Output voltage not stabilizing.

Thanks for Posting your question into forum. Could you please clearly explain which device you used, we don't have device name EP-33. Did you use any of our Design Example reports as a reference for building the Power supplies?
Regards,
PI-KSAN

I assume poster means circuit according to EPR-33 on your website regarding EP-33 circuit.

EPR-33 is an old application note. I have attached the same. The circuite is according to EPR-33. Device used is TOP247Y.

You must first verify that feedback system is working. Use external supply and verify that LM431 circuit will vary the LED current over the required range as voltage is varied.

Then verify opto coupler is working and that you have sufficient control current on primary side. You may have to disconnect from topswitch and use external supply.

If feedback works, then most likely either current limit is incorrect, or transformer/recitifier/filter has a problem. There is not much else that can be wrong, the topswitch has most of the primary side control circuits inside.

Be certain that the transformer is connected correctly, so that output is REVERSE BIASED when topswitch mosfet is "on".

Verify that duty cycle varies with load. If drain node duty cycle goes to maximum, transformer etc most likely has a problem. Because output is not going to correct value, the feedback should command maximum duty in an attempt to correct the output.

If duty cycle does not go to maximum, then check current limit.

When troubleshooting a feedback system, you generally must look to see if feedback is working, if it varies the controlled function correctly in amplitude and direction. You may often need to open the loop to test that in a thorough manner.

Thanks Jtiers for answering in the forum. Shrikanth please follow as Jtiers said and let us know if you see any issues.

Regards,
PI-KSAN