Analog Electronics

ANALOG
ELECTRONICS
Unit 4
Zener Diode Explanation
A Zener Diode, also known as a breakdown diode, is a
heavily doped semiconductor device that is designed to
operate in the reverse direction. When the voltage across the
terminals of a Zener diode is reversed and the potential
reaches the Zener Voltage (knee voltage), the junction
breaks down and the current flows in the reverse direction.
This effect is known as the Zener Effect.
Zener Diode Specifications
Some commonly used specifications for Zener diodes are as follows:
•Zener/Breakdown Voltage – The Zener or the reverse breakdown voltage ranges
from 2.4 V to 200 V, sometimes it can go up to 1 kV while the maximum for the
surface-mounted device is 47 V.
•Current Iz (max) – It is the maximum current at the rated Zener Voltage (Vz –
200μA to 200 A)
•Current Iz (min) – It is the minimum value of current required for the diode to
breakdown.
•Power Rating – It denotes the maximum power the Zener diode can dissipate. It is
given by the product of the voltage of the diode and the current flowing through it.
•Temperature Stability – Diodes around 5 V have the best stability
•Voltage Tolerance – It is typically ±5%
•Zener Resistance (Rz) – It is the resistance to the Zener diode exhibits.
BIPOALAR JUNCTION TRANSISTOR
OPTOELECTRONICS
DEVICES
Optoelectronics is the communication between optics and
electronics which includes the study, design and
manufacture of a hardware device that converts electrical
energy into light and light into energy through
semiconductors. This device is made from solid crystalline
materials which are lighter than metals and heavier than
insulators. Optoelectronics device is basically an
electronic device involving light. This device can be found
in many optoelectronics applications like military
services, telecommunications, automatic access control
systems and medical equipment's.
Types of Optoelectronics Devices
Optoelectronics are classified into different types such as
•Photodiode
•Solar Cells
•Light Emitting Diodes
•Optical Fiber
•Laser Diodes
Photo Diode
A photo diode is a semiconductor light sensor that
generates a voltage or current when light falls on the
junction. It consists of an active P-N junction, which is
operated in reverse bias. When a photon with plenty of
energy strikes the semiconductor, an electron or hole pair
is created. The electrons diffuse to the junction to form an
electric field.
Solar Cells
A solar cell or photo-voltaic cell is an electronic device that
directly converts sun’s energy into electricity. When sunlight
falls on a solar cell, it produces both a current and a voltage to
produce electric power. Sunlight, which is composed of
photons, radiates from the sun. When photons hit the silicon
atoms of the solar cell, they transfer their energy to lose
electrons; and then, these high-energy electron flow to an
external circuit.
Light-Emitting Diodes
Light-emitting diode is a P-N semiconductor diode in which the
recombination of electrons and holes yields a photon. When the
diode is electrically biased in the forward direction, it emits
incoherent narrow spectrum light. When a voltage is applied to
the leads of the LED, the electrons recombine with the holes
within the device and release energy in the form of photons.
This effect is called as electroluminescence. It is the conversion
of electrical energy into light. The color of the light is decided
by the energy band gap of the material.
Optical Fiber
An optical fiber or optic fibre is a plastic and transparent fiber made of plastic
or glass. It is somewhat thicker than a human hair. It can function as a light
pipe or waveguide to transmit light between the two ends of the fiber. Optical
fibers usually include three concentric layers: a core, a cladding and a jacket.
The core, a light transmitting region of the fiber, is the central section of the
fiber, which is made of silica. Cladding, the protective layer around the core, is
made of silica.This creates an optical waveguide that limits the light in the core
by total reflection at the interface of the core-cladding. Jacket, the non-optical
layer around the cladding, typically consists of one or more layers of a polymer
that protect the silica from the physical or environmental damage.
Laser Diodes
Laser (light amplification by stimulated emission of radiation)
is a source of highly monochromatic, coherent and directional
light. It operates under stimulated emission condition. The
function of a laser diode is to convert electrical energy into light
energy like infrared diodes or LEDs. The beam of a typical laser
has 4×0.6mm extending at a distance of 15 meters. The most
common lasers used are injection lasers or semiconductor
lasers. The semiconductor laser changes from other lasers like
solid, liquid and gas lasers
COMPARATOR
A comparator is an electronic circuit, which
compares the two inputs that are applied to it and
produces an output. The output value of the
comparator indicates which of the inputs is greater or
lesser. An op-amp consists of two input terminals and
hence an op-amp based comparator compares the two
inputs that are applied to it and produces the result of
comparison as the output. This chapter discusses
about op-amp based comparators.
Types of Comparators
Comparators are of two types : Inverting and Non-inverting.
This section discusses about these two types in detail.
Inverting Comparator:
An inverting comparator is an op-amp based comparator for
which a reference voltage is applied to its non-inverting
terminal and the input voltage is applied to its inverting
terminal. This comparator is called as inverting comparator
because the input voltage, which has to be compared is
applied to the inverting terminal of op-amp.
Non-Inverting Comparator:
A non-inverting comparator is an op-amp based comparator
for which a reference voltage is applied to its inverting
terminal and the input voltage is applied to its non-inverting
terminal. This op-amp based comparator is called as non-
inverting comparator because the input voltage, which has to
be compared is applied to the non-inverting terminal of the
op-amp.

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