Consolidated Leo posted:Stan: Something I've puzzled over is why a wall-wart is okay to use in this situation as opposed to other methods that convert AC to DC; like the bridge rectifier on the AC/DC buck converters. I understand that the bridge rectifier creates a separate ground that differs from the transformer ground.
Exactly! It's just that when using a bridge rectifier in the AC/DC buck converters the new/separate DC ground output was derived from the AC ground input and hence has a blood-line relationship. You cannot then marry the two ground signals as that would be electrically incestuous.
Not trying to be clever with the geneaology metaphor; it's just that I've previously tried to explain the technically precise requirement of galvanic isolation but doesn't seem to get the point across.
But what does a wall-wart do to make their DC ground compatible? I'm guessing that they use a single diode to produce half wave DC as you have pointed out previously. Then they are simply passing the AC ground through which makes it common with the AC ground from the transformer.
A wall-wart has an internal transformer which means its AC output has no blood-line relationship to the train transformer's AC output. So now, even if the wall-wart internally spawns a DC ground using a bridge rectifier, the wall wart's DC ground output still has no blood-line relationship to the AC ground of the train transformer. Hence the two signals can tie the knot and live happily thereafter. Note that you cannot access the internal AC ground of a wall-wart.
And what about DC from an old computer power supply? Is that not compatible? And how is it that you know this stuff?
A computer power supply has an internal transformer so it is like a wall-wart.
