ME 3024 FUNDAMENTALS OF ELECTRICAL ENGINEERING

MODULE 4
CO3
M4.01 Distinguish various active and passive electronic 4 Understanding
components.
M4.02 Describe the working of various diode rectifiers. 4 Understanding
M4.03 Illustrate the working of BJT and SCR based circuits 4 Understanding
M4.04 Identify the elements of electric drives. 2 Understanding
Contents:
Electronic components- Active and Passive Components-Different types of resistors and
capacitors used in electronics. PN junction diode - working-rectifier circuits using diodes
Transistor- working – transistor as a switch. Power electronic components- SCR- working-
SCR based circuits- basic diagram and working-rectifier-chopper Introduction to electric
drives (block diagram approach only)- basic block diagram of EV charging system

ACTIVE & PASSIVE COMPONENTS

Active Components
An active component is an electronic component which supplies energy to a circuit.
Common examples of active components include:
• Voltage sources
• Current sources
• Generators (such as alternators and DC generators)
• All different types of transistors (such as bipolar junction transistors, MOSFETS, FETs, and
JFET)
• Diodes (such as Zener diodes, photodiodes, Schottky diodes, and LEDs)

Passive Components
A passive component is an electronic component which can only receive energy, which it can either
dissipate, absorb or store it in an electric field or a magnetic field. Passive elements do not need any form
of electrical power to operate.
As the name ‘passive’ suggests – passive devices do not provide gain or amplification. Passive
components cannot amplify, oscillate, or generate an electrical signal.
Common examples of passive components include:
 • Resistors
• Inductors
• Capacitor

Types of resistors
1. Wire wound resistors
The designing of this resistor can be done using a conductive wire by wounding around
a non-conductive core. Generally, the material of the wire can be made with like
Nichrome (Nickel-chromium alloy) or Manganin (copper-nickel-manganese
alloy). These resistors generate very accurately, excellent properties for high power
ratings & low resistance values.

The resistance of this resistor changes from 1ohm-1Mega Ohm as well as power
dissipation can change from 5- 250 watt. The range of tolerance may range from 5% to
-10 %. These resistors are applicable for high power applications. The resistance of this
resistor mainly depends on three factors like
• The resistivity of the metal wire,
 • Length of the metal wire
• The cross-sectional area of the metal wire
Advantages of Wire Wound Resistor
• This resistor is employed in high power circuits
• It will not affect by the noise
• It is thermally constant.
Disadvantages of Wire Wound Resistor
• These resistors are used for only low frequencies because it works as an inductor at
high frequencies
• Therefore, non-inductive type resistors are used for high frequencies.
• It is expensive as compared with carbon size resistor
• It is larger in size
2. Carbon composition Resistor
It uses a cylindrical shaped solid resistive element, which is formed by the blending of
carbon particles, graphite powder, and ceramic powder (made with clay). There are two
connecting leads or electrodes at both ends of the resistive element. These leads or
electrodes are also known as metal cap ends, and are made with copper. Since the
carbon mixture is mainly used in construction because it is the good conductor of
electricity. An insulating material like plastic is wrapped around the resistive element
to protect the carbon composition from the dust, heat, and other environmental
conditions. These are very cheap, smaller in size, safe for all types of circuits. The
resistance of the carbon composition resistor changes quickly. So, it has poor stability.
It produces high noise. The accuracy is low

3. Film type resistor

As the name indicates, the metal film resistor is made by depositing a thin layer of metal
onto a ceramic former. The metal film acts in the same way as resistance wire, and as
the thickness, width and length can be accurately controlled, the metal film resistor can
be produced to a high tolerance Typically film thicknesses between 50 and 250nm are
 used as material thicknesses in this region tend to provide a greater long term stability
level. The metal that is deposited is normally nickel chromium, NiCr, but other metals
including gold with platinum, or tantalum nitride may be used for specialised
applications.

Once the film has been deposited, a metal end cap is pressed over the deposited metal.
This makes contact with the resistive film and has the leads incorporated.

