EST 130, Transistor Biasing and Amplification.CKSunith1
The attached narrated power point presentation explains the need for biasing in transistor amplifiers and the different biasing arrangements used in transistor circuits. The material will be useful for KTU first year B Tech students who prepare for the subject EST 130, Part B, Basic Electronics Engineering.
EST 130, Transistor Biasing and Amplification.CKSunith1
The attached narrated power point presentation explains the need for biasing in transistor amplifiers and the different biasing arrangements used in transistor circuits. The material will be useful for KTU first year B Tech students who prepare for the subject EST 130, Part B, Basic Electronics Engineering.
Introduction to operational Amplifier. For A2 level physics (CIE). Discusses characteristics of op amp, inverting and non inverting amplifier, and voltage follower, and transfer characetristics, virtual earth , etc
Negative amplifiers and its types Positive feedback and Negative feedbackimtiazalijoono
Negative amplifiers
What is Feedback?
Positive feedback
Negative feedback
Feedback Circuit
Principles of Negative Voltage Feedback In Amplifiers
Gain of Negative Voltage Feedback Amplifier
Advantages of Negative Voltage Feedback
Principles of Negative Current Feedback
Current Gain with Negative Current Feedback
The performance obtainable from a single-stage amplifier is often insufficient for many applications, hence several stages may be combined forming a multistage amplifier. These stages are connected in cascade, i.e. output of the first stage is connected to form input of second stage, whose output becomes input of third stage, and so on.
thank u
Hansraj MEENA
This Presentation Of Classes Of Amplifiers which is based on class a b ab and c amplifier by Arsalan Qureshi student of Dawood University Roll no: D-16-TE-09.
RF Carrier oscillator
To generate the carrier signal.
Usually a crystal-controlled oscillator is used.
Buffer amplifier
Low gain, high input impedance linear amplifier.
To isolate the oscillator from the high power amplifiers.
Modulator : can use either emitter collector modulation
Intermediate and final power amplifiers (pull-push modulators)
Required with low-level transmitters to maintain symmetry in the AM envelope
Coupling network
Matches output impedance of the final amplifier to the transmission line/antenn
Applications are in low-power, low-capacity systems : wireless intercoms, remote control units, pagers and short-range walkie-talkie
Modulating signal is processed similarly as in low-level transmitter except for the addition of power amplifier
Power amplifier
To provide higher power modulating signal necessary to achieve 100% modulation (carrier power is maximum at the high-level modulation point).
Same circuit as low-level transmitter for carrier oscillator, buffer and driver but with addition of power amplifier
Using Chebyshev filter design, there are two sub groups,
Type-I Chebyshev Filter
Type-II Chebyshev Filter
The major difference between butterworth and chebyshev filter is that the poles of butterworth filter lie on the circle while the poles of chebyshev filter lie on ellipse.
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.
Introduction to operational Amplifier. For A2 level physics (CIE). Discusses characteristics of op amp, inverting and non inverting amplifier, and voltage follower, and transfer characetristics, virtual earth , etc
Negative amplifiers and its types Positive feedback and Negative feedbackimtiazalijoono
Negative amplifiers
What is Feedback?
Positive feedback
Negative feedback
Feedback Circuit
Principles of Negative Voltage Feedback In Amplifiers
Gain of Negative Voltage Feedback Amplifier
Advantages of Negative Voltage Feedback
Principles of Negative Current Feedback
Current Gain with Negative Current Feedback
The performance obtainable from a single-stage amplifier is often insufficient for many applications, hence several stages may be combined forming a multistage amplifier. These stages are connected in cascade, i.e. output of the first stage is connected to form input of second stage, whose output becomes input of third stage, and so on.
thank u
Hansraj MEENA
This Presentation Of Classes Of Amplifiers which is based on class a b ab and c amplifier by Arsalan Qureshi student of Dawood University Roll no: D-16-TE-09.
RF Carrier oscillator
To generate the carrier signal.
Usually a crystal-controlled oscillator is used.
Buffer amplifier
Low gain, high input impedance linear amplifier.
To isolate the oscillator from the high power amplifiers.
Modulator : can use either emitter collector modulation
Intermediate and final power amplifiers (pull-push modulators)
Required with low-level transmitters to maintain symmetry in the AM envelope
Coupling network
Matches output impedance of the final amplifier to the transmission line/antenn
Applications are in low-power, low-capacity systems : wireless intercoms, remote control units, pagers and short-range walkie-talkie
Modulating signal is processed similarly as in low-level transmitter except for the addition of power amplifier
Power amplifier
To provide higher power modulating signal necessary to achieve 100% modulation (carrier power is maximum at the high-level modulation point).
