So we need a differential "share" bus....thats why this is needed
That is a totally different situation.
To start with, the drivers to the common bus must be either current controlled, or the bus drive connections all via equal resistances to balance them and limit current. Presumably the bus voltage should be the mean of all individual devices on it?
It cannot be simple voltage from opamps as you have shown, otherwise some drivers will be overloaded and the output unpredictable.
OK; Looking at the UC3902, its a different configuration again:
The
only drive out is via a diode to bus positive, so there is no contention. That just drives the bus with a voltage proportional to current, so whichever supply has the highest load is the one driving via its diode.
That will have some 0-100% load scaling, apparently 10V if the supply voltage permits, and all devices use the voltage read back to set the percentage of individual maximum current they provide.
The bus negative is not active or driven in any way, it's purely a shared ground reference for the differential amps.
The whole lot uses two, four-resistor differential amps (plus a diode) for all that.
The rest of the device is for the load percentage control.