4. Variable Resistor
A variable resistor is a type of resistor whose electrical resistance value can be
adjusted on demand. Variable resistors are used in an electronic circuit to adjust circuit
resistance as a means to control the voltage or current within a circuit (as per Ohm’s
Law). The electrical resistance is varied by sliding a wiper contact along a resistance
track. It mainly consists of a resistance track and a wiper contact. The wiper contact
moves along the resistance track when the adjustable component is adjusted.

PN Junction diode
 By joining a P type semiconductor to an N type semiconductor, a PN junction is formed.
PN junction diode conducts current only in one direction and offers high resistance in the
other direction
Symbol of PN Junction diode

Fig. 4.1 symbol of PN junction diode

Under normal conditions, holes from P side diffuse into N side where they recombine with free
electrons. Free electrons diffuse from N side to P side and combine with holes. Each
recombination depletes holes and electrons near the junction and contains only immobile ions
and devoid of free carriers. This region is called depletion region. The electric field formed in
the depletion region creates a potential difference across the junction is called barrier potential
(0.7 V for Silicon and 0.3 V for germanium). The potential difference across the junction by
the electric field formed due to the depletion region is called potential barrier.

Fig. 4.2 Formation of depletion region

When no external energy source is applied, natural Potential Barrier is developed across the
junction. In order to overcome the barrier potential developed across the junction and to make
the diode function for the purpose it is designed for, external energy has to be applied. This
process is defined as biasing.
Forward Biasing
In forward basing Positive terminal of the battery is connected to the P-type material and
negative terminal of the battery is connected to the N-type material. Applied forward potential
establishes an electric field which acts against the field due to the potential barrier. Hence, the
resultant field is weakened and the depletion region is reduced.

Fig. 4.3 Forward biasing of a PN Junction

When the diode is forward biased, negative voltage repels the electrons from the N region and
they move towards the junction. The positive voltage repels holes from the P region and they
move towards the junction. At junction some electrons crosses the junction and combines with
holes. The net result is that the depletion layer becomes smaller and offers a low resistance
path. Since the potential barrier voltage is very small (0.3 to 0.7 V), a small forward voltage is
sufficient to completely eliminate the barrier. Once the potential barrier is eliminated, junction
resistance becomes almost zero and a low resistance path is established for the entire circuit.
Thereby forward current flows in the circuit.

Fig. 4.4 Forward characteristics

Reverse Biasing
In reverse biasing, negative terminal of the battery is connected to the P-type material
and positive terminal is connected to the N-type material. This applied reverse voltage
establishes an electric field which acts in the same direction as the field due to the potential
barrier. Hence, the resultant field at the junction is strengthened and the barrier height is
increased.
In reverse biasing, positive voltage applied to the N-type material attracts electrons
from the N region and they move away from the junction. The Negative voltage applied to
the P-type material attracts the holes from the P region and they move away from the junction.
The net result is that the depletion layer becomes wider and offers a high resistance path. The
increased potential barrier prevents the flow of charge carriers across the junction. Hence, a
high resistance path is established for the entire circuit and therefore no current flows.
However, in reverse biased p-n junction diode minority charge carriers carry the electric
current. This current is called reverse saturation current. If the applied reverse voltage is
increased to a large value, large current will flow through the diode and the junction
breakdown. This voltage is called reverse breakdown voltage

Fig. 4.5 Reverse Biased characteristics Fig.4.6 Diode characteristics

Rectifiers
A P-N junction diode allows electric current to flow in forward biased condition and blocks
the current in reverse biased condition. A diode thus allows electric current to flow only in one
direction. This property of diode allows it to function as a rectifier. A rectifier is thus an
electronic device that converts an alternating current into a direct current by using one or more
diodes. This process of converting AC to DC is known as rectification.
Based on the cycles of the input signal that the rectifier rectifies, we can classify rectiers into
two major types. They are
 • Half wave rectifier
• Full wave rectifiers
Full wave rectifiers are of two types. They are full wave centre tapped rectifiers and full wave
bridge rectifiers.

Fig. 4.7 Classification of rectifiers

Half Wave Rectifiers

Half wave rectifiers rectify only one half-cycle of the input alternating waveform. It requires
only one diode. The circuit diagram for the half wave rectifier is shown below.

