Transformer for variable output off-line boost flyback converter
Transformer calculation is not an easy task.

As a start point you need to know if its saturating (more magnetic flux stored in it that it can get). That would, along other things, result in core losses. Its hard to calculate that, so its better to study this.

Also flyback drivers are commonly for &lt;100W application, what is the current you need, the cases of use of the SMPS, are great information.