Diode
Invented in 1904 by John Ambrose Fleming.
Was constructed with 2 electrodes in the form of a
vacuum tube.
 In 1906, Lee Dee Forest added a 3rd electrode called a
control grid and the triode, which is used as amplifier,
switch..
 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
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and voltage regulators, clipper, clamper circuit.
Comes in different shape and sizes

Made from a combination of 2 extrinsic semiconductors, P-type ad
N-type material.

The joint between the P-type and N-type material is called PN
junction.

Have 2 terminal( anode and cathode).

Produced from the silicon wafer
DEPLETION REGION
AND
JUNCTION VOLTAGE
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.
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At the p-n junction, electrons from the n-type
semiconductor will be attracted to the holes in the p-type
semiconductor.
As a result, the holes and the electrons at the p-n
junction disappear, forming a layer called “depletion
layer”.
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.
REVERSE BIAS
&
FORWARD BIAS

The polarity of applied voltage which causes
charge to flow through the diode is
called Forward Bias. (all current, almost no
volts)

The polarity of applied voltage which can't
produce any current is called Reverse Bias.(all
volts, almost no current)
I-V Characteristic Curve

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
current.

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.

Threshold Voltage VT: 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 Down Voltage: 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.
DIODES APPLICATION

Rectifying power supply circuit
(Rectifier = penerus)
• signal sensor in radar
• Voltage regulator in power supply circuit.
• Voltage clipper in power supply circuit
 Indicator light in electronic circuit
• Oscillator circuit in an oscilloscope
• Variable capacitor in a tune circuit
• Light sensor in a remote control unit
• Focused single colour light source
in compact disc player
DIODE APPLICATION
i.
DC Power Supply
ii.
Rectifier
iii.
Filter
iv.
Voltage regulator
DC POWER SUPPLY
RECTIFIER
2 types of rectifier
Half wave rectifier
Two diode full wave
rectifier
Full wave rectifier
Bridge diode full wave
rectifier
HALF WAVE RECTIFIER

Can produce ripple voltage during both positive
and negative input cycle.

There are 2 types of full wave rectifier:
I. Two diodes full wave rectifier
II. Bridge rectifier
TWO DIODES
FULL WAVE RECTIFIER
FULL WAVE
BRIDGE RECTIFIER
FILTER

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
characteristics
▪RC Filter

LC (T) Filter
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LC (𝝿
) Filter

RLC Filter
VOLTAGE
REGULATOR

Stabilize the output voltage.

Reduce the ripple at the output voltage of the
filter circuit.
IC
VOLTAGE
REGULATOR

Commonly use 78xx series.

Provides a constant positive output
voltage.
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The two final xx digits designate the
value of the output voltage.