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16W offline flyback with EFD15/8/5

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Advanced Member level 5
Jun 13, 2021
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The attached is a 16W, 24V isolated Flyback. 100-265VAC
Uses TOP264.
Bpk is 292mT
Core loss is 0.163W
Fsw = 132kHz
There are no electrical overstresses.
Why will the chip maker refuse to support it? Refuses to supply us with samples, and says we must just give them the spec and let them do it all for us. They say its a poor design,
We are constrained in having to use the EFD15/8/5 core set due to lack of room.

The peak primary current is 1.2A. Peak secondary current is 4.97A.

I checked the core loss's for 3F3 and they are not bad. It uses the AL=63 core set.
The turns ratio is 58/14 = Np/Ns.
It is as attached. Surely there is nothing electrically or magnetically stressful about this?
There is blown air blowing all over this flyback ,and the enclosure has vent holes to the outside air.


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for 16W the TOP264 is likely a little bit undersized - cooler is always better

surely it's easy enough to buy samples ?
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Thanks, we have to use TOP264 because if we pick eg TOP265 then the peak current in it is too high.
We have blown air.
Yes we can buy samples, sorry i meant.....the boss wont support the design unless PI Expert or PIXLS will ratify it....but those software wont do this design...i dont know why.......

Worst case rdson (at 100c) is 9.2 ohms...that would give 2W conduction loss in the TOP265 when at 100vac.....i think with the blown air that would be fine.......i mean, maybe we can stick a little "SOIC8 style" heatsink on it too.

Thanks, sorry i didnt explain well enough.....i meant the fixed peak current level in TOP265 is way above 400mT for us. Power integrations themselves recomend at startup/sudden overload etc etc , Bmax should be no more than you know, there are those occasions when the peak current will go above what it is during steady state operation at nominal load.
--- Updated ---

page 20 they speak of the peak current rating of the PI controllers

"A value of 3800 gauss
at the peak current limit of the selected device together with the
built-in protection features of InnoSwitch3-EP IC provide sufficient
margin to prevent core saturation under start-up or output s/cct conditions."
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These things have a soft start ( 17mS ) and regulation - so you don't see the rated peak current - unless the output is severely overloaded ..... i.e. no current limit.
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