Same circuit as low-level transmitter for carrier oscillator, buffer and driver but with addition of power amplifier
Using Chebyshev filter design, there are two sub groups,
Type-I Chebyshev Filter
Type-II Chebyshev Filter
The major difference between butterworth and chebyshev filter is that the poles of butterworth filter lie on the circle while the poles of chebyshev filter lie on ellipse.
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.
An Amplifier receives a signal from some pickup transducer or other input source and
provides a larger version of the signal to some output device or to another amplifier stage.
An input transducer signal is generally small (a few millivolts from a cassette or CD input or a
few microvolts from an antenna) and needs to be amplified sufficiently to operate an output
device (speaker or other power handling device). In small signal amplifiers, the main factors
are usually amplification linearity and magnitude of gain, since signal voltage and current are
small in a small-signal amplifier, the amount of power-handling capacity and power efficiency
are of little concern. A voltage amplifier provides voltage amplification primarily to increase
the voltage of the input signal. Large-signal or power amplifiers, on the other hand, primarily
provide sufficient power to an output load to drive a speaker or other power device, typically
a few watts to tens of watts. In the present chapter, we concentrate on those amplifier circuits
used to handle large-voltage signals at moderate to high current levels. The main features of
a large-signal amplifier are the circuit's power efficiency, the maximum amount of power that
the circuit is capable of handling, and the impedance matching to the output device. One
method used to categorize amplifiers is by class. Basically, amplifier classes represent the
amount the output signal varies over one cycle of operation for a full cycle of input signal. A
brief description of amplifier classes is provided next.
Modified Bidirectional Converter with Current Fed InverterIJPEDS-IAES
A bidirectional dc-dc converter with multiple outputs are concatenated with a
high frequency current source parallel resonant push pull inverter is
presented in this paper. The two outputs are added together and it is taken as
the input source for the inverter. The current source parallel resonant push
pull inverter implemented here with high frequency applications like
induction heating, Fluorescent lighting, Digital signal processing sonar. This
paper proposes a simple photovoltaic power system consists of a
bidirectional converter and a current fed inverter for regulating the load
variations. Solar power is used as the input source for the system. Simulation
of the proposed system is carried out in PSIM software and experimentally
verified the results.
Soft Switched Multi-Output Flyback Converter with Voltage DoublerIJPEDS-IAES
A novel multi-output voltage doubler circuit with resonant switching
technique is proposed in this paper. The resonant topology in the primary
side of the flyback transformer switches the device either at zero voltage or
current thus optimizing the switching devices by mitigating the losses. The
voltage doubler circuit introduced in the load side increases the voltage by
twice the value thereby increasing the load power and density. The proposed
Multi-output Isolated Converter removes the need for mutiple SMPS units
for a particular application. This reduces the size and weight of the
converters considerably leading to a greater payload. This paper aims at
optimizing the proposed converter with some design changes. The results
obtained from the hardware prototype are given in a comprehensive manner
for a 3.5W converter operating at output voltages of 5V and 3.3V at 50 kHz
switching frequency. The converter output is regulated with the PI controller
designed with SG3523 IC. The effects of load and line regulation for ±20%
variations are analyzed in detail.
In the case of class A amplifier, we have observed that the transistor conducts for
the full cycle of the input signal i.e. the conduction angle is 180◦. Although
the transistor conducts for the full cycle of the input signal, the power conversion
efficiency is poor in class A amplifier. In addition to that, a great deal of
distortion is introduced by the nonlinearity in the dynamic transfer characteristic
of the transistor. The power conversion efficiency can be improved by biasing
the transistor at cut off point on VCE axis and a great deal of the distortion
due to nonlinearity in dynamic transfer characteristic may be eliminated by
the push-pull configuration of the transistor as discussed in next section
Electronics and Communication Engineering is the Branch of Engineering. Electronics and Communication Engineering field requires an understanding of core areas including Engineering Graphics, Computer Programming,Electronics Devices and Circuits-I, Network Analysis, Signals and Systems, Communication Systems, Electromagnetics Engineering, Digital Signal Processing, Embedded Systems, Microprocessor and Computer Architecture. Ekeeda offers Online Mechanical Engineering Courses for all the Subjects as per the Syllabus. Visit : https://ekeeda.com/streamdetails/stream/Electronics-and-Communication-Engineering
Block diagram of a typical op-amp – characteristics of ideal and practical op-amp - parameters of opamp – inverting and non-inverting amplifier configurations - frequency response - circuit stability.
