Electrical Engineering ⇒ Topic : Action of Diode

Action of Diode

When the filament is heated, it emits the electrons shown in Figure (a). The electrons form a group of negative charges in the free space above it and build an electron cloud. The region containing the electron cloud is called the space charge and this region is highly negative with respect to the cathode. The additional electrons are emitted by the cathode and at the same time an equal number of electrons fall back and recapture so that the number of electrons constituting the space charge remains constant. If its plate potential is maintained at zero potential, very few electrons with high kinetic energy will be able to reach the plate and the plate current is very small. If the plate potential is made positive, the electrons will be attracted towards the plate. As the potential of the plate is made more and more positive, the strength of the plate current will be increasing. A stage will be obtained when all the electrons emitted from cathode will be attracted by the plate. This is called the saturation stage and the plate current is called the saturation current. The plot of plate current versus plate voltage is shown in Figure (b).

                                                   (a)                                                                     (b)

                                                                       figure

From Figure (b), it is clear that higher the temperature of the cathode, greater is the rate of emission of electrons and hence saturation current