Silicon Controlled Rectifier (SCR) is a unidirectional semiconductor device made of silicon.SCR is a three-terminal, four-layer semiconductor device consisting of alternate layers of p-type and n-type material.
BJT small signal model – Analysis of CE, CB, CC amplifiers- Gain and frequency response – MOSFET small signal model– Analysis of CS and Source follower – Gain and frequency response- High frequency analysis.
Silicon Controlled Rectifier (SCR) is a unidirectional semiconductor device made of silicon.SCR is a three-terminal, four-layer semiconductor device consisting of alternate layers of p-type and n-type material.
BJT small signal model – Analysis of CE, CB, CC amplifiers- Gain and frequency response – MOSFET small signal model– Analysis of CS and Source follower – Gain and frequency response- High frequency analysis.
This article discusses different power electronics devices that are in use like power diodes, power thyristors, power transistors, IGBT, GTO, IGCT and others. This article will give a basic view of these devices and their operations.
The AC and DC bridge both are used for measuring the unknown parameter of the circuit. The AC bridge measures the unknown impedance of the circuit. The DC bridge measures the unknown resistance of the circuit.
The complete list of thyristor family members include diac (bidirectional diode thyristor), triac (bidirectional triode thyristor), SCR (silicon controlled rectifier), Shockley diode, SCS (silicon controlled switch), SBS (silicon bilateral switch), SUS (silicon unilateral switch) also known as complementary SCR or CSCR, LASCR (light activated SCR), LAS (light activated switch) and LASCS (light activated SCS).
This ppt provides a brief overview on thyristors commonly known as SCRs. V- I characteristics curve, triggering methods, protection methods, series and parallel operations of SCRs, applications are discussed in this slide.
Dc bridge types ,derivation and its applicationkaroline Enoch
The DC Bridge is used for measuring the unknown electrical resistance. This can be done by balancing the two legs of the bridge circuit. The value of one of the arm is known while the other of them is unknown
Field-effect transistor amplifiers provide an excellent voltage gain with the added feature of high input impedance. They are also low-power-consumption configurations with good frequency range and minimal size and weight.
JFETs, depletion MOSFETs, and MESFETs can be used to design amplifiers having similar voltage gains.
The depletion MOSFET (MESFET) circuit, however, has a much higher input impedance than a similar JFET configuration.
To turn on a Thyristor, there are various triggering methods in which a trigger pulse is applied at its Gate terminal. Similarly, there are various techniques to turn off a Thyristor, these techniques are called Thyristor Commutation Techniques.
These slides provide an elementary description of Power Electronics and its application domains. It also shows the different power devices and converters.
This article discusses different power electronics devices that are in use like power diodes, power thyristors, power transistors, IGBT, GTO, IGCT and others. This article will give a basic view of these devices and their operations.
The AC and DC bridge both are used for measuring the unknown parameter of the circuit. The AC bridge measures the unknown impedance of the circuit. The DC bridge measures the unknown resistance of the circuit.
The complete list of thyristor family members include diac (bidirectional diode thyristor), triac (bidirectional triode thyristor), SCR (silicon controlled rectifier), Shockley diode, SCS (silicon controlled switch), SBS (silicon bilateral switch), SUS (silicon unilateral switch) also known as complementary SCR or CSCR, LASCR (light activated SCR), LAS (light activated switch) and LASCS (light activated SCS).
This ppt provides a brief overview on thyristors commonly known as SCRs. V- I characteristics curve, triggering methods, protection methods, series and parallel operations of SCRs, applications are discussed in this slide.
Dc bridge types ,derivation and its applicationkaroline Enoch
The DC Bridge is used for measuring the unknown electrical resistance. This can be done by balancing the two legs of the bridge circuit. The value of one of the arm is known while the other of them is unknown
Field-effect transistor amplifiers provide an excellent voltage gain with the added feature of high input impedance. They are also low-power-consumption configurations with good frequency range and minimal size and weight.
JFETs, depletion MOSFETs, and MESFETs can be used to design amplifiers having similar voltage gains.
The depletion MOSFET (MESFET) circuit, however, has a much higher input impedance than a similar JFET configuration.
To turn on a Thyristor, there are various triggering methods in which a trigger pulse is applied at its Gate terminal. Similarly, there are various techniques to turn off a Thyristor, these techniques are called Thyristor Commutation Techniques.
These slides provide an elementary description of Power Electronics and its application domains. It also shows the different power devices and converters.
A Bipolar Junction Transistor is a three-terminal semiconductor device consisting of two p-n junctions which are able to amplify or magnify a signal. It is a current controlled device. The three terminals of the BJT are the base, the collector and the emitter. A BJT is a type of transistor that uses both electrons and holes as charge carriers
THIS ANALOG ELECTRONICS CIRCUIT PPT COVER ALL PORTION OF THIS SUBJECT.MODULE 1 DC ANALYSIS OF BJT AND FET ,D.C LOAD LINE,STABILIZATION TECHNIQUE
MODULE-2 AC ANALYSIS OF BJT
MODULE-3 OPERATIONAL AMPLIFIER,FEEDBACK TOPOLOGY,OSCILLATOR
THIS PPT i.e Analog Electronic Circuit (AEC) covered all the module i.e all the portion of this subject,module 1 all biasing technique of BJT And FET D.C. Analysis,stabilization technique,
Module 2 Ac analysis
Module 3 Operational Amplifier (OPAMP),Oscillator,Feedback concept
Bipolar Junction Transistor (BJT) DC and AC AnalysisJess Rangcasajo
BJT AC and DC Analysis
This slide condenses the two ways analysis of BJT (AC and DC).
At the end of the slide, it has review question answer with answer key as providing.
Pre Final Year project/ mini project for Electronics and communication engine...Shirshendu Das
Mini project for Electronics and communication engineering (ECE) to build an AC to DC power supply using Full Wave Rectifier having input as 220-240V AC and giving stable filtered output of 5V, -5V & variable 5V DC. Simulation of the circuit was done in Proteus design suite.
Orbits : types of satellites : frequency used link establishment, MA techniques used in satellite communication, earth station; aperture actuators used in satellite – Intelsat and Insat: fibers – types:
sources, detectors used, digital filters, optical link: power line carrier communications: SCADA
AM – Frequency spectrum – vector representation – power relations – generation of AM – DSB, DSB/SC, SSB, VSB AM Transmitter & Receiver; FM and PM – frequency spectrum – power relations : NBFM & WBFM, Generation of FM and DM, Armstrong method & Reactance modulations : FM & PM frequency.
PN junction diode –structure, operation and V-I characteristics, diffusion and transient capacitance - Rectifiers – Half Wave and Full Wave Rectifier,– Display devices- LED, Laser diodes- Zener diodecharacteristics-Zener Reverse characteristics – Zener as regulator,TRANSISTORS, BJT, JFET, MOSFET- structure, operation, characteristics and Biasing UJT, Thyristor and IGBT Structure and characteristics,BJT small signal model – Analysis of CE, CB, CC amplifiers- Gain and frequency response –
MOSFET small signal model– Analysis of CS and Source follower – Gain and frequency response- High frequency analysis,BIMOS cascade amplifier, Differential amplifier – Common mode and Difference mode analysis – FET input stages – Single tuned amplifiers – Gain and frequency response – Neutralization methods, power amplifiers –Types (Qualitative analysis),Advantages of negative feedback – voltage / current, series , Shunt feedback –positive feedback – Condition for oscillations, phase shift – Wien bridge, Hartley, Colpitts and Crystal oscillators.
