If you look at the right hand drawing, the middle two diodes in the left hand side of the are effectively back to back, thus connecting the centre tap to the ground, with a drop of about 0.7V, AC.
Worse, if you look at the right hand pair, when the lower winding is positive, (and thus the upper one negative), they are in series across the windings, effectively shorting them out!
If you have a centre tapped secondary, use 1 bridge, AC1 and AC2 to the outer leads, and connect the centre tap to ground.
If you have two seperate secondaries, (or two seperate tramsformers), connect a bridge to each, and then common a positive and a negative to ground.
HELP! what is a decent free or cheap program I can use to jot down quick circuit diagrams ? I’ve had a go in eagle, but I need more practice…
is OK if you only have a single secondary winding and need plus and minus voltages. It won’t suply as much current as a centre tapped secondary, because it’s only half wave rectifying the AC for each regulator.
Once I can get up to speed on something that will let me make decent schematics for the web, I’ll try and do a proper write up.
I’ve updated the OPL3 PSU schematic, so that it only uses a single bridge rectifier. I think that I never found this issue by myself, since I’m using transformers with seperate secondaries - and I’m not sure, if I connected the two middle AC lines together. I will check this once I open the case of my MBFM again.
The PSU of JD Sleep looks like a good alternative solution for people, who have a single secondary transformer lying around which they want to re-use for the AOUT or OPL3 module.
A wiki page about this topic would be great! I would add a link to this page from ucapps.de, so that everybody can read more about different variations.
Freeware schematic drawing tool: I’m using xcircuit since more than 10 years now. I don’t know if there are better tools in the meantime, but this one works under different operating systems, which is a big advantage.
