UNIT-5

BASIC ELECTRONIC CIRCUITS AND INSTRUMENTATION

Power supply:
A power supply is a component that supplies power to at least one electric load. Typically, it converts
one type of electrical power to another, but it may also convert a a different form of energy – such as
solar, mechanical, or chemical – into electrical energy.
A power supply provides components with electric power. The term usually pertains
to devices integrated within the component being powered. For example, computer power supplies
convert AC current to DC current and are generally located at the rear of the computer case, along
with at least one fan.
A power supply is also known as a power supply unit, power brick or power adapter.

Block diagram of DC power supply:

A regulated power supply can convert unregulated an AC (alternating current or voltage) to a constant
DC (direct current or voltage). A regulated power supply is used to ensure that the output remains
constant even if the input changes. A regulated DC power supply is also called as a linear power
supply, it is an embedded circuit and consists of various blocks.
The regulated power supply will accept an AC input and give a constant DC output. Figure below
shows the block diagram of a typical regulated DC power supply

The basic building blocks of a regulated DC power supply are as follows:

1. A step down transformer
2. A rectifier
3. A DC filter
4. A regulator
Step Down Transformer
The transformer that has a larger number of turns in the primary winding and a smaller number for the
secondary winding is called a step-down transformer.
So as we can see from the previous equation for the relation between the number of turns in winding
and voltage if the number of turns in the primary is greater than the number of turns in the secondary,
then the EMF generated in the secondary is less than the primary input.
Hence, we get a lower voltage in the secondary coil of a step-down voltage transformer.
As the name indicates, the step-down transformer is used for converting higher voltage power into
lower voltage power.

Rectification
Rectifier is an electronic circuit consisting of diodes which carries out the rectification process.
Rectification is the process of converting an alternating voltage or current into corresponding direct
(DC) quantity. The input to a rectifier is ac whereas its output is unidirectional pulsating DC. Usually
a full wave rectifier or a bridge rectifier is used to rectify both the half cycles of the ac supply (full
wave rectification). Figure below shows a full wave bridge rectifier.'
DC Filtration'
The rectified voltage from the rectifier is a pulsating DC voltage having very high ripple content. But
this is not we want, we want a pure ripple free DC
Filter are one or more electrolytic capacitors in parallel that flattens or smooths the previous wave
eliminating the alternating current (AC) component delivered by the rectifier.
These capacitors are charged to the maximum voltage value that the rectifier can deliver, and they are
discharged when the pulsating signal disappears.

Regulation
This is the last block in a regulated DC power supply. The output voltage or current will change or
fluctuate when there is change in the input from ac mains or due to change in load current at the
output of the regulated power supply or due to other factors like temperature changes. This problem
can be eliminated by using a regulator. A regulator will maintain the output constant even when
changes at the input or any other changes occur. Transistor series regulator, Fixed and variable IC
regulators or a zener diode operated in the zener region can be used depending on their applications.
IC’s like 78XX and 79XX are used to obtained fixed values of voltages at the output. waveform.
Hence a filter is used. Different types of filters are used such as capacitor filter, LC filter, Choke input
filter, π type filter.

Rectifier:
A rectifier is an electronic device that converts an alternating current into a direct current by using one
or more P-N junction diodes. A diode behaves as a one-way valve that allows current to flow in a
single direction. This process is known as rectification.

A rectifier can take the shape of several physical forms such as solid-state diodes, vacuum tube
diodes, mercury-arc valves, silicon-controlled rectifiers, and various other silicon-based
semiconductors switches.
Different Types of Rectifier

Rectifiers are mainly classified into two types as:

1. Uncontrolled Rectifier
2. Controlled Rectifier

Uncontrolled Rectifiers

The type of rectifier whose voltage cannot be controlled is known as an uncontrolled rectifier.
Uncontrolled rectifiers are further divided as follows:

 Half Wave Rectifier

 Full Wave Rectifier
The type of rectifier that converts only the half cycle of the alternating current into the direct current
is known as a half-wave rectifier. Likewise, a full-wave rectifier converts both positive and negative
half cycles of the AC. An example of this is a bridge rectifier. A bridge rectifier uses 4 diodes that are
connected in the form of a Wheatstone bridge.