Forklift Classes Overview by Intella PartsIntella Parts
Discover the different forklift classes and their specific applications. Learn how to choose the right forklift for your needs to ensure safety, efficiency, and compliance in your operations.
For more technical information, visit our website https://intellaparts.com
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
Instead of buying and hoping for the best, we can use data science to help us predict which products may be good fits for us. It includes various function programs to do the above mentioned tasks.
Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
NO1 Uk best vashikaran specialist in delhi vashikaran baba near me online vas...Amil Baba Dawood bangali
Contact with Dawood Bhai Just call on +92322-6382012 and we'll help you. We'll solve all your problems within 12 to 24 hours and with 101% guarantee and with astrology systematic. If you want to take any personal or professional advice then also you can call us on +92322-6382012 , ONLINE LOVE PROBLEM & Other all types of Daily Life Problem's.Then CALL or WHATSAPP us on +92322-6382012 and Get all these problems solutions here by Amil Baba DAWOOD BANGALI
#vashikaranspecialist #astrologer #palmistry #amliyaat #taweez #manpasandshadi #horoscope #spiritual #lovelife #lovespell #marriagespell#aamilbabainpakistan #amilbabainkarachi #powerfullblackmagicspell #kalajadumantarspecialist #realamilbaba #AmilbabainPakistan #astrologerincanada #astrologerindubai #lovespellsmaster #kalajaduspecialist #lovespellsthatwork #aamilbabainlahore#blackmagicformarriage #aamilbaba #kalajadu #kalailam #taweez #wazifaexpert #jadumantar #vashikaranspecialist #astrologer #palmistry #amliyaat #taweez #manpasandshadi #horoscope #spiritual #lovelife #lovespell #marriagespell#aamilbabainpakistan #amilbabainkarachi #powerfullblackmagicspell #kalajadumantarspecialist #realamilbaba #AmilbabainPakistan #astrologerincanada #astrologerindubai #lovespellsmaster #kalajaduspecialist #lovespellsthatwork #aamilbabainlahore #blackmagicforlove #blackmagicformarriage #aamilbaba #kalajadu #kalailam #taweez #wazifaexpert #jadumantar #vashikaranspecialist #astrologer #palmistry #amliyaat #taweez #manpasandshadi #horoscope #spiritual #lovelife #lovespell #marriagespell#aamilbabainpakistan #amilbabainkarachi #powerfullblackmagicspell #kalajadumantarspecialist #realamilbaba #AmilbabainPakistan #astrologerincanada #astrologerindubai #lovespellsmaster #kalajaduspecialist #lovespellsthatwork #aamilbabainlahore #Amilbabainuk #amilbabainspain #amilbabaindubai #Amilbabainnorway #amilbabainkrachi #amilbabainlahore #amilbabaingujranwalan #amilbabainislamabad
TECHNICAL TRAINING MANUAL GENERAL FAMILIARIZATION COURSEDuvanRamosGarzon1
AIRCRAFT GENERAL
The Single Aisle is the most advanced family aircraft in service today, with fly-by-wire flight controls.
The A318, A319, A320 and A321 are twin-engine subsonic medium range aircraft.
The family offers a choice of engines
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptxR&R Consult
CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
An inspection had shown that a significant amount of hot flue gas was bypassing the boiler tubes, where the heat was supposed to be transferred.
R&R Consult conducted a CFD analysis, which revealed that 6.3% of the flue gas was bypassing the boiler tubes without transferring heat. The analysis also showed that the flue gas was instead being directed along the sides of the boiler and between the modules that were supposed to capture the heat. This was the cause of the reduced performance.
Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)
Power amplifiers
1. Power Amplifiers
Text Book:
[1] Jacob Millman, Cristos C. Halkias, “Integrated
Electronics: Analog and Digital Circuits and Systems”,
34th Reprint 2004, Tata-McGraw-Hill. Chapter: 18
[2] Robert Boylestad and Louis Nashelsky, “Electronic
Devices and Circuit theory”, Fifth Edition, Prentice-hall
of India Private Limited 1994. Chapter:16
[3] Albert Paul Malvino, “Electronic Principles”, Tata
McGraw-Hill, 1999. Chapter: 11
2. Amplifier:
An amplifier is an electronic device that increases voltage,
current or power of a signal.
