500W Full Bridge is giving too high delta B even with biggest core available

power electronics rule of thumb is 2 - 3 gap lengths away from the gap ( for the wire )

in the above - the Tx may not have been run for very long - or may have had unspecified airflow cooling - it does not pay to believe too deeply in any results published on the net that you have not re-created for your self ...

66kHz is not that high - the delta B is effectively +/- 150mT - depending on load and input voltage the Tx may not have been exercised to the full 0 - 300mT - 0 in the test ...

power electronics rule of thumb is 2 - 3 gap lengths away from the gap ( for the wire )

Click to expand...

..With that PQ2625 former, the centre leg is 12mm diameter and the former spool is 14.2mm diameter, so assuming it sits centrally in the core, then that gives a space of 1.1mm away from the gap. For a 0.42mm gap, then that means the windings are more than two gap lengths away, so it seems that that saved the day for the transformer.

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I remember being interviewed by a consultancy for a job with a world famous domestic goods manufacturer…they implied that a gap in a Flyback SMPS transformer should be no more than 10% bigger than the centre leg length…but didn’t say if this was due to fringing fields..Does anybody know?
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Also,
We are doing a 600W Boost PFC. Our PFC inductor is 600uH and we wish to wind it on an ETD49 core, with a 1mm centre leg gap. Turns are 44 TEX-ELZ as attached. In order to avoid overheating of the turns due to the fringing field of the gap, we will “pack up” the former with tape as in the attached.

Do you think this will result in a successful inductor, without overheating of the coil due to fringing fields? (Incidentally The i^2.R power dissipation, without considering skin effect, is 1.09W.)

Without the packing, the turns would be only 1.3mm away from the 1mm gap…violating the rule of “2 to 3 times”

it will definitely lower ac losses

power electronics rule of thumb is 2 - 3 gap lengths away from the gap ( for the wire )

Click to expand...

Thanks, the Boost PFC inductor of DER 547 has windings which are 1.2mm away from a 1.38mm gap.
This means they are too close to the gap. However, the windings are made of 40 strand Litz wire, and each strand is AWG38.
It does seem to be the case that if wires are made of ~40 strand Litz wire, then fringing field heating does not have an effect?
DER547

Once again, inferring tenets from the web is generally a bad idea ...

Thanks, in this case, i believe we would stick to the "packed up" coils of post #22 above....whether or not Litz is used, as this gets our coils far enough away from the gap.