Guess this question has been broth up before:
I have read the switching psu pdf, etc. just wondering what’s wrong with connecting a regulated psu to J1 with the 7805 not connected, why use J2?, would not the rectifier and caps, just remove any extra ripple? Is this wrong?
Nikolai
why use J2?, would not the rectifier and caps, just remove any extra ripple? Is this wrong?
The caps are no issue… but the rectifier will lower your voltage by 2 times the forward voltage of the diodes.
So depending on the rectifier, you will get something between 3.6V and 4,4V instead of 5V.
Raphael
Ahhh!
Thank you for clearing this!, I learn so much from this forum 
Nikolai