Output voltage dipping

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I an designing a SMPS 15V using a TOP261EN IC. I got design through PI expert online. But the output voltage is dipping when i connected to the load. What may be reason ?
Without load it is working fine. Even for 1A load also it is dipping. For more load it is dipping more voltage.
I have attached the schematic and i have changed the resistor R6 = R7 = 10M and R8=10K.
Can you please let me know in detail how it works

SMPS.pdf179.34 KB

Hi Naveen,

Check transformer Lmag value. Does the transformer gapped? Initially remove R6, R7 & R8 and short X node to gnd to remove reduced current limit. Next check the control pin voltage at no-load, does it stays above 5.8V or not with load? If not check the bias turns. Use C5 capacitor 16V or more rated voltage. Please share PI computation sheet.