Different ICs have difference output.

4 posts / 0 new


I have made non-isolated power supply using LNK409 with following config.

IN : 185-240V
Ou : 70V 400mA

Power Factor : 0.981
Efficiency : 88.5%

This power supply can also output upto 50Watts. I am using it for 30W output.

But When I change the IC it will change the output upto 20%. Also tried changing different IC for Different PCB.
But the problem is LNK409.
I note that there is number on IC like 1113,1112,1046...etc
Output changes with these number.

It could be due to some noisy traces affecting the reference and feedback. Please double check the layout first. Please also send, if possible, your schematic so we can further analyze.


I followed your PCB layout guidelines and Also tried some different layouts to sortout this issue.


Anyways, I have uploaded PCB layout and circuit Diagram.


Let me know if you find any issue related pcb layout.

Please try to improve the routing of the FB trace such as avoid routing underneath the transformer. Try to eliminate the crossing path between the FB trace and Vpin trace.

Lastly, please verify the calculation of IFB (since the values are not stated in the schematic) and make sure it's within 100 to 200uA.