What is a P-N Junction DIODE?
A
Diode is a unidirectional device permitting the easy current flow in one
direction but resisting the flow in opposite direction. A semiconductor diode
is simply a P-N junction with connecting leads or terminals on its two sides. P-N
junction is also called the crystal diode because it is grown out of crystal. A
P-N junction may get open circuited or short circuited and the best instrument
for testing a P-N junction is an ohmmeter. An ideal P-N junction diode is a two terminal polarity sensitive
device that offers zero resistance, when it is forward biased and infinite
resistance if reverse biased. So the diode conducts only in forward biasing
condition.
How a P-N Junction Diode works?
The
current through the diode will be in bipolar in character, because it is made
up of both positive and negative charge carriers and the total current is same
throughout the device, but the proportion of current due to holes and that due
to electrons varies with the distance.
In
the forward biased condition the diode current increases exponentially with the
increase in voltage across the diode. Diode current, when the diode is forward
biased, is given by
I = I0(eV/Vt – 1)
There
are two mechanisms by which the breakdown can occur at a reverse biased P-N
junction.
- AVALANCHE BREAKDOWN
- ZENER BREAKDOWN
The
breakdown phenomenon is reversible and harmless so long as the safe operating temperature
is maintained.
When
a P-N junction is switched from forward bias to reverse bias, the stored excess
minority carrier charge must be removed from the junction. The time required to
remove this charge is called the storage time and it is a limiting factor in
the speed of switching a diode.
APPLICATIONS OF P-N JUNCTION DIODES
- Can be used as rectifier in DC Power Supplies.
- In Demodulation or Detector Circuits.
- In clamping networks used as DC Restorers
- In clipping circuits used for waveform generation.
- As switches in digital logic circuits.
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