Invented in 1904 by John Ambrose Fleming.
Was constructed with 2 electrodes in the form of a
In 1906, Lee Dee Forest added a 3rd electrode called a
control grid and the triode, which is used as amplifier,
The application of triode created a new era in
broadcasting with the invention of the crystal radio sensor
by Pickard, 1912.
Commonly used in DC power supply units as a rectifiers
and voltage regulators, clipper, clamper circuit.
Comes in different shape and sizes
Made from a combination of 2 extrinsic semiconductors, P-type ad
The joint between the P-type and N-type material is called PN
Have 2 terminal( anode and cathode).
Produced from the silicon wafer
Near the PN junction the electrons diffuse into the vacant holes in the P material causing a
depletion zone.This depletion zone acts like an insulator preventing other free electrons in the
N-type silicon and holes in the P-type silicon from combining.
In addition this leaves a small electrical imbalance inside the crystal. Since the N region is
missing some electrons it has obtained a positive charge. And the extra electrons that filled the
holes in the P region, have given it a negative charge. Unfortunately one cannot generate
power from this electrical imbalance. However the stage is set to see how the PN junction
functions as a diode.
At the p-n junction, electrons from the n-type
semiconductor will be attracted to the holes in the p-type
As a result, the holes and the electrons at the p-n
junction disappear, forming a layer called “depletion
At the same time, the p-type semiconductor becomes
more negative whereas the n-type semiconductor
becomes more positive.
This will result a potential difference across the p-n
junction. This potential difference is called the junction
voltage (or the barrier voltage).
The junction voltage will prevent the charge carrier from
flowing across the depletion layer.
The polarity of applied voltage which causes
charge to flow through the diode is
called Forward Bias. (all current, almost no
The polarity of applied voltage which can't
produce any current is called Reverse Bias.(all
volts, almost no current)
Forward region: It is the operation region at which the
potential applied to anode is more positive than that
applied to the cathode.
Reverse Region: It is the operation region at which anode
potential is more negative than cathode potential.
Saturation Region: Part of the reverse region where the
diode impedance is very high, and causes very small drift
Break Down Region:The part of the reverse region
where the diode impedance is very low, and the
current passing through the diode is very high.
ThresholdVoltageVT: It is also called the knee
region. It can be determined on the I-V curve by
the point at which diode starts to conduct current
easily. It is also called the diode
barrier potential and is very near in amplitude to
the diode build-in voltage.
Saturation Current: it is a very small current due to
drift current in the diode in the reverse bias region.
This current is very low (in the nano-amperes range)
due to the high impedance of the depletion region.
Break DownVoltage: It is the maximum allowable
voltage in the reverse bias region, at which diode
resistance changed abruptly from very high
impedance to very low impedance. If the reverse
voltage applied on the diode exceeds this limit, a very
high current in the reverse direction passes through
the diode causing in burning it.
Circuit that converts the pulsating AC voltage to
a DC voltage.
The main function of filter is to reduce the ripple
in the input waveform.
Capacitor filter is very popular because of its low
cost, small size, light weight and good