Newly designed 5v 1A smps output drop 200mA load connected to it. No load condition it show 5v. When load is connected drop to 3v.
How to fix it?
P1&P2_Input 240v AC
P3&P4_Primary Winding
P6&P5_Auxiliary winding
P7&P8_Secondary Winding
P9&P10_Filter capacitor 10uf,400v
P11&P12_Output 5v 1A
Switching IC is AP8012 Not VIPER 22A
Circuit Attached here

 

Where did you get the application reference for your circuit?
I checked the datasheet of AP8012 or AP8012-ait, there is no any resistor in series with the phototransistor of U2(LTV-356T) as R3.

 

if there is no R3 output voltage goes upto 21. same time feedback current should be 3mA.so i put 10K resistor

 

if there is no R3 output voltage goes upto 21. same time feedback current should be 3mA.so i put 10K resistor

Does 3mA will be over current or exceed the current you want?
Please check the page 5 of AP8012. it shown that the comp pin of internal block already has a R1 inside.

 

when i was bypassing the r3 output voltage goes high ... Now what can i do

 

D2(1N4148) change to 1N4007 and shorted the L1(10uH) to try

 

D2 should be high frequency diode. I was already try bypass the L1. Nothing happen.

 

AP8012 sample board 12V/250 mA -- it used 1N4007 inside on page 2, to check the transformer and comparing with yours.
Choosing Standard Recovery Diode or Ultra-Fast Diode in Snubber_snva744.pdf -- What 1N4007 can do may breaking your thought.

 

Your current is limited by the pulse transformer, D3, or L1, the chip has no facility to monitor current limit, only Voltage feedback .

 

AP8012 sample board 12V/250 mA -- it used 1N4007 inside on page 2, to check the transformer and comparing with yours.
Choosing Standard Recovery Diode or Ultra-Fast Diode in Snubber_snva744.pdf -- What 1N4007 can do may breaking your thought.

I replaced the 1n4148 to 1n4007 but still same result.