How is this rail grounded?

neclovek

New member
Hello, I recently got a bunch of AcBel API2P013 200W computer power supplies for free to screw around with and I want to modify one to be adjustable (mostly for fun and to learn something). I followed the board and draw a very crude schematic for one of them. first thing that got me is that the driver IC is UC3842B which would suggest that it’s a flyback supply (since the IC has no duty cycle limit) but that’s unusual for PC PSU + the rest of the circuit is clearly a forward supply design. The driving circuit is quite complex so I guess they somehow limit the duty cycle outside the IC? Does that even make any sense? Also I don’t quite understand the connection between 5V rectifier output and 12V winding (is that some funky way to create the 12V line ground?). If anyone could explain what’s going on with this design I would greatly appreciate it.
 

Attachments

  • 3E0738BE-90E4-414C-B660-A78938114065.jpeg
    3E0738BE-90E4-414C-B660-A78938114065.jpeg
    1.8 MB · Views: 4

Silvio

Member
Since the topology is flyback I think the winding arrangement may be more like the photo attached.
ATX smps.png
 

neclovek

New member
That doesn’t seem right though. I have triple checked it and my schematic is 100% correct. So basing on the way of rectification and the recuperation coil, I am assuming it is indeed a forward converter topology. But then both of these “mysteries” remain still unsolved.
 

neclovek

New member
I see, this weird 12V winding ground connection is apparently used in more than just this one PSU, but I can’t quite understand why...
 
Top