What is a diode?
Diode: A diode is an electronic component that allows the flow of electric current only in one direction. For allowing current only in one direction it is used in the rectification process where the AC signals are converted into DC signals.
In electronics, different types of diodes are used for different applications. They are used as a voltage regulator, oscillators, switches, signal mixtures, signal limiters, signal modulators, and demodulators, etc. In this tutorial, I am going to unlock the details of different types of diodes.
There are different types of diodes are available for use in electronics design such as
1. Diode valve.
2. PN junction diode.
3. Zener diode.
4. Light-emitting diode(LED).
5. Photodiode.
6. Schottky diode.
7. Shockley diode.
8. Tunnel diode.
9. Varactor diode.
10. Avalanche diode.
1. Diode valve
A diode valve is the simplest vacuum tube. It consists of two electrodes called anode and cathode and they have placed insight a highly evacuated glass or metallic bulb. The cathode may be directly or indirectly heated type. A coaxial filament is used to heat the cylindrical cathode.
Electrons emitted from the cathode by the thermionic process are attracted towards the plate when it is kept at a positive potential with respect to the cathode and a current is obtained. It is called a diode because it has two electrodes.
As the current in it always flows in one direction it is called a valve in analogy with a pressure valve which allows fluid to flow only in one direction.
2. PN junction diode
A PN junction diode is a two-terminal electronic component that allows the flow of electric current only in one direction. In the forward biased condition, the diode allows the flow of the electric current but in the reverse biased condition, it blocks the flow of electric current.
PN junction diodes are made with semiconductors such as Germanium(Ge) and Silicon(Si). The n-type semiconductors where the majority carriers are free electrons and The p-type semiconductors where the majority carriers are holes, when they are joined to each other and make a PN junction then a diode is formed called PN junction diode. It is used as a rectifier, and also in the low current application, power applications, etc.
3. Zener diode
A Zener diode is a special type of diode which operates in the Zener breakdown region. It is heavily doped diode then the normal PN junction diodes. Heavily dopped means the high levels impurities are added to the material for making it more conductive.
It has a very thin depletion region, so it allows more electric current than the normal PN junction diodes. Basically, the Zener diode is used to protect the electronic circuit. Other applications of the Zener diode are it is used in voltage stabilizer and waveshaping.
4. Light Emitting Diode(LED)
A Light Emitting Diode(LED) is an electronic component that can emit light when the electric current is passed through it. LEDs are made with semiconductors. When the electrons in the semiconductor recombine withe holes then it released energy in the form of photons.
The color of the light is determined by the energy required for electrons to cross the energy bandgap of the semiconductors. Early LEDs produced only red light, but modern LEDs are made like that they can produce different colors such as yellow, green, blue. Basically, LEDs are used for indicator( such as power on/off lights) on the electronic devices.
Other applications of the LEDs are in electronic signs, clock displays, and flashlights. The LEDs are consumed very low energy than the old bulb, CFL, so it is largely used in lighting purposes.
5. Photodiode
A photodiode is a type of semiconductor device which converts the light energy to the electrical current. The photodiode absorbed photons from sunlight and make it is an electrical current. When the diode in dark no current will flow, but in light, the current flow from the cathode to the anode.
It allows current to flow only in one direction that means it produced DC current only. The photodiode contains an optical filter that allows light to reach the sensitive part of the device and may have large or small surface areas. In the solar cell, a large area photodiode is used to produce electricity.
6. Schottky diode
Schottky diode is a metal-semiconductor junction diode which operates in the lower forward voltage. For this lower forward voltage requirement, it allows higher switching speed and better efficiency. For this reason, it used in high-speed switching applications.
And also it is widely used in radio frequency applications. In a normal PN junction diode, the p-type and n-type semiconductor is used to make the PN junction.
In the Schottky diode, the p-type semiconductor is replaced by metals such as aluminum or platinum. The name Schottky comes from the German physicist Walter H. Schottky. The Schottky diode is also known as the Schottky barrier diode or hot carrier diode.
7. Shockley diode
Shockley diode is a four-layer semiconductor diode known as PNPN diode. The Shockley diode named after its inventor William Shockley. This type of diode is made with a set of interconnected bipolar transistors(one PNP and other NPN).
The last NP part of the PNP transistor is connected with the NP part of the NPN transistor. The Shockley diode is used as a trigger switch for silicon control rectifier, relaxation oscillator(sawtooth oscillator) and also it is used as an audio amplifier.
8. Tunnel diode
Tunnel diode is a heavily doped PN junction diode that has negative resistance due to tunneling. For this negative resistance the current decreases with increasing the voltage across the diode. The tunneling diode was invented by Leo Esaki when he working in quantum mechanics about electron tunneling effect.
The diode is used as a very fast switching device in computers and used as a logic storage memory device. and also it is used in high-frequency oscillators, amplifiers, and FM receiver.
9. Varactor diode
Varactor is a type of PN junction diode that has the capacitance which varies with varying the reverse-biased voltage. It operates only in reverse-biased voltage and acts as a variable capacitor.
The varactor diode is also known as varicap diode, tuning diode, and variable capacitance diode. The varactor diode is used in frequency multiplier and also it is used in parametric amplifier and voltage-controlled oscillators.
10. Avalanche diode
Avalanche diode is a special type of semiconductor diode which operates in the avalanche breakdown region at a specified reverse-biased voltage. It is similar to Zener diode but the doping level in the avalanche diode differs from Zener diode.
It is made of silicon or other semiconductor materials. The avalanche diode is lightly dopped then the Zener diode so the width of the depletion region is wider than the Zener diode.
Avalanche diodes are used to protect the electrical system from excess voltage. so it is used as a relief valve that controls the pressure in the system. And also it is used as a white noise generator.
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