Hi,
Sometimes transistors explode in converters because something goes
wrong and the transistor draws a huge current. Because of this a fuse
is needed to cap the max energy available to the transistors in case
of a failure. It also prevents circuit traces from blowing off the board
because of excess current too.
You need to study transformer design a bit as you need some leakage
inductance to help with the flux 'ratcheting' effect.
If you cant find anything else, try OnSemiconductor's site. They have
excellent power converter app notes and other documentation.