Hi,
Is 6A/mm^2 ok for smps transformer windings.....84KHz switching frequency.....natural convection cooling
Is 6A/mm^2 ok for smps transformer windings.....84KHz switching frequency.....natural convection cooling
No, my old rule of thumb is 400 A/cm^2. This is for a few (or 1) layer(s) where the heat can easily be removed from the windings. If you have multiple layers, then you need to reduce the current density.
A transformer manufacturer just recomended 12A/mm^2 for an etd44 ferrite core in a 90-265vac full bridge at 84khz.
he told me not to worry about skin effect cuzz the freq was too low
he told me not to worry about skin effect cuzz the freq was too low
You'll find this document useful: www.coremaster.com/appnotes/an107.pdf
Even though it's for a supply with a different topology and purpose, the transformer calculations stay the same. You will see that knowing the dimensions of the transformer they simply use the mean length of a turn to calculate dissipations in the wire. I use a similar method. Now a bunch of people will chime in and say there's proximity effect, skin effect, core losses, and so on. Well, core loss is another parameter that you can get from the manufacturer, and either way, calculating the copper loss and taking that into account in your design is still better than just using a constant.
Even though it's for a supply with a different topology and purpose, the transformer calculations stay the same. You will see that knowing the dimensions of the transformer they simply use the mean length of a turn to calculate dissipations in the wire. I use a similar method. Now a bunch of people will chime in and say there's proximity effect, skin effect, core losses, and so on. Well, core loss is another parameter that you can get from the manufacturer, and either way, calculating the copper loss and taking that into account in your design is still better than just using a constant.
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