This is a Coutant/TDK Lambda MML400 series switching power supply configuration 24G (24VDC nominal 15A 400W max).
What I simply can not quite understand is how the feedback from the secondary circuits get to the primary switching circuits.
Typically, a switchmode power supply would use either a small transformer or opto-isolator to provide an electrically isolated feedback signal, necessary to obtain voltage regulation.
However, this power supply has neither. The ONLY connection between the secondary circuits to the rest of the power supply is through the main transformer's secondary windings, represented by A, B, and C on the picture. B is the center tap of the transformer secondary.
I can not find any service manuals or schematics for this power supply online.
The only major power-handling components on the secondary side are the usual schottky diode and filter inductor and capacitors. So there's no further voltage regulation done on the secondary side.
There are no surface mount components on the backside of the PCB on the secondary side. The only components on the other side of the board, that can't be seen in the picture, are the schottky diode, capacitors, and a few flameproof resistors. The LM393D ICs that can be seen, are dual differential comparators according to the datasheet. Without reverse-engineering the whole circuit, what sort of voodoo magic is going on here?
Clearly, there has to be some form of feedback across the isolated gap between primary and secondary (otherwise there would be no way of obtaining precise voltage regulation), but how are they doing it? Any ideas?