How do high voltage diodes work?

[Shrek]

One can make a high voltage diode by stringing low voltage diodes in series…
BUT the forward voltage drop gets increased.

How do real high voltage diodes keep the same low forward drop of just over
a volt regardless of the reverse voltage they can sustain?

 

[Bill_Bright]

Not sure "just over a volt" is typical. But for sure, the depletion zone is designed to handle any expected reverse voltage to maintain that 0 conductivity - at least until the breakdown voltage limit is hit. Hopefully, that breakdown threshold is well above any expected voltage. If not, the circuit was poorly designed, or the device or the circuit has a fault.

I did find this - fairly general but applicable: https://www.electricity-magnetism.org/high-voltage-diodes/

Oh, and of course, heat is always a factor.

 

[Shrek]

I think you are right, just one P-N junction with a huge depletion zone; many thanks.

I am working on a 500W EVGA power supply that has room for and seems to need a second rectifier bridge
EVGA 500W Review - Another One (PSU) Bites the Dust - YouTube

I belive they sometimes intentionally run the diodes hot to reduce losses, but given this failure I'll install a second bridge.