Controlled Rectifiers

A type of rectifier whose voltage can be varied is known as the controlled rectifier. We use SCRs,
MOSFETs and IGBTs to make an uncontrolled rectifier a controlled one. These rectifiers are
preferred over their uncontrolled counterparts. There are two types of controlled rectifiers, and they
are Half Wave Controlled Rectifier and Full Wave Controlled Rectifier. Half-wave controlled rectifier
has the same design as the half-wave uncontrolled rectifier except we replace the diode with an SCR.

Full Wave Rectifier :

A full wave rectifier is defined as a rectifier that converts the complete cycle of alternating current
into pulsating DC.

Unlike halfwave rectifiers that utilize only the halfwave of the input AC cycle, full wave rectifiers
utilize the full cycle. The lower efficiency of the half wave rectifier can be overcome by the full wave
rectifier.

Full Wave Rectifier Circuit

The circuit of the full wave rectifier can be constructed in two ways. The first method uses a centre
tapped transformer and two diodes. This arrangement is known as a centre tapped full wave rectifier.
The second method uses a standard transformer with four diodes arranged as a bridge. This is known
as a bridge rectifier. In the next section, we will restrict the discussion to the centre tapped full wave
rectifier only. You can read our article on bridge rectifier to learn the construction and working of
bridge rectifier in detail.

The circuit of the full wave rectifier consists of a step-down transformer and two diodes that are
connected and centre tapped. The output voltage is obtained across the connected load resistor.

Working of Full Wave Rectifier:-

The input AC supplied to the full wave rectifier is very high. The step-down transformer in the
rectifier circuit converts the high voltage AC into low voltage AC. The anode of the centre tapped
diodes is connected to the transformer’s secondary winding and connected to the load resistor. During
the positive half cycle of the alternating current, the top half of the secondary winding becomes
positive while the second half of the secondary winding becomes negative.

During the positive half cycle, diode D 1 is forward biased as it is connected to the top of the
secondary winding while diode D2 is reverse biased as it is connected to the bottom of the secondary
winding. Due to this, diode D1 will conduct acting as a short circuit and D2 will not conduct acting as
an open circuit

During the negative half cycle, the diode D1 is reverse biased and the diode D 2 is forward biased
because the top half of the secondary circuit becomes negative and the bottom half of the circuit
becomes positive. Thus in a full wave rectifiers, DC voltage is obtained for both positive and negative
half cycle.
Advantages of Full Wave Rectifier

 The rectification efficiency of full wave rectifiers is double that of half wave rectifiers. The
efficiency of half wave rectifiers is 40.6% while the rectification efficiency of full wave
rectifiers is 81.2%.
 The ripple factor in full wave rectifiers is low hence a simple filter is required. The value of
ripple factor in full wave rectifier is 0.482 while in half wave rectifier it is about 1.21.
 The output voltage and the output power obtained in full wave rectifiers are higher than that
obtained using half wave rectifiers.

The only disadvantage of the full wave rectifier is that they need more circuit elements than the half
wave rectifier which makes, making it costlier.

FULL WAVE RECTIFIER WITH CAPACITOR FILTER :

Even though the full wave rectifier rectify both positive and negative half cycles, the DC signal
obtained at the output still contains some ripples. To reduce these ripples at the output, we use a filter.

The filter is an electronic device that converts the pulsating Direct Current into pure Direct Current.

The filter is made up of a combination of electronic components such as resistors, capacitors, and
inductors. The property of inductor is that it allows the DC components and blocks the AC
components. The property of a capacitor is that it allows the AC components and blocks the DC
components.

In this tutorial, a center tapped full wave rectifier with a filter made up of capacitor and resistor is
explained. The filter made up of capacitor and resistor is known as capacitor filter.