Multinational Corporations – Environmental Ethics – Computer Ethics – Weapons Development – Engineers as Managers – Consulting Engineers – Engineers as Expert Witnesses and Advisors – Moral Leadership –Code of Conduct – Corporate Social Responsibility
Safety and Risk – Assessment of Safety and Risk – Risk Benefit Analysis and Reducing Risk - Respect for Authority – Collective Bargaining – Confidentiality – Conflicts of Interest – Occupational Crime – Professional Rights – Employee Rights – Intellectual Property Rights (IPR) – Discrimination
Senses of “Engineering Ethics” – Variety of moral issues – Types of inquiry – Moral dilemmas – Moral Autonomy – Kohlberg‟s theory – Gilligan‟s theory – Consensus and Controversy – Models of professional roles - Theories about right action – Self-interest – Customs and Religion – Uses of Ethical Theories
Morals, values and Ethics – Integrity – Work ethic – Service learning – Civic virtue – Respect for others – Living peacefully – Caring – Sharing – Honesty – Courage – Valuing time – Cooperation – Commitment – Empathy – Self confidence – Character – Spirituality – Introduction to Yoga and meditation for professional excellence and stress management.
Trust models for Grid security environment – Authentication and Authorization methods – Grid security infrastructure – Cloud Infrastructure security: network, host and application level – aspects of data security, provider data and its security, Identity and access management architecture, IAM practices in the cloud, SaaS, PaaS, IaaS availability in the cloud, Key privacy issues in the cloud.
Open source grid middleware packages – Globus Toolkit (GT4) Architecture , Configuration – Usage of Globus – Main components and Programming model - Introduction to Hadoop Framework - Mapreduce, Input splitting, map and reduce functions, specifying input and output parameters, configuring and running a job – Design of Hadoop file system, HDFS concepts, command line and java interface, dataflow of File read & File write.
Cloud deployment models: public, private, hybrid, community – Categories of cloud computing: Everything as a service: Infrastructure, platform, software - Pros and Cons of cloud computing – Implementation levels of virtualization – virtualization structure – virtualization of CPU, Memory and I/O devices – virtual clusters and Resource Management – Virtualization for data center automation.
How to Make a Field invisible in Odoo 17Celine George
It is possible to hide or invisible some fields in odoo. Commonly using “invisible” attribute in the field definition to invisible the fields. This slide will show how to make a field invisible in odoo 17.
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
This slides describes the basic concepts of ICT, basics of Email, Emerging Technology and Digital Initiatives in Education. This presentations aligns with the UGC Paper I syllabus.
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
Embracing GenAI - A Strategic ImperativePeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
Biological screening of herbal drugs: Introduction and Need for
Phyto-Pharmacological Screening, New Strategies for evaluating
Natural Products, In vitro evaluation techniques for Antioxidants, Antimicrobial and Anticancer drugs. In vivo evaluation techniques
for Anti-inflammatory, Antiulcer, Anticancer, Wound healing, Antidiabetic, Hepatoprotective, Cardio protective, Diuretics and
Antifertility, Toxicity studies as per OECD guidelines
Safalta Digital marketing institute in Noida, provide complete applications that encompass a huge range of virtual advertising and marketing additives, which includes search engine optimization, virtual communication advertising, pay-per-click on marketing, content material advertising, internet analytics, and greater. These university courses are designed for students who possess a comprehensive understanding of virtual marketing strategies and attributes.Safalta Digital Marketing Institute in Noida is a first choice for young individuals or students who are looking to start their careers in the field of digital advertising. The institute gives specialized courses designed and certification.
for beginners, providing thorough training in areas such as SEO, digital communication marketing, and PPC training in Noida. After finishing the program, students receive the certifications recognised by top different universitie, setting a strong foundation for a successful career in digital marketing.
1. EC6202 ELECTRONIC DEVICES AND CIRCUITS
Unit 2
Dr Gnanasekaran Thangavel
Professor and Head
Electronics and Instrumentation
Engineering
R M K Engineering College
2. UNIT II TRANSISTORS
BJT, JFET, MOSFET- structure, operation, characteristics
and Biasing UJT, Thyristor and IGBT Structure and
characteristics.
2 Dr Gnanasekaran Thangavel 8/2/2017
1. https://www.youtube.com/watch?v=yOmPCjPlaEg
2. https://www.youtube.com/watch?v=jQb199oIY5U
3. https://www.youtube.com/watch?v=G-BvuL5IDLw
4. https://www.youtube.com/watch?v=IRok_SGrx9Q
5. https://www.youtube.com/watch?v=2LBKwGwGYt4
6. https://www.youtube.com/watch?v=_DZ7baOhNFQ
7. https://www.youtube.com/watch?v=Dd4im8TMAk0
3. Bipolar Junction
transistor
Holes and electrons
determine device characteristics
Three terminal device
Control of two terminal
currents
Amplification and switching through 3rd contact
6. Transistor Construction
3 layer semiconductor device consisting:
2 n- and 1 p-type layers of material npn transistor
2 p- and 1 n-type layers of material pnp transistor
The term bipolar reflects the fact that holes and
electrons participate in the injection process into the
oppositely polarized material
A single pn junction has two different types of bias:
forward bias
reverse bias
Thus, a two-pn-junction device has four types of bias.
7. Position of the terminals and symbol of BJT.
• Base is located at the middle
and more thin from the level
of collector and emitter
• The emitter and collector
terminals are made of the
same type of semiconductor
material, while the base of the
other type of material
8. Transistor currents
-The arrow is always drawn
on the emitter
-The arrow always point
toward the n-type
-The arrow indicates the
direction of the emitter
current:
pnp:E B
npn: B E
IC=the collector current
IB= the base current
IE= the emitter current
9. By imaging the analogy of diode, transistor can be construct
like two diodes that connected together.
It can be conclude that the work of transistor is base on work of
diode.
11. Recall p-n junction
P N
W
Vappl > 0
-+
N P
W
Vappl < 0
-+
Forward bias, + on P, - on N
(Shrink W, Vbi)
Allow holes to jump over barrier
into N region as minority carriers
Reverse bias, + on N, - on P
(Expand W, Vbi)
Remove holes and electrons away
from depletion region
I
V
I
V
12. So if we combine these by fusing their
terminals…
P N
W
Vappl > 0
-+
N P
W
Vappl < 0
-+
Holes from P region (“Emitter”) of 1st PN junction
driven by FB of 1st PN junction into central N region (“Base”)
Driven by RB of 2nd PN junction from Base into P region of
2nd junction (“Collector”)
• 1st region FB, 2nd RB
• If we want to worry about holes alone, need P+ on 1st region
• For holes to be removed by collector, base region must be thin
18. 8/2/2017Dr Gnanasekaran Thangavel18
Active Region – the transistor operates as an amplifier and Ic = β.Ib
Saturation – the transistor is “Fully-ON” operating as a switch and Ic
= I(saturation)
Cut-off – the transistor is “Fully-OFF” operating as a switch and Ic =
0
Common Base Configuration – has Voltage Gain but no Current
Gain.
Common Emitter Configuration – has both Current and Voltage
Gain.
Common Collector Configuration – has Current Gain but no
Voltage Gain.
19. The Common Base (CB) Configuration
8/2/2017Dr Gnanasekaran Thangavel19
The input current flowing into the
emitter is quite large as its the sum
of both the base current and
collector current respectively
therefore, the collector current
output is less than the emitter
current input resulting in a current
gain for this type of circuit of “1”
(unity) or less, in other words the
common base configuration
“attenuates” the input signal.
This type of amplifier configuration is a non-inverting voltage amplifier
circuit, in that the signal voltages Vin and Vout are “in-phase”. Where:
Ic/Ie is the current gain, alpha ( α ) and RL/Rin is the resistance gain.
