DIODE

DIODE

What is Diode?

• Diode is specialized electronic component with two electrodes called the anode and the cathode.Diodes are basic unidirectional semiconductor devices  that  the current flow in one direction only and blocks the current flow in the opposite direction 
• It is active component
• It is constructed of a P and an N junction connected together.   
• The most common type of diode is a ‘silicon diode.’ It is enclosed in a glass cylinder with the dark band marking the cathode terminal. This line points towards the positive of a circuit. The opposite terminal is called the anode.
• Generally, diodes do not conduct until the voltage reaches approximately .6 volts, this is called the ‘threshold point’. If the current becomes too high the diode may crack or melt.

Operation of Diode:
       semiconductor diode connects to the external source in two ways.The process is known as biasing.

•   Forward biasing:positive terminal to the anode and negative terminal to the cathode.
•   Reverse biasing: positive terminal to the cathode and negative terminal to the anode. 

Forward biasing:
                 When the diode is forward biased, due to the negative terminal on the n-side, electrons from the n-side are pushed towards the p-region. Similarly due to positive voltage on the p-side of the diode, Holes from the p-region are pushed towards n-side.
               Due to this the electrons will start converting the positive ions in the p-region into neutral atoms and holes will start converting the negative ions in the n-region to neutral atoms. Hence width of the depletion region starts reducing due to reduction in the barrier potential.
              This keeps happening and at a certain point the depletion region collapses and there is no opposition to the flow of current. Hence large number of electrons and holes will cross the junction and make the electric current to flow from anode to cathode.
               Hence, forward biased electrical resistance of diode is very small and hence there is a small voltage drop  across it. Its value for silicon diode is about 0.7 V and germanium for 0.3V.

 
Reverse biasing:
             When the diode is reverse biased the hole from the p-side will get attracted towards the negative terminal of the supply and electrons from the n-side are attracted towards the positive terminal. 
             Hence the process of widening of the depletion region takes place and hence more and more opposition to the flow of  electric current takes place.
             Hence, ideally the reverse biased resistance of the diode is infinite and no electric current flows from the diode when it is reversed biased. 

Characteristics of diode:
 
Application of Diode:

• Rectifiers
• Signal limiters
• Voltage regulators
• Switches
• Signal modulators
• Signal mixers
• Signal demodulator, and Oscillators.