Diode

A diode can be thought of as the electronic version of a one-way valve. By restricting the direction of movement of charge carriers, it allows an electric current to flow in one direction, but essentially blocks it in the opposite direction.

Diode technology

The first diodes were vacuum tube devices (also known as thermionic valves), arrangements of electrodes surrounded by a vacuum within a glass envelope, similar in appearance to incandescent light bulbs. The arrangement of a filament and plate as a diode was invented in 1904 by John Ambrose Fleming (scientific adviser to the Marconi company) based on an observation by Thomas Edison. Like light bulbs, vacuum tube diodes have a filament through which current is passed, heating the filament. When heated, the filament can emit electrons into the vacuum. These electrons are electrostatically drawn to a positively charged outer metal electrode called the anode, or "plate". Few electrons flow from the plate back toward the filament, even if the charge on the plate is made negative, because the plate is not heated and therefore does not eject many electrons by thermionic emission.

Related Topics:
Vacuum tube - Thermionic valve - Light bulb - 1904 - John Ambrose Fleming - Marconi - Thomas Edison - Filament - Anode - Thermionic emission

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Although vacuum tube diodes are still used for a few specialized applications, most modern diodes are based on semiconductor p-n junctions. In a p-n diode, conventional current can flow from the p-type side (the anode) to the n-type side (the cathode), but not in the opposite direction. When the diode is reverse-biased, the charge carriers are pulled away from the center of the device, creating a depletion region.

Related Topics:
Semiconductor - P-n junction - Anode - Cathode - Depletion region

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