20. The Common Emitter (CE) Configuration
8/2/2017Dr Gnanasekaran Thangavel20
The common emitter amplifier
configuration produces the highest
current and power gain of all the three
bipolar transistor configurations. This
is mainly because the input
impedance is LOW as it is connected
to a forward biased PN-junction, while
the output impedance is HIGH as it is
taken from a reverse biased PN-
junction.
This type of bipolar transistor configuration has a greater input impedance, current
and power gain than that of the common base configuration but its voltage gain is
much lower. The common emitter configuration is an inverting amplifier circuit.
This means that the resulting output signal is 180o “out-of-phase” with the input
voltage signal.
21. The Common Collector (CC) Configuration
8/2/2017Dr Gnanasekaran Thangavel21
The common collector, or
emitter follower
configuration is very
useful for impedance
matching applications
because of the very high
input impedance, in the
region of hundreds of
thousands of Ohms while
having a relatively low
output impedance.
The common emitter configuration has a current gain approximately equal to the β
value of the transistor itself. In the common collector configuration the load
resistance is situated in series with the emitter so its current is equal to that of the
emitter current.
22. The Common Collector Current Gain
8/2/2017Dr Gnanasekaran Thangavel22
This type of bipolar transistor configuration
is a non-inverting circuit in that the signal
voltages of Vin and Vout are “in-phase”. It
has a voltage gain that is always less than
“1” (unity).
The load resistance of the common collector
transistor receives both the base and
collector currents giving a large current gain
(as with the common emitter configuration)
23. Bipolar Transistor Summary
8/2/2017Dr Gnanasekaran Thangavel23
Characteristic
Common
Base
Common
Emitter
Common
Collector
Input Impedance Low Medium High
Output Impedance Very High High Low
Phase Angle 0o 180o 0o
Voltage Gain High Medium Low
Current Gain Low Medium High
Power Gain Low Very High Medium
25. NPN Transistor Example
8/2/2017Dr Gnanasekaran Thangavel25
No1: A bipolar NPN transistor has a DC current gain, (Beta) value of 200.
Calculate the base current Ib required to switch a resistive load of 4mA.
Therefore, β = 200, Ic = 4mA and Ib = 20µA.
----------------------------------------------------------------------------------------------------------
------
No2 :An NPN Transistor has a DC base bias voltage, Vb of 10v and an input
base resistor, Rb of 100kΩ. What will be the value of the base current into the
transistor.
Therefore, Ib = 93µA.
26. Single Stage Common Emitter Amplifier
Circuit
8/2/2017Dr Gnanasekaran Thangavel26
Common Emitter Amplifier
configuration of an NPN
transistor is called a Class A
Amplifier. A “Class A Amplifier”
operation is one where the
transistors Base terminal is
biased in such a way as to
forward bias the Base-emitter
junction. Ohm´s Law, the
current flowing through the load
resistor, ( RL ),
27. Output Characteristics Curves of a Typical Bipolar
Transistor
8/2/2017Dr Gnanasekaran Thangavel27
Dynamic Load Line of the transistor can
be drawn directly onto the graph of
curves above from the point of
“Saturation” ( A ) when Vce = 0 to the
point of “Cut-off” ( B ) when Ic = 0 thus
giving us the “Operating” or Q-point of
the transistor. These two points are
joined together by a straight line and
any position along this straight line
represents the “Active Region” of the
transistor. The actual position of the
load line on the characteristics curves
can be calculated as follows:
28. Output Characteristics Curves of a Typical Bipolar
Transistor
8/2/2017Dr Gnanasekaran Thangavel28
Then, the collector or output characteristics curves
for Common Emitter NPN Transistors can be
used to predict the Collector current, Ic, when
given Vce and the Base current, Ib. A Load Line
can also be constructed onto the curves to
determine a suitable Operating or Q-point which
can be set by adjustment of the base current. The
slope of this load line is equal to the reciprocal of
the load resistance which is given as: -1/RL
Then we can define a NPN Transistor as being
normally “OFF” but a small input current and a
small positive voltage at its Base ( B ) relative to
its Emitter ( E ) will turn it “ON” allowing a much
large Collector-Emitter current to flow. NPN
transistors conduct when Vc is much greater than
31. 31
TRANSISTOR BIASING CIRCUITS
The term biasing is used for application of dc voltages to establish a fixed level of
current and voltage.
The purpose of biasing a circuit is to establish a proper stable dc operating point
(Q-point). The dc operating point between saturation and cutoff is called the Q-point.
The goal is to set the Q-point such that that it does not go into saturation or cutoff
when an ac signal is applied.
Transistor must be properly biased with dc voltage to operate as a linear amplifier.
If amplifier is not biased with correct dc voltages on input and output, it can go into
saturation or cutoff when the input signal applied.
There are several methods to establish DC operating point.
We will discuss some of the methods used for biasing transistors.
base-bias circuits
voltage-divider bias circuits
emitter-bias circuits
collector-feedback bias circuits
33. 33
A generic dc load line.
IC
VCE
(sat)
CC
C
C
V
I
R
(off )CE CCV V
CC CE
C
C
V V
I
R
34. 34
RB
RC
2 k
Q1
+12 V
VCE
2 4 6 8 10 12
2
4
6
8
IC
IC(sat)
VCE(off)
Plot the dc load line for the circuit shown in Fig. 7.3a.
35. 35
Fig 7.4 Example 7.2.
Plot the dc load line for the circuit shown in Fig. 7.4. Then,
find the values of VCE for IC = 1, 2, 5 mA respectively.
RB
RC
1 k
Q1
+10 V
VCE
2 4 6 8 10
2
4
6
8
IC
10 IC (mA) VCE (V)
1 9
2 8
5 5
CE CC C CV V I R
36. 36
Fig 7.6-8 Optimum Q-point with amplifier
operation.
βC BI I
CE CC C CV V I R
VCE
IB = 0 A
IB = 10 A
IB = 20 A
IB = 30 A
IB = 40 A
IB
= 50 A
IC
Q-Point
VCCVCC/2
IC(sat)
IC(sat)/2
IB
37. 37
Base bias (fixed bias).
CC BE
B
B
V V
I
R
βC BI I
CE CC C CV V I R
RC
RB
+0.7 V
IC
IB
IE
Input
Output
VBE
VCC
Q1
b = dc current gain = hFE
38. 38
Example
RC
2 k
RB
360 k
+0.7 V
IC
IB
IE
VBE
+8 V
hFE = 100
0.7V 8V 0.7V
360kΩ
20.28μA
CC
B
B
V
I
R
100 20.28μA
2.028mA
C FE BI h I
8V 2.028mA 2kΩ
3.94V
CE CC C CV V I R
The circuit is midpoint biased.
39. 39
Example
Construct the dc load line for the circuit shown in Fig. 7.10, and plot the Q-point
from the values obtained in Example 7.3. Determine whether the circuit is
midpoint biased.
VCE (V)
2 4 6 8 10
1
2
3
4
IC (mA)
Q
(sat)
8V
4mA
2kΩ
CC
C
C
V
I
R
off
8VCCCE
V V
40. 40
Example - Q-point shift.
The transistor in Fig. 7.12 has values of hFE = 100 when T = 25 °C and hFE = 150
when T = 100 °C. Determine the Q-point values of IC and VCE at both of these
temperatures.
RC
2 k
RB
360 k
+0.7 V
IC
IB
IE
VBE
+8 V
hFE = 100 (T = 25C)
hFE = 150 (T = 100C)
Temp(°C) IB (A) IC (mA) VCE (V)
25 20.28 2.028 3.94
100 20.28 3.04 1.92
41. 41
Base bias characteristics. (1)
RC
RB
+0.7 V
IC
IB
IE
Input
Output
VBE
VCC
Q1 Advantage: Circuit simplicity.
Disadvantage: Q-point shift with temp.
Applications: Switching circuits only.