Fig.4.8 Circuit of a half wave rectifier

Working
During positive half cycle Diode D is forward biased and hence it conducts and current flows
through the load resistor. The output voltage is same as the input voltage.
During negative half cycle Diode D is reverse biased and it does not conduct and no current
flows through the load resistor. Thus the output voltage is zero. The input output waveforms
are shown below.
 Fig. 4.9 Waveforms of a half wave rectifier

Full wave Rectifiers

A Rectifier circuit that rectifies both the positive and negative half cycles can be termed as a
full wave rectifier as it rectifies the complete cycle. Full wave rectifier can be implemented in
two ways. They are
Center-tapped Full wave rectifier
Bridge full wave rectifier
Centre tapped Full Wave Rectifier
In a centre tapped full wave rectifier the secondary of the transformer is tapped at the midpoint.
The circuit uses two diodes to rectify full cycle of alternating input waveform. The circuit
diagram for a centre tapped rectifier is shown below.

Fig. 4.10 Circuit diagram of full wave centre tapped rectifier

Working
During positive half cycle of the input signal A is positive w.r.t to E and hence Diode D1 is
forward biased and D2 is reverse biased. Hence the current flows through load in the direction
given by ABCDA.
During negative half cycle of the input signal E is positive w.r.t to A and hence Diode D2 is
forward biased while D1 is reverse biased. Hence the current flows through in the direction
indicated by EFCDE.
In the both half cycles current flows through the load in the same direction. Hence the output
across the load is DC. The waveforms are given below.

Fig. 4.11 Input output waveforms of centre tapped rectifier

Full Wave Bridge Rectifier

In a full bridge rectifier four diodes are connected in the form of a bridge to rectify
the input signal. The circuit diagram is shown in the figure below.

Fig. 4.12 Full wave bridge rectifier circuit diagram

Working
During positive half cycle of the input signal A is positive w.r.t. B. Hence diodes
D1 and D2 are forward biased while D3 and D4 are reverse biased. Hence the
path of current is ACEDFB as indicated below
 Fig. 4.13 Operation of bridge rectifier for positive half cycle of input

During negative half cycle of the input signal B is positive w.r.t. A. Hence diodes
D4 and D3 are forward biased while D1 and D2 are reverse biased. Hence the
path of current is BFEDCA as indicated below

Fig. 4.14 Operation of bridge rectifier for negative half cycle of input

The input output waveforms are given in Fig. 4.15

Fig. 4.15 Input output waveforms of bridge rectifier

ELECTRIC DRIVES
✓ An electric drive can be defined as an electromechanical device for converting electrical
energy into mechanical energy to impart motion to different machines and mechanisms
for various kinds of process control.
✓ An electric drive is an industrial system which performs the conversion of electrical
energy into mechanical energy or vice versa for running and controlling various
processes.
✓ An electric drive is defined as a form of machine equipment designed to convert
electrical energy into mechanical energy and provide electrical control of the processes.
The system employed for motion control is called an electrical drive.
BLOCK DIAGRAM OF ELECTRIC DRIVES
An electrical drive system has the following components
1. Electrical machines and loads
2. Motor
3. Power modulator
4. Sources
5. Control unit
6. Sensing unit

Power Converter:
Performs one or more of the following functions.
i. Converts Electrical energy from the source into a form suitable to the motor,
say AC to DC for a DC motor and DC to AC for an Induction motor.
ii. Controls the flow of power to the motor so as to get the Torque Speed
characteristics as required by the load.
iii. Selects the mode of operation of the Motor i.e. Motoring or Braking
The load:
Can be any one of the systems like pumps, machines etc to carry out a specific task. Usually,
the load requirements are specified in terms of its speed/torque demands. An electrical motor
having the torque speed characteristics compatible to that of the load has to be chosen

Control unit/Sensing unit:

The control unit controls the operation of the Power converter based on the Input command
and the feedback signal continuously obtained from a suitable point (In a closed loop operation)
at the load end so as to get the desired load performance. The sensor unit gets the feedback on
voltage and current also to operate the motor within its safe operating conditions.
Electrical Motors:
The most commonly used motors are DC motors – Shunt, Series, Compound etc., AC motors-
Suirrelcage & Slip ring induction motors, Special motors like Brushless DC motors, stepper
motors etc

