diode (thing)

The normal diode is an electronic device that lets electronic current flow in one direction but not the other. The first diodes were electron tubes. These were relatively big and not very efficient. Later a smaller kind of diode was developed, it consisted of a metal and a metaloxide. the metal/metaloxside is probably the easyest diode to make, all you need is to put a pice of metal against an oxidized metal and you have a simple diode. Eventualy the tubes and metal/metaloxide diodes was replaced in most devices by semiconductors.

The most used semiconductor in diodes are silicon, but germanium and gallium is also used. The basic diode consists of a positively doped and a negatively doped material on a semiconducting substrate. The place the two meet is called a PN junction.

The silicon diode is the most used today. It has a forward voltage drop from approximatly 0.7 volt for a small signal diode, to 1V or more for a high-power rectifier diode.

The fast recovery diode is a diode that switches faster between a conducting and nonconducting state. their switching time may be as low as 1ns.

The Zener diode functions as a normal diode in the forward direction. Also when connected backwards it will seem as a normal diode, until a spesific voltage is reached, then it starts to conduct. The zener diode is must allways be used in series with a resistor or it'll be fried. When in series with a resistor the voltage over the diode is stable at the zener voltage, and therefore the zener is used in voltage stabilizer circiuts.

The Avalanche diode is used for similar purposes as the zener diode but is available for voltages from 100v to 300v

The germanium diode has a voltage drop between 0.2v and 0.5v. It was dominant before the 1960s, when the silicon diod became available , but are still in use in some radio and video detector circiuts.

Schottky diode: This diode can in most cases replace the germanium diode. It has a voltage drop of about 0.4v, and fast switching. This means it's a good choice for high frequency applications.


The capacitancediode(varactor/varicaps): All diodes have a backwards capacitance that falls when the voltage rises, but the capacitance diod is optimized for this. These diodes are used in radios instead of the variable capacitor. Without this component we might not have the pocket radio with digital tuning.

The Light emitting diode(LED) is a diode that, as the name suggests, sends out light. They are available in just about any colour from infra red to blue(blue LEDs are still expensive so they are not much used). the forward voltage drop of a LED is between 1.4v and 3v depending on type.

The LASER diode. This is a more refined type of LED that emitts LASER light. By the addition of an appropriate lens (collimator) you will get a thin high intencity beam. The LASER diode is available in power from 1 mW to 10 mW.