ACTIVE ELEMENTS:
What are active
elements?
An
active element is a component or a device in a circuit that is capable of
generating or producing energy. In reality, energy is stored in the active
elements in non-electrical form that is then converted into electrical form.
Active elements can be categorized into current and voltage sources as both
provide a drive to the circuit and manage the flow in it. Voltage sources are
those sources due to which the voltage at the terminal is equal to the voltage
present internally. On the other hand,current sources keep the terminal current
same to that of the internal current. Thus voltage sources have series
impedances which are relatively same, while current sources would have shunt
admittances almost equals to zero.
In an
ideal voltage source the current from the source varies depending upon the loadconnected.
Likewise in an ideal current source, the voltage across the source varies
depending on the circuit parameters. However, it is not possible practically to
construct an ideal source.
Sources
can be classified into two types: mainly independent sources and the dependent sources.
In independent sources, the generated voltage or current does not rely on any other
circuit voltage or current and the value is constant being unaffected. Whereas,
dependent sources have the voltage that depends on any other circuit current or
voltage.
INDEPENDENT
SOURCES:
Independent sources are those that generate
electrical energy. The output voltage of an independent voltage or current
source does not depend on any circuit element i.e. whatever load or passive
element is attached, its value of energy dissipation wills not alter.an ideal
voltage source has zero internal resistance and can never be short circuited.
Internal ideal current source has infinite internal
resistance due to which maximum voltage drop is there and all of the current
flows out into the circuit. It can never be open circuited.
THE ABOVE TWO MENTIONED GRAPHS SHOWS HOW A PRACTICAL
INDEPENDENT CURRENT AND VOLTAGE SOURCE DIFFERS FROM THE IDEAL ONE.
DEPENDENT SOURCES:
Dependent sources, also
referred to as controlled sources, do supply energy to the circuit but they
rely on any other factor, either current or voltage, of source for their
functionality.
There are four further categories of how these
dependent sources rely on other independent source of the circuit or even any
varying quantity such as current or voltage across a branch. These are usually
representated b y a diamond shaped source that shows that it is dependent.
These descriptions are
described as:
·
VOLTAGE
CONTROLLED VOLTAGE SOURCE
·
VOLTAGE
CONTROLLED CURRENT SOURCE
·
CURRENT
CONTROLLED CURRENT SOURCE
·
CURRENT CONTROLLED
VOLTAGE SOURCE
VOLTAGE CONTROLLED VOLTAGE SOURCE (VCVS)
A voltage controlled
voltage source has its output a factor times to the voltage at any other point
on the circuit.
Vs=αVx
Where α is a constant
and Vx is the voltage across any given element.
VOLTAGE
CONTROLLED CURRENT SOURCE (VCCS)
A voltage controlled
current source has its output a factor times to the voltage at any other point
on the circuit. The output is current
Is=βvx
Where β is a constant
and Vx is the voltage across any given element.
CURRENT CONTROLLED CURRENT SOURCE (CCCS)
A current controlled
current source gives an output that depends upon the current flowing through any part of the
circuit. The output current is
Is=γIx
Where γ is a constant and Ix is the current
across any given element.
CURRENT CONTROLLED
VOLTAGE SOURCE:
A current controlled voltage source gives an output that depends
upon the current across any part of the circuit. The output voltage is
Vs=μIx
Where μ is a constant
and Ix is the current flowing in the circuit taken into consideration.
There are a number of active elements that are both independent
and dependent and so they contribute to the contribute to the circuit by
providing a flow into it.
Some of them are mentioned below:
Ø Power supply
o A.c
o D.c
o Batteries
Ø Generators
Ø Transformers
Ø Transistors
Ø Operational amplifier
And many more.
This report gives a brief description of how
these elements function thus completing the circuit.
POWER SUPPLY:
A power supply is a device that supplies electric power to an
electric load. It controls the output voltage or current to a specific value;
the controlled value is held nearly constant despite variations in either load
current or voltage supplied by power supply’s energy source.
