for a discrete diode in a separate package (not integrated into an IC)
the relative voltage (difference between the two connections) is all that matters

bki wrote on May 6^th, 2015, 2:00am:


It's the same in principle, but can be quite different in practice.  You can run an IC off whatever voltages you wish, as long as the difference between the voltages you define as VDD and VSS is within allowed limits.

The challenge here is that typically an IC is connected to a ground plane on a PCB so now instead of just a diode operating at elevated voltages you have a whole system floating.  That can lead you to a whole world of hurt regarding proper grounding and EMI considerations (and that's just for starters).  People do this, but you have to think it through.