A Guide to Diodes
A diode is an electronic device with two terminals that conduct current primarily in one direction. Diodes feature a low (ideally zero) resistance in one direction, and a high (ideally infinite) resistance in the opposite direction. Diodes have a broad range of uses and therefore come in many different types. The unique characteristics of the differing types allow them to perform a wide array of functions. In this blog, we will discuss the most common types of diodes.
LEDs are one of the most common types of diodes. They produce light when the diode allows the transfer of electric current between the electrodes. When the diode is turned on and the electrons combine with the holes, LEDS release energy in the form of light. The color of light emitted by an LED is dependent on the semiconductor’s energy gap. LEDs can produce wavelengths ranging from infrared to near ultraviolet.
Laser diodes are similar to LEDs, but produce a coherent light, making them slightly different. A laser is formed when an LED-like structure is enclosed within a resonant cavity formed by polishing the parallel end faces. Diodes of this type are regularly used in optical storage devices as well as high-speed optical communications.
An avalanche diode is a type of diode that conducts in the reverse direction when the reverse bias voltage exceeds the breakdown voltage. Their name comes from the avalanche-like effect that occurs when the reverse electric field across the P-N junction creates a wave of ionization like an avalanche, leading to a large current. Avalanche diodes are designed to break down at a predetermined reverse voltage without being destroyed.
Zener diodes offer a stable reference voltage and can be easily configured to conduct backwards. They are commonly used in tandem with switching diodes, wherein the two types are connected serially in opposing directions to balance the temperature coefficient to nearly zero. When many diodes are used together, it can form a diode bridge. This is an arrangement of four or more diodes in a bridge circuit configuration that provides the same output polarity for either input polarity.
Also known as varactor diodes, varicap diodes are used as voltage-controlled capacitors with a reverse bias that varies the width of the depletion relative the voltage across the diodes. Varicap diodes act as capacitors and capacitor plates formed by the extent of conduction regions in addition to the depletion region as the insulating dielectric.
Schottky diodes are a type of diode with a metal-to-metal semiconductor contact and a lower forward voltage drop than that of traditional P-N junction diodes. Schottky diodes can be used as low-loss rectifiers, though the reverse leaked current in diodes of this type is frequently higher than in other diodes.
The final type of diode is the tunnel diode. These are similar to the standard P-N junction apart from their doping levels, which are higher and have a more narrow depletion region. Tunneling is an effect that results from quantum mechanical effects as electrons pass through a potential barrier. Tunnel diodes are widely used in microwave applications.
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