What is a diode? Describe the theory of diode operation. What is the application of it?
What are the types of diode? List them and draw their symbol.
Diode: When a p-type semiconductor and an n-type semiconductor are joined, the device is known as a diode. It has two terminals known as electrodes, one electrode each from p‐region and n‐region hence called diode (Di + electrode). A diode is an electrical component that allows current to flow in one direction only. It is made of two terminals, called the anode and the cathode, separated by a thin layer of material called the barrier. When voltage is applied to the diode, electrons flow from the cathode to the anode, allowing current to flow.
In the symbol of a diode, an arrowhead indicates the conventional current direction when it is forward biased. A diode allows current to flow in only one direction.
Forward bias :
- A p‐n junction is forward bias when a voltage is applied positive to the p‐side and negative to the n‐side.
- When a diode is connected in a forward bias, the negative terminal of the battery pushes the free electrons in the n‐region towards the junction. Similarly, the holes from the p‐region are repelled by the positive terminal of the battery and move towards the junction.
- A forward-biased junction has a narrow depletion region.
- The forward bias applied voltage V a , reduces the barrier potential across the junction from its original value V J to (V J –Va ) .
- The electric field reduces.
- The immobile ions in the depletion region reduce.
- A majority charge carrier current flows across a forward bias junction.
Reverse bias :
1. A p‐n junction is reverse bias when a voltage is applied positive to the n‐side and negative to the
2. When a diode is connected in a reverse bias, the negative terminal of the battery attracts the holes in the p‐region away from the junction. Similarly, the electrons from the n‐region are attracted by the positive terminal of the battery and move away from the junction.
3. A reverse-biased junction has a wide depletion region.
4. The reverse bias applied voltage aV a, increases the barrier potential across the junction from its
the original value V J to (V J + Va ) .
.5. The electric field increases.
6. The immobile ions in the depletion region increase.
7. A very small minority charge carrier current flows across a reverse bias junction.
Application of Diode:
1. Rectifiers are further classified as half-wave, full-wave, and bridge rectifiers.
2. Clipper circuits to remove unwanted portions of the waveform.
3. Clamper circuits to add DC level to the waveform.
4. Voltage multipliers such as voltage doubler, voltage triple, etc.
5. Various electronic and operational amplifier circuits such as voltage to current converters, log
and antilog amplifiers, precision rectifiers, protection circuits, etc.
Types of the diode and their symbol :
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