In the circuit diagram, the capacitor C is placed across the load resistor R L.
The main duty of the capacitor filter is to short the ripples to the ground and blocks the pure DC (DC
components), so that it flows through the alternate path and reaches output load resistor RL.

During the positive half cycle, the diode (D1) current reaches the filter and charges the capacitor.
However, the charging of the capacitor happens only when the applied AC voltage is greater than the
capacitor voltage.

Initially, the capacitor is uncharged. That means no voltage exists between the plates of the capacitor.
So when the voltage is turned on, the charging of the capacitor happens immediately.

During this conduction period, the capacitor charges to the maximum value of the input supply
voltage. The capacitor stores a maximum charge exactly at the quarter positive half cycle in the
waveform. At this point, the supply voltage is equal to the capacitor voltage.

When the AC voltage starts decreasing and becomes less than the capacitor voltage, then the capacitor
starts slowly discharging.

The discharging of the capacitor is very slow as compared to the charging of the capacitor. So the
capacitor does not get enough time to completely discharged. Before the complete discharge of the
capacitor happens, the charging again takes place. So only half or more than half of the capacitor
charge get discharged.

When the input AC supply voltage reaches the negative half cycle, the diode D 1 is reverse biased
(blocks electric current) whereas the diode D2 is forward biased (allows electric current).

During the negative half cycle, the diode (D2) current reaches the filter and charges the capacitor.
However, the charging of the capacitor happens only when the applied AC voltage is greater than the
capacitor voltage.

The capacitor is not completely uncharged, so the charging of the capacitor does not happens
immediately. When the supply voltage becomes greater than the capacitor voltage, the capacitor again
starts charging.
In both positive and negative half cycles, the current flows in the same direction across the load
resistor RL. So we get either complete positive half cycles or negative half cycles. In our case, they are
complete positive half cycles.

How exactly the capacitor filter removes the ripples in the signal

The pulsating Direct Current (DC) produced by the full wave rectifier contains both AC and DC
components.

We know that the capacitor allows the AC components and blocks the DC components of the current.
When the DC current that contains both DC components and AC components reaches the filter, the
DC components experience a high resistance from the capacitor whereas the AC components
experience a low resistance from the capacitor.

Electric current always prefers to flow through a low resistance path. So the AC components will flow
through the capacitor whereas the DC components are blocked by the capacitor. Therefore, they find
an alternate path and reach the output load resistor R L. The flow of AC components through the
capacitor is nothing but the charging of a capacitor.

Amplifiers :
An amplifier is an electronic device that increases the voltage, current, or power of a signal.
Amplifiers are used in wireless communications and broadcasting, and in audio equipment of all
kinds. They can be categorized as either weak-signal amplifiers or power amplifiers.
Types of amplifiers:-
Weak-signal amplifiers : are used primarily in wireless receivers. They are also employed in
acoustic pickups, audio tape players, and compact disc players. A weak-signal amplifier is designed to
deal with exceedingly small input signals, in some cases measuring only a few nanovolts (units of 10 -
9
volt). Such amplifiers must generate minimal internal noise while increasing the signal voltage by a
large factor. The most effective device for this application is the field-effect transistor. The
specification that denotes the effectiveness of a weak-signal amplifier is sensitivity, defined as the
number of microvolts (units of 10-6 volt) of signal input that produce a certain ratio of signal output to
noise output (usually 10 to 1).
Power amplifiers : are used in wireless transmitters, broadcast transmitters, and hi-fi audio
equipment. The most frequently-used device for power amplification is the bipolar transistor.
However, vacuum tubes, once considered obsolete, are becoming increasingly popular, especially
among musicians.

Public Address System:-

This Public Address System increases the apparent volume of vocals, musical instruments, other
sound sources, or recorded sounds or music. The sound enhancement system can be used in public
places where announcers, performers, etc. and need to hear in a remote or large area. Typical
applications include sports fields, public transport and facilities, live or recorded music venues and
events. A PA system may include multiple microphones or other sources, a mixer to combine and
change multiple sources, and multiple amplifiers and speakers for higher volume or wider
distribution.

