Hello,you say you switched off then back on again......so when you switched back on, the NTC would have been warm, and there would have been potentially very high inrush into the 270uF primary capacitor...which could have blown the 1A fuse.....especially if you inadvertently switched back on at the peak of the mains.
But you say the fet pins are shorted...all 3.....uummmm.
Was your sec feedback working?.......the LT1241 has no overload protection....no timeout function
Thanks, I will check the source resistors. I am not sure how hot the NTSC was since it took 1 hour until I switched back again (when the fused get blown) and I recalled that the power supply was not too hot at that timethe 68uH choke in conjunction with the 1uF cap following could easily over volt the fet at turn on if the ntc is hot.
--- Updated ---
also -- check the source resistors
Thnaks, so I need to perform these steps:Anyway, so its difficult to say exactly what caused the short to the fet, but attached is a re-run of your shown schematic, with what, IMHO, are some improvements. Only the salient bits are shown.
I assumed the transformer as shown, and a power of 62W. Please tell if much different.
The grounding situation with the sec side opamps didnt look so good, so i re-did it as attached....the attached is in the free LTspice simulator, and shows it at 13.5v 4.5A charging.
As discussed, the LT1241 needs swapping out really too.
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