Circuit recognition: A single resistor (RB) between
the base terminal and VCC. No emitter resistor.
42. 42
Base bias characteristics. (2)
RC
RB
+0.7 V
IC
IB
IE
Input
Output
VBE
VCC
Q1
(sat)
(off )
CC
C
C
CE CC
V
I
R
V V
Load line equations:
Q-point equations:
CC BE
B
B
C FE B
CE CC C C
V V
I
R
I h I
V V I R
43. 43
Voltage divider bias
R1
R2 RE
RC
+VCC
Input
Output
I1
I2 IE
IB
IC
Assume that I2 > 10IB.
2
1 2
B CC
R
V V
R R
0.7VE BV V
E
E
E
V
I
R
Assume that ICQ IE (or hFE >>
1). Then
CEQ CC CQ C EV V I R R
44. 44
Example -1
Determine the values of ICQ and VCEQ for the circuit shown in Fig. 7.15.
R1
18 k
R2
4.7 k
RE
1.1 k
RC
3 k
+10 V
I1
I2
IE
IB
IC
hFE = 50
2
1 2
4.7kΩ
10V 2.07V
22.7kΩ
B CC
R
V V
R R
0.7V
2.07V 0.7V 1.37V
E BV V
Because ICQ IE (or hFE >> 1),
1.37V
1.25mA
1.1kΩ
E
CQ
E
V
I
R
10V 1.25mA 4.1kΩ 4.87V
CEQ CC CQ C EV V I R R
45. 45
Example -2
Verify that I2 > 10 IB.
R1
18 k
R2
4.7 k
RE
1.1 k
RC
3 k
+10 V
I1
I2
IE
IB
IC
hFE = 50
2
2
2.07V
440.4μA
4.7kΩ
BV
I
R
1.25mA
1 50+1
24.51μA
E
B
FE
I
I
h
2 10 BI I
46. 46
Which value of hFE do I use?
Transistor specification sheet may list any combination of the
following hFE: max. hFE, min. hFE, or typ. hFE. Use typical value
if there is one. Otherwise, use
(ave) (min) (max)FE FE FEh h h
47. 47
Example
A voltage-divider bias circuit has the following values: R1 = 1.5 k, R2 =
680 , RC = 260 , RE = 240 and VCC = 10 V. Assuming the transistor is
a 2N3904, determine the value of IB for the circuit.
2
1 2
680Ω
10V 3.12V
2180Ω
B CC
R
V V
R R
0.7V 3.12V 0.7V 2.42VE BV V
2.42V
10mA
240Ω
E
CQ E
E
V
I I
R
( ) (min) (max) 100 300 173FE ave FE FEh h h
(ave)
10mA
57.5μA
1 174
E
B
FE
I
I
h
48. 48
Stability of Voltage Divider
Bias Circuit
The Q-point of voltage divider bias circuit is less dependent on hFE than
that of the base bias (fixed bias).
For example, if IE is exactly 10 mA, the range of hFE is 100 to 300. Then
10mA
At 100, 100μA and 9.90mA
1 101
E
FE B CQ E B
FE
I
h I I I I
h
10mA
At 300, 33μA and 9.97mA
1 301
E
FE B CQ E B
FE
I
h I I I I
h
ICQ hardly changes over the entire range of hFE.
49. 49
Load line for voltage divider bias circuit.
2 4 6 8 10 12
5
10
15
20
25
IC (mA)
VCE (V)
(sat)
10V
20mA
260Ω+240Ω
CC
C
C E
V
I
R R
(off ) 10VCE CCV V
Circuit values are from Example 7.9.
50. 50
Base input resistance - 1
R1
R2 RE
RC
VCC
I1
I2
IE
IB
IC
RIN(base)
R1
R2
I1
I2
VCC
0.7 V
IB RIN(base)
( 1)E E E B FE EV I R I h R
(base) ( 1)E
IN FE E
B
FE E
V
R h R
I
h R
May be ignored.
51. 51
Base input resistance -2
IB
R1
R2
I1
I2
VCC
IB RIN(base)
VB
2 (base)
1 2 (base)
2
1 2
21
//
//
//
//
//
IN
B CC
IN
FE E
CC
FE E
EQ
CC
EQ FE EEQ
R R
V V
R R R
R h R
V
R R h R
R
V
R R h RR R
52. 52
Example
2 //
10kΩ// 50 1.1kΩ 8.46kΩ
EQ FE ER R h R
1
8.46kΩ
20V 2.21V
68kΩ 8.46kΩ
EQ
B CC
EQ
R
V V
R R
0.7V
2.21V 0.7V
1.37mA
1.1kΩ
E B
CQ E
E E
V V
I I
R R
20V 1.37mA 7.3kΩ 9.99V
CEQ CC CQ C EV V I R R
R1
68k
R2
10k
RE
1.1k
RC
6.2k
VCC=20V
I1
I2
IE
IC
hFE = 50
53. 53
Voltage-divider bias characteristics - 1
R1
R2 RE
RC
+VCC
Input
Output
I1
I2 IE
IB
IC
Circuit recognition: The voltage
divider in the base circuit.
Advantages: The circuit Q-point values
are stable against changes in hFE.
Disadvantages: Requires more
components than most other biasing
circuits.
Applications: Used primarily to bias
linear amplifier.
54. 54
Voltage-divider bias characteristics -2
R1
R2 RE
RC
+VCC
Input
Output
I1
I2 IE
IB
IC
Load line
equations: (sat)
(off )
CC
C
C E
CE CC
V
I
R R
V V
Q-point equations (assume that
hFERE > 10R2):
2
1 2
0.7V
B CC
E B
E
CQ E
E
CEQ CC CQ C E
R
V V
R R
V V
V
I I
R
V V I R R
56. 56
Emitter bias.
Assume that the transistor operation is in
active region.
RC
RE
RB
IC
IE
IB
Q1
Input
Output
+VCC
-VEE
0.7V
1
EE
B
B FE E
V
I
R h R
C FE BI h I
1E FE BI h I
CE CC C C E E EEV V I R I R V
Assume that hFE >> 1.
CE CC C C E EEV V I R R V
57. 57
Example
RC
750
RE
1.5k
RB
100
IC
IE
IB
Q1
Input
Output
+12 V
-12 V
hFE = 200
Determine the values of
ICQ and VCEQ for the
amplifier shown in
Fig.7.27.
12V 0.7V
( 1)
11.3V
37.47μA
100Ω+201 1.5kΩ
B
B FE E
I
R h R
200 37.47μA
7.49mA
CQ FE BI h I
( )
24V 7.49mA 750Ω 1.5kΩ
7.14V
CEQ CC C C E EEV V I R R V
58. 58
Load Line for
Emitter-Bias Circuit
(sat)
( )CC EE CC EE
C
C E C E
V V V V
I
R R R R
( )CE off CC EE CC EEV V V V V
VCE
IC
IC(sat)
VCE(off)
59. 59
Emitter-bias characteristics -1
RC
RE
RB
IC
IE
IB
Q1
Input
Output
+VCC
-VEE
Circuit recognition: A split (dual-polairty) power
supply and the base resistor is connected to
ground.
Advantage: The circuit Q-point values are stable
against changes in hFE.
Disadvantage: Requires the use of dual-polarity
power supply.
Applications: Used primarily to bias linear
amplifiers.
62. 62
Fig 7.30 Example 7.14.
Determine the values of ICQ and VCEQ for the amplifier shown
in Fig. 7.30.
