What is a Diode?

A diode is a electronic component that lets electric current flow in only one direction.  The direction that current flows is called the forward direction while the other is the reverse direction.   The device has two terminals; the anode(+) and the cathode(-).   It is sometime referred to as a rectifier, since it can convert alternating current to direct current.  The diode was the first semiconductor device.   Today most diodes are made of silicon, but other semiconductors such as germanium and selenium are sometimes used.  Diodes characteristics can be tailored by varying the construction of their P-N junction.  This is exhibited in special purpose diodes that perform many different functions.  For example; specialized diodes are used to switch a circuit on or off (Switching Diodes), regulate voltage (Zener diodes), to electronically tune radio and TV receivers (varactor diodes), to generate radio frequency oscillations (tunnel diodes), and to produce light (light emitting diodes). Another type of diode is a Schottky barrier diode, used for high speed switching of UHF and other high frequency signals.   Diodes are possibly the third most used component next to resistors and capacitors and are most commonly used in low current power supplies.   Zener diodes are also extensively used, widely in devices to regulate voltages.  Light Emitting Diodes or LEDs produce light when current flows through them.  LEDs are used for things like lighted elements in computer systems, clocks, displays on microwaves and electronics, solar lighting and even some of the more modern designs in Christmas lights. 

The schematic symbol of a diode is shown below.


There is much much more to be learn about diodes and their characteristics.  Further study can be found in: "Compendium of Basic Electronics" by Wijono Hadikusumo.  To view more information on the book.  Click Here!

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