mm.
You must have had that gapped?...or sheet gapped it?


[EDIT.]...My apologies...it is actually available"distributed gapped" off the shelf..(if you can find it in stock like that)......but £46.44 a piece on digikey...12 in stock

....that to me is just as pricey as getting it gapped yourself....so it woudlnt count for us....though my apologies , because i forgot to add that  "if available off the shelf, then mustnt be of a price equivalent to getting it gapped yourself"

Price falls with volume of course..but so do the others.
For comparison, if you will, please see offthe shelf gapped ETD59......£3  a piece......


As such, ETD59 is  the biggest of the  'realistically offtheshelf gapped ferrite' available....but it woudlnt be possible to do a 4kW LLC off 390Vdc with a ETD59....thats the postulation....unless others may differ?


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