Tny264 current limiting problem

I am new to electronic. I want to build 12v smps cv/cc. I find ic tny264. But I don't know how it limit the current. Datasheet say it suitable for 5.5w. But current limit of mosfet is set to 250mA. According to that 65% duty cycle them we get around 149.5 volt on primary side. Then 149.5 x 250mA = 37 watt.
Can anyone can explain why is this.? Or I have to use current limiting on secondary side.

You need to learn basic electronics for the next 5 years and then come back with this question.

The device is used as a switch so it is either full on or full off.
In that case the power dissipation in the switch is not the voltage times the current. That power is dissipated in the load.