RB
RC
1.5 k
+10 V
180 k
hFE = 100
1
10V 0.7V
28.05μA
180kΩ 101 1.5kΩ
CC BE
B
B FE C
V V
I
R h R
100 28.05μA
2.805mA
CQ FE BI h I
( 1)
10V 101 28.05μA 1.5kΩ
5.75V
CEQ CC FE B CV V h I R
63. 63
Circuit Stability of
Collector-Feedback Bias
RB
RC
+VCC
IC
IE
IB
hFE increases
IC increases (if IB is the same)
VCE decreases
IB decreases
IC does not increase that much.
Good Stability. Less dependent on hFE and
temperature.
64. 64
Collector-Feedback
Characteristics (1)
RB
RC
+VCC
IC
IE
IB
Circuit recognition: The base resistor is
connected between the base and the
collector terminals of the transistor.
Advantage: A simple circuit with relatively
stable Q-point.
Disadvantage: Relatively poor ac
characteristics.
Applications: Used primarily to bias linear
amplifiers.
67. 67
Fig 7.32 Example 7.15.
RB
680k
RC
6.2k
+VCC
RE
1.6k
hFE = 50
16V 0.7V
1 680kΩ 51 1.6kΩ
20.09μA
CC BE
B
B FE E
V V
I
R h R
50 20.09μA 1mACQ FE BI h I
16V 1mA 7.8kΩ 8.2V
CEQ CC CQ C EV V I R R
68. 68
Circuit Stability of
Emitter-Feedback Bias
hFE increases
IC increases (if IB is the same)
VE increases
IB decreases
IC does not increase that much.
IC is less dependent on hFE and temperature.
RB RC
+VCC
RE
IB
IE
IC
69. 69
Emitter-Feedback Characteristics -1
Circuit recognition: Similar to voltage
divider bias with R2 missing (or base bias
with RE added).
Advantage: A simple circuit with relatively
stable Q-point.
Disadvantage: Requires more components
than collector-feedback bias.
Applications: Used primarily to bias linear
amplifiers.
RB RC
+VCC
RE
IB
IE
IC
70. 70
Emitter-Feedback Characteristics -2
RB RC
+VCC
RE
IB
IE
IC
Q-point relationships:
( 1)
CC BE
B
B FE E
V V
I
R h R
CQ FE BI h I
CEQ CC CQ C EV V I R R
71. 71
Summary
DC Biasing and the dc load line
Base bias circuits
Voltage-divider bias circuits
Emitter-bias circuits
Feedback-bias circuits
Collector-feedback bias circuits
Emitter-feedback bias circuits
72. Field-Effect Transistors -FET
8/2/2017Dr Gnanasekaran Thangavel72
The FET is based around the concept that charge
on a nearby object can attract charges within a
semiconductor channel.
The FET consists of a semiconductor channel with
electrodes at either end referred to as the drain and
the source.
A control electrode called the gate is placed in very
close proximity to the channel so that its electric
charge is able to affect the channel
In this way, the gate of the FET controls the flow of
carriers (electrons or holes) flowing from the source
to drain. It does this by controlling the size and
shape of the conductive channel.
The semiconductor channel where the current flow
occurs may be either P-type or N-type. This gives
rise to two types or categories of FET known as P-
73. Field Effect Transistor types
8/2/2017Dr Gnanasekaran Thangavel73
There are many ways to define the
different types of FET that are available.
They may be categorised in a number of
ways, but some of the major types of FET
can be covered in the tree diagram.
Junction FET(JFET), Insulated Gate
FET(IGFET), Metal Oxide Silicon
FET(MOSFET), Dual Gate
MOSFET(DGMOSFET), MEtal Silicon
FET(MESFET), High Electron Mobility
Transistor (HEMT) , Pseudomorphic High
Electron Mobility Transistor( PHEMT), Fin
Field Effect Transistor (FinFET), vertical
MOS( VMOS)
74. 8/2/2017Dr Gnanasekaran Thangavel74
The N-channel JFET’s channel is doped with donor impurities meaning that
the flow of current through the channel is negative (hence the term N-
channel) in the form of electrons.
The P-channel JFET’s channel is doped with acceptor impurities meaning
that the flow of current through the channel is positive (hence the term P-
channel) in the form of holes. N-channel JFET’s have a greater channel
conductivity (lower resistance) than their equivalent P-channel types, since
electrons have a higher mobility through a conductor compared to holes.
This makes the N-channel JFET’s a more efficient conductor compared to
their P-channel counterparts.
Bipolar Transistor
Field Effect
Transistor
Emitter – (E) >> Source –
(S)
Base – (B) >> Gate –
(G)
75. Biasing of an N-channel JFET
8/2/2017Dr Gnanasekaran Thangavel75
The cross sectional diagram above shows an
N-type semiconductor channel with a P-type
region called the Gate diffused into the N-
type channel forming a reverse biased PN-
junction and it is this junction which forms the
depletion region around the Gate area when
no external voltages are applied. JFETs are
therefore known as depletion mode devices.
76. JFET Channel Pinched-off
8/2/2017Dr Gnanasekaran Thangavel76
The width of the channel decreases until no
more current flows between the Drain and
the Source and the FET is said to be
“pinched-off” (similar to the cut-off region for
a BJT). The voltage at which the channel
closes is called the “pinch-off voltage”, ( VP ).
In this pinch-off region the Gate voltage, VGS
controls the channel current and VDS has
little or no effect.
The result is that the FET acts more like a
voltage controlled resistor which has zero
resistance when VGS = 0 and maximum “ON”
resistance ( RDS ) when the Gate voltage is
very negative. Under normal operating
conditions, the JFET gate is always
negatively biased relative to the source.
JFET
Model
77. Output characteristic V-I curves of a typical
junction FET.
8/2/2017Dr Gnanasekaran Thangavel77
The characteristics curves example shown above,
shows the four different regions of operation for a JFET
and these are given as:
Ohmic Region – When VGS = 0 the depletion layer of
the channel is very small and the JFET acts like a
voltage controlled resistor.
Cut-off Region – This is also known as the pinch-off
region were the Gate voltage, VGS is sufficient to
cause the JFET to act as an open circuit as the
channel resistance is at maximum.
Saturation or Active Region – The JFET becomes a
good conductor and is controlled by the Gate-Source
voltage, ( VGS ) while the Drain-Source voltage, ( VDS
) has little or no effect.
Breakdown Region – The voltage between the Drain
and the Source, ( VDS ) is high enough to causes the
78. This another type of Field Effect Transistor
available whose Gate input is electrically
insulated from the main current carrying
channel and is therefore called an Insulated
Gate Field Effect Transistor or IGFET.
The most common type of insulated gate FET
which is used in many different types of
electronic circuits is called the Metal Oxide
Semiconductor Field Effect Transistor or
MOSFET for short.
The IGFET or MOSFET is a voltage
controlled field effect transistor that differs
from a JFET in that it has a “Metal Oxide”
Gate electrode which is electrically insulated
Metal Oxide Semiconductor Field Effect-MOSFET
79. Like the previous JFET tutorial, MOSFETs are three terminal devices
with a Gate, Drain and Source and both P-channel (PMOS) and N-
channel (NMOS) MOSFETs are available. The main difference this
time is that MOSFETs are available in two basic forms:
Depletion Type – the transistor requires the Gate-Source voltage,
( VGS ) to switch the device “OFF”. The depletion mode MOSFET is
equivalent to a “Normally Closed” switch.
Enhancement Type – the transistor requires a Gate-Source
voltage, ( VGS ) to switch the device “ON”. The enhancement mode
MOSFET is equivalent to a “Normally Open” switch.
80. The four MOSFET symbols above show an
additional terminal called the Substrate and is
not normally used as either an input or an output
connection but instead it is used for grounding
the substrate. It connects to the main
semiconductive channel through a diode junction
to the body or metal tab of the MOSFET. Usually
in discrete type MOSFETs, this substrate lead is
connected internally to the source terminal.
When this is the case, as in enhancement types
it is omitted from the symbol for clarification.