Common examples of this
include
·
Power supplies that
convert ac line voltage to dc voltage.
·
Energy storage devices
such as batteries and fuel cells.
·
Electromechanical
systems such as generators and alternators.
·
Solar power.
AC POWER SUPPLY
An
ac power supply typically takes the voltage from the main supply and makes it
to the desired voltage. It is actually the sinusoidal wave form that comes as
an input to the circuit.
DC POWER SUPPLY:
It
a straight line wave form that is constant and is rectified form of the A.c
supply. Batteries give D.c supply. Mobile phones operate on dc supply.
BATTERY:
A
battery is a device that converts stored chemical energy to electrical energy. USES:
Energy
sources in many household
Industrial
applications.
There
are two types of batteries: primary batteries (disposable batteries), which are
designed to be used once and discarded, and secondary batteries (rechargeable
batteries), which are designed to be recharged and used multiple times.
Batteries come in many sizes, from miniature
cells used in hearing aids and wristwatches to room-size battery banks that
serve as backup power supplies in telephone exchanges and computer data
centers.
GENERATORS:
Electric generator works
over the principle of converting mechanical energy, provided by the external
system, into electrical energy by the principle of magnetic induction.
They provide power that runs machines in factories, provides lighting, and
operates homeappliances.
The size of large generators is usually measured in kilowatts. One kilowatt equals 1,000 watts.
There are two main types of generators.
The size of large generators is usually measured in kilowatts. One kilowatt equals 1,000 watts.
There are two main types of generators.
Direct-current (DC)
generators produce electric current that always flows in the same direction.
Alternating-current (AC) generators, or alternators, produce
electric current that reverses direction many times every second.
Both kinds of generators work on the same scientific principles.
But they differ in the ways they are built and used.
TRANSFORMERS:
Transformers
works over the principle of magnetic induction.there are two types of winding
namely primary and secondary. When a current is supplied to the primary winding
a magnetic flux is generated in the coil and by the law of magnetic induction
and continuous change in magnetic flux, a voltage is induced at the secondary
coil which is used as the output.
The
number of turns of the coil usually contributes by increasing or decreasing the
output voltage. This is known as:
·
Step up transformer:
where voltage is increased at the output terminal.
·
Step down transformer:
that reduces the voltage at the output terminal.
TRANSISTORS:
According to a website following description of transistor and its
working is shown.
Transistors are semiconductors found everywhere in electronic
circuits. They are used as amplifiers and switching devices. As amplifiers,
they are used in high and low frequency stages, oscillators, modulators,
detectors and in any circuit needing to perform a function. In digital circuits
they are used as switches.
Being forward or reverse biased, a transistor allows current to
pass through or even opposes it depending upon its placement. Moreover, it
depends upon the base current flowing.
Some types of transistors are:
·
Bipolar junction
transistor
·
Field- effect transistor
·
Diffusion transistor
·
Unijunction transistor,
etc
OPERATIONAL AMPLIFIER
(op-amp):
An operational amplifier is
a device used to compare between two voltages being input into it and amplify it.
It
is used as
·
A comparator
It compares the two voltages that can be
monitored in terms of temperature change or light dependency as well. It
involves the usage of negative feedback where one output is used as an input
next time.
·
It uses negative feedback but not all of the
output voltage is fed back into the inverting input (-)
·
Non inverting amplifier
Here the input voltage is applied to the
non-inverting input; part of the output voltage is fed back to the inverting
input.
Thus, by op-amp usage the gain is increased
to a higher value but it is made sure that the overall gain is almost the same
due to which distortion is less and the signal remain constant for large
frequencies as well.
GÆ¡=output
voltage/input voltage
An ideal op-amp has the following
characteristics:
1. Infinite open loop gain
voltage(no feedback used)
2. Infinite input
resistance(no current drawn from supply)
3. Zero output resistance(no
internal resistance no voltage drop)
4. Infinite bandwidth(same
over large frequencies)
5. Infinite slew rate( time
delay between input and output)
6. Zero noise contribution
