Small 2W offline flyback power supplies....the flyback transformer core ferrites.

Hello,
We want to make ~2W offline flyback power supplies for bias supply.
Why is it that the Chinese ferrite transformer core datasheets don’t give the minimum core area? (Amin)...they only give the effective core area (Ae).
Also, why don’t the Chinese ferrite core datasheets allure to what frequency the core material is suited for?
Also, they give the AL value, but don’t tell what gap size gives this. We had one with an AL of 1100…this is quite high for a gapped transformer core…….and because they don’t state if its gapped or not we don’t know if its maybe some special ferrite with a low AL value?
We obviously need it to be gapped as it obviously gives the energy storage, but also gapped cores have tighter tolerance on AL value….so why don't the Chinese ferrite core datasheets give details on the gap size?
I know gap size can be calculated, but the fringing field gives an inaccuracy in the calculation.

Welcome to the world of Chinese ferrites....! see no evil, hear no evil, speak no evil ...

For a 2W power supply you can be somewhat liberal with tolerances. However, in case you are fussy, my personal suggestion is:

1. get a few sample ones and try them out.

2. if you are planning to get in bulk, ask them to supply from the same batch.

An air gap will increase the reluctance of the magnetic circuit but if the gap is less than (or about) 1mm, you need not bother about fringing.

The final characteristics of a given ferrite depends on the heat treatment and that can be something very tricky to master.

Thanks
Also Does anyone have data for type EE cores, or type EP cores for small flyback transformers. Neither ferroxcube or TDK list any data for these.
We also need the data on the former dimensions.

Treez

EE13 is the best choice for 2W flyback, use gaped core
http://en.tdk.eu/inf/80/db/fer/e_13_6_6_15.pdf
http://en.tdgcore.com/Private/Files/43309ee30d4e8d8e6cc5.pdf

Thanks, though i noticed that the first link doesnt give any details on pre-gapped cores.
The second link has good info on frequency characteristics for TP4 ferrite material, but doesnt show any details on pre-gapped cores available.

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We are also surprised that many of the ferrite catalogs don’t give the minimum cross sectional area of the particular ferrite core. (they only give the effective cross sectional area).....after all, if the flux density goes into saturation level in that part where the cross sectional area is smallest then we want to know about that.
Ferrite catalog which doesn’t give the minimum cross sectional area...........
https://product.tdk.com/info/en/catalog/datasheets/ferrite_mz_sw_e_en.pdf

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Hello
Please confirm that the bobbin depth of the EFD15/8/5 former on page 4 of the following is 1.67mm? This is gotten from [winding area / winding width]

EFD15/8/5
https://ferroxcube.home.pl/prod/assets/efd15.pdf

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Hello
We wish to wind a small offline flyback transformer for 1W. We wish to use an EFD15/8/5 former.
(we will use the AL=160 , EFD15/8/5 gapped core)

We have a primary which is 2 layers (54 turns) of ECW0.25 (max diameter = 0.297mm)
We have a secondary which is 1 layer of 17 turns of TEX-E (max diameter 0.417mm)
We have an auxiliary which is 1 layer of 32 turns of ECW0.2mm (max diameter = 0.239mm)

The bobbin depth is just 1.67mm.
The total thickness of the layers plus tapes is 1.52mm.
However, the total thickness of all layers , including all “return” wires, and tapes is 2.17mm.
(a ‘return’ wire is a wire coming back across the bobbin for termination).

The 3 layers of tape used will be 270um in total thickness.
I must admit this is an extremely tight wind.....we usually give ourselves a bigger former for this kind of thing, but in this case we are severely space constrained.

Do you think we will fit our turns on?

EFD15/8/5 core and former on page 4
https://ferroxcube.home.pl/prod/assets/efd15.pdf