Current limit error uinig TNY274PN

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I have built the power supply with the schematic shown in the attached photo using TNY274PN. However, although it is designed for 2.5 A, and I used PI Expert for designing the transformer and carefully wound it, the power sully is not capable of providing 2.5 A. Actually for more than about 700 mA it goes to the hiccup mode and restarts frequently.
I am not experienced in using TinySwitches.
Thanks in advance.

Schematic121.64 KB

Hi Aliman,
Can you share with me the PIexpert computation that you used? I attached here schematic suggestion that you can used to check if the circuit will work properly.

Hi Jedidiah,
Thank you for your reply and suggestion.
Here is my PIexpert design. I should let you know that I used it merely for transformer calculations and other parts of the schematics are different and based on a schematic I found in application notes.
Thanks again. Looking forward to your reply.

Dear Jedidiah,
I just wanted to check your suggestion and found out that the circuit is already the same as you suggested and the top voltage of the divider for feedback is Vcc* which is after the diode and before the inductor. Do you mean another modification?

Hi Aliman,
Did you try to add resistor in between VCC and PC817? I attached the latest schematic with three modifications highlighted.

Also, can you convert your PIXLs into excel file? There should be an export option to convert it into excel file.

Schematic_suggestion.png338.84 KB