The line between the drain and source
connections represents the semiconductive
channel. If this is a solid unbroken line then this
represents a “Depletion” (normally-ON) type
MOSFET as drain current can flow with zero
gate potential. If the channel line is shown dotted
or broken it is an “Enhancement” (normally-OFF)
type MOSFET as zero drain current flows with
zero gate potential. The direction of the arrow
indicates whether the conductive channel is a p-
81. Basic MOSFET Structure and Symbol MOSFET
construction
The construction of the Metal Oxide Semiconductor FET is
very different to that of the Junction FET. Both the
Depletion and Enhancement type MOSFETs use an
electrical field produced by a gate voltage to alter the flow
of charge carriers, electrons for n-channel or holes for P-
channel, through the semiconductive drain-source
channel. The gate electrode is placed on top of a very thin
insulating layer and there are a pair of small n-type regions
just under the drain and source electrodes.
We saw in the previous tutorial, that the gate of a junction
field effect transistor, JFET must be biased in such a way
as to reverse-bias the pn-junction. With a insulated gate
MOSFET device no such limitations apply so it is possible
to bias the gate of a MOSFET in either polarity, positive
(+ve) or negative (-ve).
This makes the MOSFET device especially valuable as
electronic switches or to make logic gates because with no
bias they are normally non-conducting and this high gate
input resistance means that very little or no control current
82. Depletion-mode MOSFET
The Depletion-mode MOSFET, which is less common than the enhancement
mode types is normally switched “ON” (conducting) without the application of a
gate bias voltage. That is the channel conducts when VGS = 0 making it a
“normally-closed” device. The circuit symbol shown above for a depletion MOS
transistor uses a solid channel line to signify a normally closed conductive
channel.
For the n-channel depletion MOS transistor, a negative gate-source voltage, -
VGS will deplete (hence its name) the conductive channel of its free electrons
switching the transistor “OFF”. Likewise for a p-channel depletion MOS
transistor a positive gate-source voltage, +VGS will deplete the channel of its
free holes turning it “OFF”.
In other words, for an n-channel depletion mode MOSFET: +VGS means more
electrons and more current. While a -VGS means less electrons and less
current. The opposite is also true for the p-channel types. Then the depletion
mode MOSFET is equivalent to a “normally-closed” switch.
83. Depletion-mode N-Channel MOSFET and circuit
Symbols
The depletion-mode MOSFET is
constructed in a similar way to their
JFET transistor counterparts were
the drain-source channel is
inherently conductive with the
electrons and holes already present
within the n-type or p-type channel.
This doping of the channel
produces a conducting path of low
resistance between the Drain and
Source with zero Gate bias.
84. Enhancement-mode MOSFET
The more common Enhancement-mode MOSFET or eMOSFET, is the reverse of the depletion-mode
type. Here the conducting channel is lightly doped or even undoped making it non-conductive. This
results in the device being normally “OFF” (non-conducting) when the gate bias voltage, VGS is equal
to zero. The circuit symbol shown above for an enhancement MOS transistor uses a broken channel
line to signify a normally open non-conducting channel.
For the n-channel enhancement MOS transistor a drain current will only flow when a gate voltage ( VGS
) is applied to the gate terminal greater than the threshold voltage ( VTH ) level in which conductance
takes place making it a transconductance device.
The application of a positive (+ve) gate voltage to a n-type eMOSFET attracts more electrons towards
the oxide layer around the gate thereby increasing or enhancing (hence its name) the thickness of the
channel allowing more current to flow. This is why this kind of transistor is called an enhancement mode
device as the application of a gate voltage enhances the channel.
Increasing this positive gate voltage will cause the channel resistance to decrease further causing an
increase in the drain current, ID through the channel. In other words, for an n-channel enhancement
mode MOSFET: +VGS turns the transistor “ON”, while a zero or -VGS turns the transistor “OFF”. Then,
the enhancement-mode MOSFET is equivalent to a “normally-open” switch.
The reverse is true for the p-channel enhancement MOS transistor. When VGS = 0 the device is “OFF”
and the channel is open. The application of a negative (-ve) gate voltage to the p-type eMOSFET
85. Enhancement-mode N-Channel MOSFET and Circuit
Symbols
Enhancement-mode MOSFETs
make excellent electronics
switches due to their low “ON”
resistance and extremely high
“OFF” resistance as well as their
infinitely high input resistance due
to their isolated gate.
Enhancement-mode MOSFETs are
used in integrated circuits to
produce CMOS type Logic Gates
and power switching circuits in the
form of as PMOS (P-channel) and
NMOS (N-channel) gates. CMOS
actually stands for Complementary
MOS meaning that the logic device
86. Enhancement-mode N-Channel MOSFET
Amplifier
The DC biasing of this
common source (CS)
MOSFET amplifier circuit
is virtually identical to the
JFET amplifier. The
MOSFET circuit is biased
in class A mode by the
voltage divider network
formed by resistors R1
and R2. The AC input
resistance is given as RIN
= RG = 1MΩ.
87. Enhancement-mode N-Channel MOSFET
Amplifier …
Metal Oxide Semiconductor Field Effect Transistors are three terminal active
devices made from different semiconductor materials that can act as either an
insulator or a conductor by the application of a small signal voltage. The
MOSFETs ability to change between these two states enables it to have two basic
functions: “switching” (digital electronics) or “amplification” (analogue electronics).
Then MOSFETs have the ability to operate within three different regions:
1. Cut-off Region – with VGS < Vthreshold the gate-source voltage is lower
than the threshold voltage so the MOSFET transistor is switched “fully-OFF” and
IDS = 0, the transistor acts as an open circuit
2. Linear (Ohmic) Region – with VGS > Vthreshold and VDS < VGS the
transistor is in its constant resistance region and behaves as a voltage-controlled
resistor whose resistive value is determined by the gate voltage, VGS
3. Saturation Region – with VGS > Vthreshold the transistor is in its constant
current region and is switched “fully-ON”. The current IDS = maximum as the
88. MOSFET Summary
MOSFET type VGS = +ve VGS = 0
VGS = -
ve
N-Channel Depletion ON ON OFF
N-Channel
Enhancement
ON OFF OFF
P-Channel Depletion OFF ON ON
P-Channel
Enhancement
OFF OFF ON
90. INTRODUCTION:
The SCR is the most important special semiconductor device. This device is
popular for its Forward-Conducting and Reverse-blocking
characteristics.
SCR can be used in high-power devices. For example, in the central
processing unit of the computer, the SCR is used in switch mode power
supply (SMPS).
The DIAC, a combination of two Shockley Diodes, and the TRIAC, a
combination of two SCRs connected anti-parallelly are important power-
control devices.
The UJT is also used as an efficient switching device.
91. SILICON-CONTROLLED RECTIFIER (SCR)
The silicon-controlled rectifier or semiconductor controlled rectifier is
a two-state device used for efficient power control.
SCR is the parent member of the thyristor family and is used in high-
power electronics. Its constructional features, physical operation and
characteristics are explained in the following sections.
The SCR is a four-layer structure, either p–n–p–n or n–p–n–p, that
effectively blocks current through two terminals until it is turned ON by a
small-signal at a third terminal.
The SCR has two states: a high-current low-impedance ON state and a
low-current high-impedance OFF state.
The basic transistor action in a four-layer p–n–p–n structure is analyzed
first with only two terminals, and then the third control input is introduced.
92. Physical Operation and Characteristics:
The physical operation of the SCR can be explained clearly with reference to
the current–voltage characteristics.
The forward-bias condition and reverse-bias condition illustrate the
conducting state and the reverse blocking state respectively. Based on these
two states a typical I –V characteristic of the SCR is shown in Fig. 8-2.