Advantages of Electric Drives

✓ Cost is too low as compared to another system of the drive.
✓ The system is simpler and cleaner.
✓ The control is very easy and smooth.
✓ Flexible in the layout.
✓ Facility for remote control.
✓ Transmission of power from one place to other can be done with the help of cables
instead of long shafts, etc.
✓ Its maintenance cost is quite low.
✓ It can be started at any time without delay
ELECTRIC VEHICLE CHARGING BLOCK DIAGRAM

A charging station, is a piece of equipment that supplies electrical power for charging plug-in
electric vehicles There are two main types: AC charging stations and DC charging stations.
Batteries can only be charged with direct current (DC) electric power, while most electricity is
delivered from the power grid as alternating current (AC). For this reason, most electric
vehicles have a built-in AC-to-DC converter, commonly known as the "onboard charger". At
an AC charging station, AC power from the grid is supplied to this onboard charger, which
produces DC power to charge the battery. DC chargers facilitate higher power charging by
building the converter into the charging station instead of the vehicle to avoid size and weight
restrictions. Primarily, in the AC/DC converters there are a variety of options to choose ranging
from single phase to three phases. The station then supplies DC power to the vehicle directly,
bypassing the onboard converter. Most fully electric car models can accept both AC and DC
power. Additionally, the charging systems can communicate with the power grid using power
line communication devices to adjust the charging based on power grid conditions.

Welding Transformer

Construction of welding transformer:

1. Welding transformer is a step-down transformer.

2. It has a magnetic core with primary winding which is thin and has large number of turns on
one arm.
3. A secondary winding with less number of turns and high cross-sectional area on the other
arm.
4. Due to this type of windings in primary and secondary it behaves as step down transformer.
5. So we get less voltage and high current from the secondary winding output. This is
the construction of ac welding transformer.
6.A dc welding transformer also has same type of winding the only difference is that we
connect a rectifier(which converts ac to dc) at the secondary to get dc output.
7.We also connect a inductor or filter to smooth the dc current. This will be construction of
dc welding transformer. The diagrams are shown below.

Fig. DC welding transformer

 Fig. AC welding transformer

The winding which is connected to power supply is called primary winding and the winding to
which load is connected is called secondary winding.

Working of welding transformer:

1.As it is a step down transformer we have less voltage at secondary which is nearly 15 to 45
volts and has high current values which is nearly 200 A to 600 A it can also be higher than this
value.
2. For adjusting the voltage on secondary side there are tappings on secondary winding by this
we can get required amount of secondary current for welding.
3. These tappings are connected to several high current switches.
4. Now one end of secondary winding is connected to the welding electrode and the other end
is connected to the welding pieces as shown in fig 2.
5.When a high current flows a large amount of I2R heat is produced due to contact resistance
between welding pieces and electrode.
6.Because of this high heat the tip of electrode melts and fills the gap between the welding
pieces.
Volt – ampere characteristics of welding transformer:
Figure given below shows the volt – ampere characteristics of welding transformer.
TRANSISTORS
A transistor has three terminals, namely emitter (E), base (B) and collector (C). We have two
types of transistors, npn and pnp. The emitter is heavily doped and injects a large number of
majority carriers into the base. The collector is moderately doped and has larger width
compared to base and emitter. The width of base is small and is very lightly doped. The emitter
is always forward biased with respect to the base. In pnp transistors, majority carriers are holes
and in npn transistors, majority carriers are electrons.
The current conduction in bipolar transistor is because of both the types of charge carriers i.e., holes
and electrons. Hence it is called as Bipolar Junction Transistor and it is referred to as BJT.

TRANSISTOR CONSTRUCTION
A transistor has three regions known as emitter, base and collector
Emitter:
it is a region situated in one side of a transistor, which supplies charge carriers (ie., electrons
and holes) to the other two regions. Emitter is heavily doped region
Base:
It is the middle region that forms two P-N junction in the transistor. The base of the transistor
is thin as compared to the emitter and is a lightly doped region
Collector:
It is a region situated in the other side of a transistor (ie., side opposite to the emitter) which
collects the charge carriers. The collector of the transistor is always larger than the emitter and
base of a transistor. The doping level of the collector is intermediate between the heavy doping
of emitter and the light doping of the base
WORKING OF NPN TRANSISTOR
 The n-p-n transistor with base to emitter junction forward biased and collector base
junction reverse biased is as shown in figure.

