#Technical studies-study 2
PN junction Diodes are the basic semiconductor devices those allow current to flow only in one direction. This is a nonlinear device because the graph of its current and voltage is not a straight line. The reason is the barrier potential.
The P side of the diode is called Anode and the N side of the diode is called cathode. The diode symbol looks like an arrow that points from the P side to N side, from the anode to cathode.
In order to understand the diode working we need to supply voltage to the diode in different ways and find the differences. There are two types of diode biasing
Forward Bias of Diodes:
In forward bias the negative terminal of the voltage source is connected to cathode and the positive terminal is connected to anode.
Diode has a certain voltage up to which it acts as an insulator and on reaching that voltage it starts conducting. That voltage is called barrier potential. Barrier potential is also called knee voltage.
The knee voltage for silicon diode is 0.7V and for germanium diode is 0.3V.
When the source voltage is less than the barrier potential the free electrons are weak to cross the depletion layer.
When source voltage is greater than the barrier potential the free electrons pass through the depletion layer and diode starts conducting.
Reverse Bias of Diodes:
Connect the diode opposite way how connected in forward bias. Negative source terminal to the anode and positive source terminal to the cathode.
In this connection positive terminal attracts the free electrons and negative terminal attracts the holes. Because of this holes and free electrons flows away from the junction, so the depletion layer expands. In the mean time the newly created ions increase the potential difference across the depletion layer.
This process continuous until the potential difference is equal to the applied voltage.
There is a limit up to how much reverse voltage a diode can withstand before it destroys that voltage is called breakdown voltage.
VI Characteristics of Diode:
We can draw a graph by experimenting a diode and taking the readings of forward and reverse condition. The graph will be as shown above.
This graph shows the VI characteristics of diode. It shows that diodes are nonlinear devices.
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