Flyback converter

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Hi,
I designed a 24V,2.5A flyback converter by PI Expert with 230V input. With no load the voltage of output is 37V instead of 24V and when I connect a load ( 3kohm/1W resistor) to output, output voltage drop down to 25V and then increase to 37V and again drop down and increase this happens frequently, and transformer makes noise sometimes approximately every two seconds it makes a noise. I don't know what is the problem .
I attached the schematic.
Thanks,
Best Regards.

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TOPSwitch-HX_PIDesign.pdf52.37 KB

This sort of power supply behavior 1) output out of regulation 2) supply output collapses and triggers autorestart with light load - commonly occurs when the transformer is reverse phased. Check the anode of your output diode (D3) with respect to output return using an oscilloscope. The anode of D3 should go negative when the U1 primary switch is on, then fly back to a positive pulse with a constant value. If this is not the case, then the transformer is reverse phased. The bias rectifier (D2) should be also examined to see if it is correctly phased. Reverse phasing on either the output or bias winding can cause the condition you're seeing.

Thanks for your reply

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