 As the base to emitter junction is forward biased the majority carriers emitted by the n
type emitter i.e., electrons have a tendency to flow towards the base which constitutes
the emitter Current IE
 As the base is p-type there is chance of recombination of electrons emitted by the
emitter with the holes in the p-type base. But as the base is very thin and lightly doped
only few electrons emitted by the n-type emitter, less than 5% combines with the holes
in the p- type base, the remaining more than 95% electrons emitted by the n-type emitter
cross over into the collector region constitute the collector current, IC
  To maintain base neutrality base electrode provides equal number of electrons which
have combined with holes to provide base current, IB
 Thus applying KCL, IE = IB + IC

WORKING OF PNP TRANSISTOR

 As the base to emitter junction is forward biased the majority carriers emitted by the
type emitter i.e., holes have a tendency to flow towards the base which constitutes the
emitter current IE.

 As the base is n-type there is a chance of recombination of holes emitted by the emitter
with the electrons in the n-type base. But as the base is very thin and lightly doped only
few electrons less than 5% combine with the holes emitted by the p-type emitter, the
remaining 95% charge carriers cross over into the collector region to constitute the
collector current, IC

 Some of the holes flow out via base terminal constituting base current, IB

TRANSISTOR AS A SWITCH
The input and Base are grounded ( 0 V ) The input and Base are connected to VCC
Base-Emitter voltage VBE < 0.7v • Base-Emitter voltage VBE > 0.7v
Base-Emitter junction is reverse biased • Base-Emitter junction is forward biased
Base-Collector junction is reverse biased • Base-Collector junction is forward biased
Transistor is “fully-OFF” (Cut-off region) • Transistor is “fully-ON” ( saturation region )
No Collector current flows ( IC = 0 ) • Max Collector current flows ( IC = Vcc/RL )
VOUT = VCE = VCC = “1” • VCE = 0 ( ideal saturation )

•Transistor operates as an “open switch” • VOUT = VCE = “0”

 • Transistor operates as a “closed switch”

SILICON CONTROLLED RECTIFIER(SCR)

SCR is a three terminal and three junction semiconductor device acts as true electronic switch.
It is a unidirectional device. It converts AC to DC and controls the amount of power fed to the
load. It contains the features of a rectifier and transistor. SCR is widely used device in the
Thyristor family, so it is commonly called as Thyristor.
Symbol of SCR

CONSTRUCTION
SCR consists of four semiconductor layers forming a PNPN structure as shown in the Figure.
There are three junctions namely J1, J2, J3. SCR have three leads, they are anode (A), cathode
(K) and gate (G). The end P-layer acts as anode, the end N-layer acts as cathode and the P-
layer nearer to cathode acts as gate.
WORKING
Reverse blocking mode of SCR:

Reverse blocking mode of SCR

The thyristor is switched off if no voltage is applied at the Gate terminal. When SCR is reverse
biased the anode is connected to the negative end and Cathode is connected to the positive end,
the junctions J1 and J3 are reverse biased and J2 is forward biased.

It acts like the conventional diode in reverse biased condition. Only reverse saturation current
flows. Reverse breakdown happens like the diode, when it exceeds the safe voltage.

Forward blocking mode of SCR:

Forward blocking mode of SCR

When SCR is forward biased the anode is connected to the positive end and Cathode is
connected to the negative end, the junctions J1 and J3 are forward biased and J2 is reverse
biased. It acts like the conventional diode in forward biased condition. Here also no current
flows, only small saturation current flows.
Forward conduction mode of SCR:

Forward conduction mode of SCR

When the thyristor is forward biased and small voltage is applied at the gate terminal, the device
is ON. In the two transistors model when the gate voltage is applied the lower transistor
switches ON which in turn switches ON the upper transistor. This continues till the power
supply applied to gate and anode terminals is stopped. The current flow continues even when
the applied voltage at the gate terminal is stopped.

