A: When it’s a Transistor or a Zener diode.
What is a Diode?
A diode allows an electric current to pass in one direction while blocking current in the opposite direction. It works using a doped silicon P-N Junction.
If you put two diodes in combination, it can be used to a positive effect; for example, a diode bridge uses an arrangement of four diodes to convert alternating current to direct current.
However, when you put the diode components, two P-N junctions back to back, rather than controlling the direction of current flow, you can get an amplification effect.
In addition, A Zener Diode is a single P-N junction that allows current to flow in the forward direction in the same manner as an ideal diode, but also permits it to flow in the reverse direction when an avalanche breakdown occurs. Note the term Avalanche – a sudden and overwhelming effect.
How does this relate to Data Diodes? Data Diodes are designed to do the data equivalent of silicon diodes: A data diode allows data to pass in one direction while blocking data flows in the opposite direction.
If you start to put combinations of data diodes together (like a diode bridge), you can get a very positive effect, as Nexor demonstrate in our remote camera control solution.
However, if you put diodes back to back, you may get a different effect to the one you expected.
Beware of diodes that are not really diodes, you might just get a transistor and amplify your data leakage or a Zener diode where you get sudden and overwhelming data loss.
This is sometimes referred to as the Lirpa Loof effect.