Hello friends,
.
I want to design flyback converter but I have problems.I added image about it.Can you look it?
Vin:15v
Load:800 ohm
Vout:30V
Duty cycle:0.6
switching frequency:100kHZ
Hf transformer Ns/Np:15.8
Hf transformer power capacity:500W
Normaly, flyback converter formula is: Vout: Vin*n*(D/1-D):15*15.8*(0.6/0.4):355.5V

What is the my mistakes?

 

What is the DC resistance of the primary and secondary windings?
What is the inductance of the primary winding?
Is the diode and capacitor rated at 400V+?
Is the diode a fast recovery type?
Does whatever you are using as the switch fully saturate in the 'on' state?

 

Your switch (likely a transistor of some sort) needs to withstand at least 30V plus the peak caused by the leakage inductance. Consider a snubbed to protect the switch.

Show a photo of the waveform on the primary.