SCR Rectifier circuit

A Single Phase Half Wave Controlled Rectifier circuit consists of SCR / thyristor, an AC
voltage source and load. The load may be purely resistive, Inductive or a combination of
resistance and inductance. For simplicity, we will consider a resistive load. A simple circuit
diagram of Single Phase Half Wave Controlled Rectifier is shown in figure below.

The necessary condition for turn ON of SCR is that, it should be forward biased and gate signal
must be applied. In other words, an SCR will only get turned ON when it is forward biased and
fired or gated. Let us assume that thyristor T is fired at a firing angle of α. This means when wt
= α, gate signal will be applied and SCR will start conducting. Refer the figure
Thyristor T is forward biased for the positive half cycle of supply voltage. The load output
voltage is zero till SCR is fired. Once SCR is fired at an angle of α, SCR starts conducting. But
as soon as the supply voltage becomes zero at ωt = π, the load current will become zero and
after ωt = π, SCR is reversed biased. Thus thyristor T will turn off at ωt = π and will remain in
OFF condition

ELECTRIC DRIVES
✓ An electric drive can be defined as an electromechanical device for converting electrical
energy into mechanical energy to impart motion to different machines and mechanisms
for various kinds of process control.
 ✓ An electric drive is an industrial system which performs the conversion of electrical
energy into mechanical energy or vice versa for running and controlling various
processes.
✓ An electric drive is defined as a form of machine equipment designed to convert
electrical energy into mechanical energy and provide electrical control of the processes.
The system employed for motion control is called an electrical drive.
BLOCK DIAGRAM OF ELECTRIC DRIVES
An electrical drive system has the following components
1. Electrical machines and loads
2. Motor
3. Power modulator
4. Sources
5. Control unit
6. Sensing unit

Power Converter:
Performs one or more of the following functions.
iv. Converts Electrical energy from the source into a form suitable to the motor,
say AC to DC for a DC motor and DC to AC for an Induction motor.
v. Controls the flow of power to the motor so as to get the Torque Speed
characteristics as required by the load.
vi. Selects the mode of operation of the Motor i.e. Motoring or Braking
The load:
Can be any one of the systems like pumps, machines etc to carry out a specific task. Usually,
the load requirements are specified in terms of its speed/torque demands. An electrical motor
having the torque speed characteristics compatible to that of the load has to be chosen

Control unit/Sensing unit:

The control unit controls the operation of the Power converter based on the Input command
and the feedback signal continuously obtained from a suitable point (In a closed loop operation)
at the load end so as to get the desired load performance. The sensor unit gets the feedback on
voltage and current also to operate the motor within its safe operating conditions.
Electrical Motors:
The most commonly used motors are DC motors – Shunt, Series, Compound etc., AC motors-
Suirrelcage & Slip ring induction motors, Special motors like Brushless DC motors, stepper
motors etc

Advantages of Electric Drives

✓ Cost is too low as compared to another system of the drive.
✓ The system is simpler and cleaner.
✓ The control is very easy and smooth.
✓ Flexible in the layout.
✓ Facility for remote control.
✓ Transmission of power from one place to other can be done with the help of cables
instead of long shafts, etc.
✓ Its maintenance cost is quite low.
✓ It can be started at any time without delay
ELECTRIC VEHICLE CHARGING BLOCK DIAGRAM
A charging station, is a piece of equipment that supplies electrical power for charging plug-in
electric vehicles There are two main types: AC charging stations and DC charging stations.
Batteries can only be charged with direct current (DC) electric power, while most electricity is
delivered from the power grid as alternating current (AC). For this reason, most electric
vehicles have a built-in AC-to-DC converter, commonly known as the "onboard charger". At
an AC charging station, AC power from the grid is supplied to this onboard charger, which
produces DC power to charge the battery. DC chargers facilitate higher power charging by
building the converter into the charging station instead of the vehicle to avoid size and weight
restrictions. Primarily, in the AC/DC converters there are a variety of options to choose ranging
from single phase to three phases. The station then supplies DC power to the vehicle directly,
bypassing the onboard converter. Most fully electric car models can accept both AC and DC
power. Additionally, the charging systems can communicate with the power grid using power
line communication devices to adjust the charging based on power grid conditions.