DIODE
A Diode is a uni-directional device consisting of two
terminals namely positive and negative. The diode is a semi-conductor device
which is used in several electronic applications.
*What is semi-conductor?
To know about semiconductor, let us learn about the atom. In
earlier sessions you learnt about atom. Atom is made up of tiny particles. The
atom consists of sub-atomic particles like proton, electron and neutron. The
valency of an element is explained based
on the number of electrons present in outermost shell.
Based on the valency
electrons the material is classified into three types
1. Conductor
2. Insulator
3. Semi conductor
* In conductor there are many number of electrons which are
free form bonding (Free electrons) these electrons carries the electric charge
from one place to another.
* In Insulator there is absence of free electrons. So there
is no charge carries
*In semiconductor the outermost electrons are half filled and
acts as partially conductor and partially Insulator.
The semi conductor elements are Silicon, Germanium etc.
>The diode is made up of Si or Ge based on conduction time
period and break down voltage.
Diode in Forward bias:
The below circuit shows the diode is connected in forward
bias with respect to battery and load resistance RL. we can say the
diode is in forward bias by connecting positive terminal of a battery to the positive terminal of diode.
>In forward bias the diode allows the electrons to flow
through it. The characteristics of diode is given below with two different
manufacturing.
The diode conduction period for “Ge” is less when compared to
“Si”. Hence in most cases “Ge” is used for diode.
Diode in reverse bias:
The below circuit shows the diode is connected in reverse
bias with respect to battery and load resistance. We can say the diode is
reverse bias by connecting positive terminal of battery to the negative
terminal of the diode.
>In reverse bias the diode blocks the electrons flow, it
does not allows the electrons to move through it.
>The characteristics of diode when connected in reverse
bias is given below:
From graph you can conclude that there is no conduction in
reverse bias.
*What is the mechanism inside the diode?
At first i stated diode is a semiconductor, every
semiconductor consists of depletion layer. Observe the below figure:
The figure about inner view of the diode. The diode is doped with p- type and n-type semiconductor.
In p-type holes are present whereas in n-type electrons are present.
At Initial position:
At initial position
it mean when there is no supply the electrons attracted towards the holes and
vice versa leads to the formation of depletion layer. This layer acts like a
wall for p-type and n-type.
At performing:
When diode is fed
with the supply the holes energized by an external supply and moves towards the
electrons from the depletion layer and fulfill the output.
Applications of diode:
Diodes perform best
in
1. Rectifier circuits
2. Radios
3. Speed control devices
4. Mobile charges.
Zener
diode
The diode which has ability to perform the operation in both
forward bias and reverse bias. The below circuit shows the zener diode
connections.
The characteristics obtained from zener diode is given below:
*What is the mechanism inside the zener diode?
The zener diode
has same constructional view like diode but the only difference is in p-type
semiconductors some electrons are located to carry the charge from one place to
another.
In forward
bias the action of zener diode is similar to diode but in case of reverse bias
the diode conducts sharply after some time. This phenomenon is named as break
down voltage. When the diode reaches break down voltage in reverse bias it
start conducting. This diode also conducts when there is change in current
direction.
Applications:
1. Used in voltage controllers
2. Mobile charges
3. shunt regulators
4. Voltmeters, Ammeters, Ohm meters.
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