Different Types of Special Diodes

A light emitting diode is one of the common types of special diodes.LED image by URIO from Fotolia.com

In electronics, diodes allow current to flow in a single direction. You can use these semiconductor devices to control the on/off flow of current or to convert alternating current to direct current. Special types of diodes have different applications and work differently than a typical diode. Learn about the different types of special diodes in order to know when to use each one for an electrionics project.

Light Emitting Diode

You can find light emitting diodes, or LEDs, in many types of electronics. LEDs use energy flowing through different chemicals or gases to produce different colors of light. The original LEDs used hydrogen gas for a red light but now come in a variety of colors. The most common type of LED today uses a compound called gallium-arsenide-phosphide to produce a bright red light. LEDs require a forward bias to produce light and you can wire them in parallel or in series.

You can find Schottky diodes in rectifier applications and radio frequency applications. They have a lower forward voltage drop and faster switching times than the standard PN junction diodes. Manufacturers also use Schottky diodes in computer circuits because the diode can perform well at high speeds and dissipates less power than other diodes. Schottky diodes use a metal-to-semiconductor connection to provide this high performance.

Photodiodes work in the opposite away as light emitting diodes in that they detect instead of produce light. Photodiodes also work on a reverse bias as opposed to the forward bias of other diodes. When a photodiode detects either infrared, ultraviolet or visible light, it generates an electronic signal. Most photodiodes are made of silicon and work faster than other light absorbing diodes such as solar cells.

A less common type of special diode, the tunnel diode, is known for its ability to switch quickly between the maximum and minimum levels of current that can pass through the diode. This diode operates on the phenomenon of resonant tunneling. This means that even with applying increasing voltage to the diode, at some point the current will decrease instead of increasing. Tunnel diodes resist temperature fluctuations better than other diodes, and manufacturers use tunnel diodes for microwave applications.

The varactor diode, or varicap diode, has applications in radio frequency devices and frequency multiplier circuits. The diode can serve as a capacitor in reverse bias situations --- the reverse bias creates an insulated section and changing the bias will alter the level of capacitance. Some types of varactor diodes provide only a small variance in capacitance while others produce a wider range.