Kind Of Diode

Diode Description

fig.1 - Diodes

            Diode, electronic device that allows the passage of current in only one direction. How things evolved … The first such devices were vacuum-tube diodes, consisting of an evacuated glass or steel envelope containing two electrodes - a cathode and an anode. Because electrons can flow in only one direction, from cathode to anode, the vacuum-tube diode could be used as a rectifier . The diodes most commonly used in electronic circuits today are semiconductor diodes. The simplest of these, the germanium point-contact diode, dates from the early days of radio, when the received radio signal was detected by means of a germanium crystal and a fine, pointed wire that rested on it. In modern germanium (or silicon) point-contact diodes, the wire and a tiny crystal plate are mounted inside a small glass tube and connected to two wires that are fused into the ends of the tube.

What can a diode do …

          Because this electronic device allows passage of current in only one direction , it is used in rectification, process of converting an alternating current (AC), which flows back and forth in a circuit, to direct current (DC), which flows only in one direction. Light-emitting diodes are used in many common devices, such as the tuning indicator on a radio. Any number from 0 to 9 may be displayed on a seven-segment arrangement (an arrangement often used on calculators and digital watches), in which each LED lights one segment.

fig.2 - Seven segment arrangement

In this picture 3 zeros from a digital display

Types of diodes

fig.4 - LED

        

           Junction-type diodes consist of a junction of two different kinds of semiconductor material. The Zener diode is a special junction-type diode, using silicon, in which the voltage across the junction is independent of the current through the junction. Because of this characteristic, Zener diodes are used as voltage regulators. Another special junction-type diode is used in solar cells; a voltage appears spontaneously when the junction is illuminated.

Understanding N-TYPE AND P-TYPE semiconductors

A germanium or silicon crystal, containing donor-impurity atoms, is called a negative, or n-type, semiconductor to indicate the presence of excess negatively charged electrons. The use of an acceptor impurity produces a positive, or p-type, semiconductor, so called because of the presence of positively charged holes.

A single crystal containing both n-type and p-type regions may be prepared by introducing the donor and acceptor impurities into molten germanium or silicon in a crucible at different stages of crystal formation. The resultant crystal has two distinct regions of n-type and p-type material, and the boundary joining the two areas is known as an n-p junction. Such a junction may be produced also by placing a piece of donor-impurity material against the surface of a p-type crystal or a piece of acceptor-impurity material against an n-type crystal and applying heat to diffuse the impurity atoms through the outer layer.

fig.4 - Understanding the n-p junction