Diodes

[greyark]

I need to know a little more about Thermionic diodes. Can anyone help?

[buildersmate]

They conduct electricity in one direction only - meaning they offer a high resistance to the flow of current in one direction but a low resistance in the other. In that way they can be used to rectify an AC source into a DC source.

[greyark]

Thanks

[chakka35]

buildersmate's answer is correct but it applies to any diode, including semiconductors.

A thermionic diode has a glowing filament which either emits electrons in its own right or, more usually, heats a more efficient emitter of electrons known as the cathode.
These electrons are captured by a metal plate - the anode - which is at a positive potential compared with the cathode. This gives rise to a current flow across the vacuum that exists between the two electrodes.

It is a one-way action - the positive anode collects negative electrons. There is no way that the action can work in reverse.