Dioder is a semiconductor device with two terminals, typically allowing the flow of current in one direction only. Diodes allow current to flow when the anode is positive in relation to the cathode.
It is sometimes useful to summarise the different types of diode that are available. Some of the categories may overlap, but the various definitions may help to narrow the field down and provide an overview of the different diode types that are available.
1. PN Junction diode
The ordinary diode used in most applications from rectifiers to clippers.
2. Zener diode
A diode with a high reverse breakdown voltage used as a voltage regulator.
A diode which emits electron-hole pairs when exposed to light used to make detectors and solar cells among other things.
4. Light-Emitting Diode (LED)
The inverse of the photodiode, it gives out the light when driven by electricity. Its low power consumption makes it an attractive lighting source.
5. Tunnel diode
A diode capable of very high-speed operation due to the quantum tunneling effect. It is used in high-frequency applications.
6. Varactor diode
A diode whose capacitance can be varied with applied voltage.
7. Schottky Diode
It is a diode which is used to maintain a fixed voltage of 0.15 – 0.45 Volts. It is used mainly to speed up transistor switching. The Schottky diode has a lower voltage across its terminals when compared to other diodes as it consists of a metal-semiconductor junction as opposed to a P-N junction in others.
It is connected across the base and collector of an NPN transistor to maintain a constant voltage (as shown in the figure). This prevents the transistor from going into saturation which would slow down switching. These high-speed transistors are called Schottky transistors.
The more important point is that the Schottky diode has a lower reverse recovery time compared to the transistor and can switch back faster. Without this feature, the diode would impede the transistor’s operation itself. But the Schottky diode enables faster switching as it switches faster than the transistor it is connected to.