The Diode

Author: N.H. Crowhurst

The first electronic amplifiers used a tube type called a triode because it has three active electrodes. The earliest triodes started with an addition to the diode (two-electrode) tube which used a filament of wire heated by passing a current through it and a piece of cold metal called a plate. These elements were placed in a space from which all the air was evacuated, usually enclosed by a glass envelope.

Construction and action of a diode

The diode rectifies current (allows it to pass only one direction). By electron theory, this action is explained as follows: Heating the filament causes the electrons in it to become very agitated, and they leave its surface freely in a vacuum. Electrons have a negative charge, hence if a positive change is present in the vacuum, the electrons will be drawn to it, reaching the jposi-tive electrode. If, however, the potential on the plate is negative, it will repel the electrons (like charges repel, unlike charges attract), so they will stay near the filament, and no further charge can be taken by the plate. Therefore, when the plate Is negative, no charge passes, which means that no current flows through the tube.