I was reading a book, "switching power supply design - Abraham Pressman", specifically the section about flyback converters. One part I'm not quite sure I understand is where he says that the saturation of the primary coil could destroy the driving transistor.
I went back to school on how inductors work and I think what will happen is this. At time zero when the transistor turns on, current will begin to flow slowly and the magnetic field will build up in the inductor. Current flow will increase as time goes on and this will increase the size of the magnetic field. At some point the core material will become saturated, meaning that even though you pump more current into it the magnetic field does not increase very much.
It was this build up of the magnetic field that was protecting the FET in the first place, but now that it's saturated its inductance will begin to drop. So effectively the impedance of the coil is dropping and more and more current now wants to flow through the transistor. Eventually that current times the RDS on of the FET will exceed the power rating of the package and the FET will melt down.
Am I understanding this correctly?