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.

if the Tx Lpri is too high you will not get the power you are seeking ....