thermal problem in smps [with sg3525] 12V/315V DC to DC converter

I've made a DC/DC converter [12V to 400V] with SG3525, PCB diagram is given below:


the converter works fine upto 100W, but when I connect a 200W load smokes comes on from shunt resistors. But if I don't use the shunt resistors, MOSFETs blows away. the switching wave-shape is:


MOSFETs used: 75n75*2 in each channel, Diodes are UF5408, 1n4937, 1N4148,1N4007. Shunt resistors: 0.1R*2 each side instead of 0.47/2W.

Transformer: primary: 4T+4T * 20strands of 33 SWG [ winding type: bifiller], secondary: 64T+64T * 1 strands of 22 SWG, insulation: 3mm, core size: EE50.

Sink area: 6*5*3.25cm in each channel.

Remember again, the converter works so smooth below 100W. Heated only at over 200W load. Output voltage: 318VDC at no-load and 315V at load, even at 200W load.


Expecting help from experts...

Thanks

I've solved it last night. I modified the transformer. now its working fine.

Hello,
I just jump into this thread looking for a solution to a problem. Do you mind sharing your circuit diagram? I am struggling with a 500 VDC PSU.

Saskia