What Is a Diode?
A diode is an electronic component that allows current to flow in only one direction. The most common type is a PN-type diode consisting of an N-type semiconductor and a P-type semiconductor.
N-type semiconductors are semiconductors with an excess of electrons compared to the positive charge of the nucleus. The extra electrons are called free electrons, which move from the negative to the positive side when voltage is applied.
When voltage is applied to a PN junction diode so that the P side is positive and the N side is negative, the holes that have moved to the negative side and the electrons that have moved to the positive side meet at the PN junction surface, and the electrons on the N side and holes on the P side combine and both disappear.
For that amount of time, electrons are supplied to the N side from the power supply, and electrons flow out of the P side to produce a hole, resulting in current flow from the P side to the N side. Conversely, if a negative voltage is applied to the P side and a positive voltage to the N side, the holes will move to the negative side and the electrons to the positive side, both on the opposite side of the junction surface, and no current will flow.
This characteristic of a diode that allows current to flow one way is used as a switch or rectifier.
Types of Diodes
There are various types of diodes, but the following six main types exist:
- Rectifier diodes
- Switching diodes
- Zener diodes
- Photodiodes
- Schottky barrier diodes
- Light Emitting Diodes
1. Rectifier Diodes
A rectifier diode converts alternating current to direct current by allowing current to flow in one direction and not in another, depending on the direction of voltage.
2. Switching Diode
A diode that functions as a switch with a feature that allows current to flow in only one direction. Compared to rectifier diodes, switching diodes are characterized by a shorter time from the on state to the off state.
3. Zener Diode
When a reverse voltage is applied to a diode, no current flows, but when the reverse voltage exceeds a certain voltage (Zener voltage), current flows in the reverse direction. Because it maintains a constant voltage regardless of the magnitude of the current, a Zener diode is sometimes called a constant-voltage diode.
4. Photodiode
A photodiode is a diode in which a small current flows in a constant direction when illuminated by light. It works in the opposite way to a light-emitting diode (LED).
5. Schottky Barrier Diode
A diode with a structure consisting of an N-type semiconductor and a metal junction instead of a PN junction. The time from the on-state to the off-state is very short, and they are used for high-speed switching operations.
6. Light-Emitting Diode
These diodes are well known as LEDs. When a forward voltage is applied, electrons and holes combine and are annihilated at the PN bonding plane, and the difference in energy before and after this happens is emitted as light. The color of the emitted light differs depending on the compound that makes up the semiconductor.
Diode Characteristics
Diodes have a variety of electrical characteristics, including V-I characteristics, which express the relationship between applied voltage and flowing current, reverse recovery time from diode on to off, maximum values of forward and reverse voltage that can be applied, maximum allowable values of forward and reverse currents, and power loss.
It is important to select a diode with appropriate characteristics according to the environment and conditions in which it will be used, as well as the type of diode for the application.
How to Use Diodes
Diodes are used in circuits that convert alternating current to direct current because of their property of conducting current in only one direction. They are also used in light-emitting diodes, which extract heat energy as light when coupled, and are therefore used in many electrical products. Light-emitting diodes have the property of emitting light from the PN junction when an electric current flows. Since they can emit light of various wavelengths depending on the material, they are used in TV screens and the projection part of infrared remote controls.
Since light-emitting diodes emit heat, they are widely used as energy-efficient LED lighting devices. Diodes are also used in AC adapters for various electrical devices. An AC power supply of 100 V is reduced to a voltage of 12 V or 6 V by a transformer and then to a smoothed direct current using a diode and a capacitor.