Diode Theory

Diodes are semiconductors that function as one-way valves. An ideal diode--called forward-biased--allows current to flow in one direction; a diode with current flow in the wrong direction is called reverse-biased.

Symbol

The symbol for a diode is an arrow. To indicate that the current is blocked when going in the opposite direction, the arrow has a bar at the pointed end.

Features

Many diodes are composed of silicon or germanium. Diodes will conduct when the forward voltage reaches a certain value, typically 0.6 volts for silicon.

Types

Small signal diodes are very common, typically performing as switches, regulating current or converting AC to DC. Other common types include LEDS, photodiodes and power rectifiers.

Special Types

Some diodes are made to conduct when they are reverse-biased. These include zeners, which are used to regulate voltage, and varactors, which behave like variable capacitors.

Uses

Diodes are found in many devices, such as surge protectors, lasers, light sources and sensors. They are also used to create power supplies and voltage doublers.

References

• Electronic Principles; Albert Malvino; 1999
• Getting Started in Electronics; Forrest Mims, III; 2000

Resources

• The Physics of Diodes

Photo Credit

Image by Flickr.com, courtesy of Erik Charlton