Basic Block Diagram of Public Address System

Here, you can see the public address system block diagram and its important blocks.

Components of a PA System

There are so many devices or components are used in PA system that depends upon their applications
and other factors. But the main three components of any public address system are explained below.
1. Microphone

The microphone is a very important part or component of a PA system. The microphone basically is a
transducer that converts acoustic energy or sound energy into electrical energy. It continuously
generates the pulsating electrical voltage according to the frequency of the sound energy applied to it.
Various types of microphones are used in the PA system. The main basic two types of microphones
are,
1. Handheld Microphone
2. Lapel Microphone
Other different types of microphones are,
 Wired Microphone
 Wireless Microphone
A wired microphone can be connected by a wire to the mixer or amplifier. It is very simple. But the
wireless microphone needs a battery and the frequency of its signal is also a very important factor.
The wireless microphone cannot be connected directly to the mixer or amplifier. A receiver is
required that can receive the signals sent by the microphone. This receiver is to be connected to the
amplifier.

2. Amplifier

The amplifier is the second part of a PA system. The main function of the amplifier is to amplify or
increase the volume level of the audio signal that can drive a loudspeaker. The requirement or size of
the amplifier depends upon the number and size of the loudspeaker. If the size of the loudspeaker is
very large or so many loudspeakers are to be connected then a very powerful amplifier is required.
The output of the amplifier is measured in watts or kilowatts.

3. LoudSpeaker

Loudspeakers play a very important role in the PA system. It converts electrical energy into acoustic
energy or sound energy. The loudspeakers are generally connected to the amplifier and it generates
sound according to the audio signal provided by the amplifier. There are different types of
loudspeakers are available according to their operating frequency.
1. Woofer - it operates at the lowest frequency audio signal such as Bass
2. Subwoofer - it also operates with low frequency but more than the woofer such as
bass and deep vocals
3. Squawker - it operates with medium-frequency audio signals such as vocals
4. Tweeter - it operates with high-frequency audio signals such as tone

4. Mixer

A mixer is not a necessary part of a PA system. But if there are multiple audio sources or multiple
microphones used in the PA system then a mixer is must required. The mixer is an electronic device
that can control multiple sound sources simultaneously. It can mix all the sound sources together and
play with a single loudspeaker with the help of an amplifier. So the mixer is generally connected
before the amplifier. Nowadays, there are so many amplifiers are available in the market that already
have an inbuilt mixer. So there is no need for an external additional mixer. All the microphones or
sound sources can be connected directly to the amplifier.
COMMON EMITTER AMPLIFIER ( RC COUPLED) : COMMON EMITTER
(RC COUPLED) amplifier is a basic type of amplifier with the various stages present in it. In other
words, if we describe COMMON EMITTER (RC COUPLED) amplifier we can say that an amplifier
that consists of resistors and capacitors which acts a voltage divides and couplers to form
multiple/single stage for better amplification. These are the basic circuits that are present in the
various types of electronic equipment especially in RF signal or other communication devices as it
helps in improving the signal strength through amplification.
What is an RC COUPLED Amplifier?
An amplifier with the multiple stages based on the necessary levels of amplification can be defined as
an RC COUPLED amplifier. It can be connected in any transistor configurations based on the
efficiency of the system. It is widely used in audio and video communication devices.
COMMON EMITTER (RC COUPLED) Amplifier Circuit Diagram
The COMMON EMITTER (RC COUPLED) Amplifier circuit may consists of various types of
transistor configurations connected with the resistors and the capacitors. The configurations can be of
the common emitter. Now we are discussing a single stage and two stages COMMON EMITTER
(RC COUPLED) amplifiers.
Single Stage (COMMON EMITTER (RC COUPLED) Amplifier
Single-stage COMMON EMITTER (RC COUPLED) amplifier can be termed as a preamplification
circuit. Because these circuits are designed to improve the strength of the weak signals for the further
amplification process.