93. SCR in Forward Bias:
There are two different states in which we can examine the SCR in the forward-
biased condition:
(i) The high- impedance or forward-blocking state
(ii) The low-impedance or forward-conducting state
At a critical peak forward voltage Vp, the SCR switches from the blocking state to
the conducting state, as shown in Fig. 8-2.
A positive voltage places junction j1 and j3 under forward-bias, and the centre
junction j2 under reverse-bias.
The for ward voltage in the blocking state appears across the reverse-biased
junction j2 as the applied voltage V is increased. The voltage from the anode A to
cathode C, as shown in Fig. 8-1, is very small after switching to the forward-
conducting state, and all three junctions are forward-biased. The junction j2
switches from reverse-bias to forward-bias..
94. SCR in Reverse Bias:
In the reverse-blocking state the junctions j1 and j3 are reverse-
biased, and j2 is forward-biased.
The supply of electrons and holes to junction j2 is restricted, and due
to the thermal generation of electron–hole pairs near junctions j1 and j2 the
device current is a small saturation current.
In the reverse blocking condition the current remains small until
avalanche breakdown occurs at a large reverse-bias of several thousand volts.
An SCR p–n–p–n structure is equivalent to one p–n–p transistor and
one n–p–n transistor sharing some common terminals.
Collector current I C 1 = α1i + I CO 1 having a transfer ratio α 1 for the p–n–p.
Collector current I C 2 =α2i + I CO 2 having a transfer ratio a2 for the n–p–n.
ICO1 and ICO 2 stand for the respective collector-saturation currents.
I C 1 = α 1i + I CO 1 = I B 2 ……………….(8-1)
96. The total current through the SCR is the sum of iC1 and iC2:
I C 1 + I = i ………………..(8-3)
Substituting the values of collector current from Eqs. (8-1) and (8-2) in Eq. (8-3) we get:
i (α1 + α2) + I CO 1 + I CO 2 = i
i = (I CO 1 + I CO 2 ) /(1- α1 + α2) ………………..(8-4)
Case I: When (α1 + α2) → 1, then the SCR current i → infinite.
As the sum of the values of alphas tends to unity, the SCR current i increases rapidly. The
derivation is no
longer valid as (α1 + α2) equals unity.
Case II: When (α1 + α2 → 0, i.e., when the summation value of alphas goes to zero, the
SCR resultant current can be expressed as:
i = I CO 1 + I CO 2 …………………………….(8-5)
The current, i, passing through the SCR is very small. It is the combined collector-saturation
currents of the two equivalent transistors as long as the sum (α1 + α2) is very small or almost
near zero.
SCR in Reverse Bias:
97. I–V Characteristics of the SCR:
Forward-Blocking State:
When the device is biased in the forward-blocking state, as shown in Fig. 8-4(a), the applied
voltage appears primarily across the reverse-biased junction j2. Al though the junctions j1 and j3 are
forward-biased, the current is small.
98. Forward-Conducting State of the SCR:
As the value of (α1 + α2 ) approaches unity through one of the mechanisms ,many holes
injected at j1 survive to be swept across j2 into p2.
This process helps feed the recombination in p2 and support the injection of holes into n2. In a
similar manner, the transistor action of electrons injected at j3 and collected at j2 supplies electrons for n1.
The current through the device can be much larger.
I–V Characteristics of the SCR:
99. Reverse-Blocking State of the SCR:
The SCR in reverse-biased condition allows almost negligible
current to flow through it. This is shown in Fig. 8-4(c).
In the reverse-blocking state of the SCR, a small saturation
current flows from anode to cathode. Holes will flow from the gate into p2, the base of the n–p–n transistor,
due to positive gate current.
The required gate current for turn-on is only a few milli-amperes, therefore, the SCR can be
turned on by a very small amount of power in the gate.
100. I–V Characteristics of the SCR:
As shown in Fig. 8-5, if the gate current is 0 mA, the
critical voltage is higher, i.e., the SCR requires more
voltage to switch to the conducting state.
But as the value of gate current increases, the critical
voltage becomes lower, and the SCR switches to
the conducting state at a lower voltage.
At the higher gate current IG2, the SCR switches
faster than at the lower gate current IG1,
because IG2 > IG1.
I–V Characteristics of the SCR:
101. Semiconductor-controlled switch (SCS):
Few SCRs have two gate leads, G2
attached to p2 and G1
attached to n1, as shown in Fig. 8-6.
This configuration is called the
semiconductor-controlled switch
(SCS).
The SCS, biased in the forward-
blocking state, can be switched to the
conducting state by a negative pulse at
the anode gate n1 or by a positive
current pulse applied to the cathode
gate at p2.
102. Simple Applications:
The SCR is the most important member of the thyristor family. The SCR is a
capable power device as it can handle thousands of amperes and volts.
Generally the SCR is used in many applications such as in high power
electronics, switches, power-control and conversion mode.
It is also used as surge protector.
Static Switch: The SCR is used as a switch for power-switching in various
control circuits.
Power Control: Since the SCR can be turned on externally, it can be used to
regulate the amount of power delivered to a load.
Surge Protection: In an SCR circuit, when the voltage rises beyond the
threshold value, the SCR is turned on to dissipate the charge or voltage quickly.
Power Conversion: The SCR is also used for high-power conversion and
regulation. This includes conversion of power source from ac to ac, ac to dc and
103. TRIODE AC SWITCH (TRIAC):
The term TRIAC is derived by combining the first three letters of the word
“TRIODE” and the word “AC”.
A TRIAC is capable of conducting in both the directions. The TRIAC, is thus, a
bidirectional thyristor with three terminals. It is widely used for the control of
power in ac circuits.
104. Constructional Features:
Depending upon the polarity of the gate pulse and the biasing
conditions, the main four-layer structure that turns ON by a
regenerative process could be one of p1 n1, p2 n2, p1 n1 p2 n3, or
p2 n1 p1 n4, as shown in Fig. 8-8.
105. Advantages of the TRIAC:
The TRIAC has the following advantages:
(i) They can be triggered with positive- or negative-polarity
voltage.
(ii) They need a single heat sink of slightly larger size.
(iii) They need a single fuse for protection, which simplifies their
construction.
(iv) In some dc applications, the SCR has to be connected with a
parallel diode for protection against reverse voltage, whereas a
TRIAC may work without a diode, as safe breakdown in either
direction is possible.
106. The TRIAC has the following disadvantages:
(i) TRIACs have low dv/dt ratings compared to SCRs.
(ii) Since TRIACs can be triggered in either direction, the trigger circuits with
TRIACs needs careful consideration.
(iii) Reliability of TRIACs is less than that of SCRs.
Disadvantages of the TRIAC:
Simple Applications of the TRIAC:
The TRIAC as a bidirectional thyristor has various applications. Some of the
popular applications of the
TRIAC are as follows:
(i) In speed control of single-phase ac series or universal motors.
(ii) In food mixers and portable drills.
(iii) In lamp dimming and heating control.
(iv) In zero-voltage switched ac relay.
107. DIODE AC SWITCH (DIAC):
The DIAC is a combination of two diodes. Diodes being unidirectional
devices, conduct current only in one direction.
If bidirectional (ac) operation is desired, two Shockley diodes may be joined
in parallel facing different directions to form the DIAC.
108. Constructional Features:
The construction of DIAC looks like a transistor but there are major differences.
They are as follows:
(i) All the three layers, p–n–p or n–p–n, are equally doped in the DIAC, whereas
in the BJT there is a gradation of doping. The emitter is highly doped, the collector
is lightly doped, and the base is moderately doped.
(ii) The DIAC is a two-terminal diode as opposed to the BJT, which is a three-
terminal device.
