@ Yoosef
10 Years ago with my first attempt to build a SMPS, I built that circuit, and it worked fine, it was my first regulated SMPS.
But I never completed a regulated SMPS, at least in the last year.
But now I am moving to the new LLC SMPS topology.
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@ Silvio
I had my ETD39 working fine with 20 Turns at primary. what core temperature you have in idle with your ETD39? at 28 Turns in primary?
Maybe there is a reason?