Single Stage (COMMON EMITTER (RC COUPLED) Amplifier

Working:
This type of amplifier in the single-stage
consists of the resistors R1, R2 and the
capacitor. Here the capacitor is utilized so
that it can provide the smoothing effect to
the signal. It is capable of preventing the
DC signals to enter and allow the AC
one’s. The resistors R1 and the R2 that is
connected at the input side to see to that
the proper biasing voltage reaches the
transistor so that the amplification process
starts.
Further, the resistors that are present at the
emitter and the collector are responsible to
maintain the voltage drop to a minimum of up to 50 percent. With the help of the capacitors that are
present at the emitter and the collector to avoid negative feedback because the stability is a major
concern. In this way, the single-stage amplifier acts as the pre-amplifier.
Two-Stage COMMON EMITTER (RC COUPLED) Amplifiers
When the gain in the circuit is the major concern in such cases multiple stages for the amplifiers are
designed. The purpose of this design is that it can improve performance by increasing the factor of
gain in the circuit.

Two stage COMMON EMITTER (RC COUPLED) Amplifier

After the processing of the signal in the first stage the output of the first stage, the amplifier is
connected to the second stage as the input. This made possible with the coupling capacitor present at
the output of the first stage of the amplifier. One can observe after processing occurs at the second
stage the output signal obtained has the increased gain factor in it and it is in phase with the input
signal. In this way, the two stages COMMON EMITTER (RC COUPLED) amplifier works.

Frequency Response of COMMON EMITTER (RC COUPLED) Amplifier

Bandwidth can be considered to be the major factor
during the amplification of the signals. This can even
influence the gain factor. When the curve or the graph
is plotted in between the values of the gain and the
frequency of the amplifier the resultant curve obtained
is known as the frequency response of that particular
amplifier. The bandwidth is the difference between the
high and low frequency in which the gain remains at
its higher value. It could be seen in graph that at a
lower frequency the gain is low because the reactance
of the capacitor is low at lower frequency and
similarly at higher frequency the capacitor CE acts a
short cirucuit an so again the gain is low.
Frequency response of CE amplifier (RC coupled )
Electronic Instrumentation:-
Electronic Instrumentation is about the design, realisation and use of electronic systems for the
measurement of electrical and non-electrical quantities. Strongly related fields are measurement
science and data acquisition. Each of these disciplines has a specific function in solving a
measurement problem. The activity that is the basis of electronic instrumentation is measuring.

Block diagram of instrumentation system :

It is branch of engineering which deals with various types of instrument to record, monitor, indicate
and control various physical parameters such as pressure, temperature, etc.

Block diagram of instrumentation system

The block diagram shown above is of basic instrumentation system. It consist of primary sensing
element, variable manipulation element, data transmission element and data presentation element.

Primary sensing element

The primary sensing element is also known as sensor. Basically transducers are used as a primary
sensing element. Here, the physical quantity (such as temperature, pressure etc.) are sensed and then
converted into analogues signal.

Variable conversion element

It converts the output of primary sensing element into suitable form without changing information.
Basically these are secondary transducers.
Variable manipulation element
The output of transducer may be electrical signal i.e. voltage, current or other electrical parameter.
Here, manipulation means change in numerical value of signal. This element is used to convert the
signal into suitable range.
Data transmission element
Sometimes it is not possible to give direct read out of the quality at a particular place (Example –
Measurement of temperature in the furnace). In such a case, the data should transfer from one place to
another place through channel which is known as data transmission element. Typically transmission
path are pneumatic pipe, electrical cable and radio links. When radio link is used, the electronic
instrumentation system is called as telemetry system.
Data presentation or controlling element
Finally the output is recorded or given to the controller to perform action. It performs different
functions like indicating, recording or controlling.