109. Physical Operation and Characteristics:
The main characteristics are of the DIAC are as follows:
(i) Break over voltage
(ii) Voltage symmetry
(iii) Break-back voltage
(iv) Break over current
(v) Lower power dissipation
Although most DIACs have symmetric switching voltages, asymmetric
DIACs are also available. Typical DIACs have a power dissipations
ranging from 1/2 to 1 watt.
111. UNIJUNCTION TRANSISTOR (UJT):
The uni-junction transistor is a three-terminal single-junction device. The switching
voltage of the UJT can be easily varied.
The UJT is always operated as a switch in oscillators, timing circuits and in
SCR/TRIAC trigger circuits.
112. Constructional Features:
The UJT structure consists of a lightly doped n-type silicon bar
provided with ohmic contacts on either side.
The two end connections are called base B1 and base B2. A small
heavily doped p-region is alloyed into one side of the bar. This p-region
is the UJT emitter (E) that forms a p–n junction with the bar.
Between base B1 and base B2, the resistance of the n-type bar called
inter-base resistance (RB ) and is in the order of a few kilo ohm.
This inter-base resistance can be broken up into two resistances—the
resistance from B1 to the emitter is RB1 and the resistance from B2 to
the emitter is RB 2.
Since the emitter is closer to B2 the value of RB1is greater than RB2.
Total resistance is given by:
113. Equivalent circuit for UJT:
The VBB source is generally
fixed and provides a constant
voltage from B2 to B1.
The UJT is normally
operated with both B2 and E
positive biased relative to B1.
B1 is always the UJT
reference terminal and all
voltages are measured
relative to B1 . VEE is a
variable voltage source.
115. ON State of the UJT Circuit:
As VEE increases, the UJT stays in the OFF state until VE approaches the
peak point value V P. As VE approaches VP the p–n junction becomes forward-
biased and begins to conduct in the opposite direction.
As a result IE becomes positive near the peak point P on the VE - IE curve.
When VE exactly equals VP the emitter current equals IP .
At this point holes from the heavily doped emitter are injected into the n-type
bar, especially into the B1 region. The bar, which is lightly doped, offers very
little chance for these holes to recombine.
The lower half of the bar becomes replete with additional current carriers
(holes) and its resistance RB is drastically reduced; the decrease in BB1
causes Vx to drop.
This drop, in turn, causes the diode to become more forward-biased and IE
116. OFF State of the UJT Circuit:
When a voltage VBB is applied across the two base terminals B1 and
B2, the potential of point p with respect to B1 is given by:
VP =[VBB/ (RB1 +RB2)]*RB1=η*RB1,
η is called the intrinsic stand off ratio with its typical value lying between
0.5 and 0.8.
The VEE source is applied to the emitter which is the p-side. Thus, the
emitter diode will be reverse-biased as long as VEE is less than Vx.
This is OFF state and is shown on the VE - IE curve as being a very
low current region.
In the OFF the UJT has a very high resistance between E and B1, and
IE is usually a negligible reverse leakage current. With no IE, the drop
across RE is zero and the emitter voltage equals the source voltage.
117. UJT Ratings:
Maximum peak emitter current : This represents the maximum allowable value of a pulse
of emitter current.
Maximum reverse emitter voltage :This is the maxi mum reverse-bias that the emitter
base junction B2 can tolerate before breakdown occurs.
Maximum inter base voltage :This limit is caused by the maxi mum power that the n-type
base bar can safely dissipate.
Emitter leakage current :This is the emitter current which flows when VE is less than Vp
and the UJT is in the OFF state.
The UJT is very popular today mainly due to its high switching speed.
A few select applications of the UJT are as follows:
(i) It is used to trigger SCRs and TRIACs
(ii) It is used in non-sinusoidal oscillators
(iii) It is used in phase control and timing circuits
(iv) It is used in saw tooth generators
(v) It is used in oscillator circuit design
Applications:
119. The insulated-gate bipolar transistor is a recent model of a power-switching
device that combines the advantages of a power BJT and a power MOSFET.
Both power MOSFET and IGBT are the continuously controllable voltage-
controlled switch.
Constructional Features:
The structure of an IGBT cell is shown in Fig. 8-19.
The p region acts as a substrate which forms the anode region, i.e., the
collector region of the IGBT. Then there is a buffer layer of n region and a
bipolar-base drift region.
The p-region contains two n regions and acts as a MOSFET source. An
inversion layer can be formed by applying proper gate voltage.
The cathode, i.e., the IGBT emitter is formed on the n source region.
INSULATED-GATE BIPOLAR TRANSISTOR
(IGBT):
120. Physical Operation:
The principle behind the operation of an
IGBT is similar to that of a power MOSFET.
The IGBT operates in two modes:
(i) The blocking or non-conducting
mode
(ii) The ON or conducting mode.
The circuit symbol for the IGBT is shown in
Fig. 8-20.
It is similar to the symbol for an n–p–n
bipolar-junction power transistor with the
121. REAL-LIFE APPLICATIONS:
The IGBT is mostly used in high-speed switching devices. They have
switching speeds greater than those of bipolar power transistors.
The turn-on time is nearly the same as in the case of a power
MOSFET, but the turn-off time is longer.
Thus, the maximum converter switching frequency of the IGBT is
intermediate between that of a bipolar power transistor and a power
MOSFET.
122. POINTS TO REMEMBER:
1. A thyristor is a multilayer p–n terminal electronic device used for bi-stable
switching.
2. The SCR has two states:
(a) High-current low-impedance ON state
(b) Low-current OFF state
3. Latching current is defined as a minimum value of anode current which is a
must in order to attain the turn-on process required to maintain conduction
when the gate signal is removed.
4. Holding current is defined as a minimum value of anode current below which
it must fall for turning off the thyristor..
5. The TRIAC is a bidirectional thyristor with three terminals. It is used
extensively for the control of power in ac circuits.
123. 7. Applications of the UJT:
(a) As trigger mechanism in the SCR and the TRIAC
(b) As non-sinusoidal oscillators
(c) In saw-tooth generators
(d) In phase control and timing circuits
8. The UJT operation can be stated as follows:
(a) When the emitter diode is reverse-biased, only a very small emitter
current flows. Under this condition RB1 is at its normal high-value. This is the OFF
state of the UJT.
(b) When the emitter diode becomes forward-biased RB1 drops to a very low
value so that the total resistance between E and B1 becomes very low, allowing
emitter current to flow readily. This is the ON state.
9. The IGBT is mostly used in high-speed switching Devices.
POINTS TO REMEMBER:
124. References
1. David A. Bell ,”Electronic Devices and Circuits”, Prentice Hall of India,.
2. www.ee.ic.ac.uk/fobelets/EE2BJT_1_Q.ppt
3. www.ohio.edu/people/starzykj/network/Class/.../Lecture11%20BJT%20Transistor.ppt
4. https://www.calvin.edu/~pribeiro/courses/engr311/Lecture%20Notes/Chap5.ppt
5. http://www.electronics-tutorials.ws/transistor/tran_1.html
6. http://www.electronics-tutorials.ws/transistor/tran_5.html
7. http://www.electronics-tutorials.ws/transistor/tran_6.html
8. http://www.electronic-circuits-diagrams.com/powerful-am-transmitter-circuit/
9. http://www.circuitstoday.com/single-transistor-radio
10. http://www.radio-electronics.com/info/data/semicond/fet-field-effect-transistor/fet-overview-
types.php
11. http://www.electronics-tutorials.ws/power/unijunction-transistor.html
12. users.prf.jcu.cz/klee/UAI609/documentation/transistor%20biasing.ppt
13. wps.pearsoned.com/wps/media/objects/11427/11702257/Chapter%2B8.ppt
124 Dr Gnanasekaran Thangavel 8/2/2017