According to the class of operation, the amplifiers can be
classified as:
(i)Class A, (ii) Class B, (iii) Class AB, and (iv) Class C.
Class A: A class A
amplifier is one in which
the operating point and the
input signal are such that
the current in the output
circuit flows at full times.
The output signal of class
A amplifiers varies for a
full 360o of the cycle.
3. Class B: A class B amplifier is one in which the operating point is at
an extreme end of its characteristic, so that the quiescent power is
very small. If the signal voltage is sinusoidal, amplification takes
place for only one-half a cycle.
A class B circuit provides an output signal varying over one-half the
input signal cycle, of for 180o of input signal.
Class AB: A class AB amplifier is one operating between the two
extremes defined for class A and class B. Hence the output signal is
zero for part but less than one-half of an input sinusoidal signal.
For class AB operation the output signal swing occurs between 180o
and 360o and is neither class A nor class B operation.
4. Class C: A class C amplifier is one in which the
operating point is chosen so that the output current (or
voltage) is zero for more than one-half of the input
sinusoidal signal cycle.
The output of a class C amplifier is biased for operation at
less than 180o of the cycle and will operate only with a
tuned (resonant) circuit which provides a full cycle of
operation for the tuned or resonant frequency.
5. Series-Fed Class AAmplifier
The fixed-bias circuit connection shown in Fig. 16.1 can be used
to discuss the main features of a class A amplifier.
The beta (b) of power transistor is generally less than 100, the
overall amplifier circuit using power transistors being capable of
handle large power or current not providing much voltage gain.
DC Bias
The dc bias set by VCC and RB fixes the dc base-bias current at
)1.16(
BR
BEVCCV
BI
with the collector current then being
with the collector-emitter voltage then
)2.16(BICI b
)3.16(CRCICCVCEV
6. To appreciate the importance of the dc bias the operation of the power
amplifier, consider the collector characteristic shown in Fig. 16.3.
A dc load line is drawn using the values of VCC and RC.
The intersection of the dc bias value of IB with the dc load line then
determines the operating point (Q-point) for the circuit.
The quiescent-point values are those calculated using Eqs. (16.1)
through (16.3).
If the dc bias collector current is set at
one-half the possible signal swing
(between 0 and VCC/RC) the largest
collector current swing will be possible.
Additionally, if the quiescent collector-
emitter voltage is set at one-half the
supply voltage, the largest voltage
swing (between 0 and VCC) will be
possible.
7. When an input ac signal is applied to the amplifier of Fig. 16.1, the
output will vary from its dc bias operating voltage and current.
A small input signal, as shown in Fig. 16.4(a), will cause the base
current to vary above and below the dc bias point, which will then
cause the collector current (output) to vary from the dc bias point set as
well as the collector-emitter voltage to vary around its dc bias value.
AC Operation
Power Considerations
The input power with no input
signal drawn from the supply is
)4.16()dc( CQICCViP
Even with an ac signal applied, the
average current drawn from the
supply remains the same.
So Pi(dc) represent the input power.
8. Output Power
The output voltage and current varying around the bias point provide
ac power to the load.
The ac power is delivered to the load RC, in the circuit of Fig. 16.1 is
given by
)5.16(
)rms(2
)ac(
)5.16()rms(2)ac(
)5.16()rms()rms()ac(
c
CR
CEV
oP
bCRCIoP
aCICEVoP
:valuermsUsing
)5.16(
2
)p(2
)ac(
)5.16(
2
)p(2
)ac(
)5.16(
2
p)()p(
)ac(
c
CR
CEV
oP
b
CRCI
oP
aCICEV
oP
:valuepeakUsing
10. Maximum Efficiency
For the class A series amplifier the maximum efficiency can be
determined using the maximum voltage and current swings.
For the voltage swing it is
CR
CCV
CI
CCVCEV
)pp(Maximum
)pp(Maximum
Using the maximum voltage swing in Eq. (16.7c) yields
CR
CCV
CR
CCV
CCViP
2
2
2/
)dc(Maximum
CR
CCV
oP
8
2
)ac(Maximum
The maximum power input can be calculated using the dc bias
current set to half the maximum value.
Thus
11. We can then use Eq. (16.8) to calculate the maximum efficiency:
%25%100
8
2
%100
2
2
8
2
%100
)dc(maximum
)ac(maximum
%maximum
CCV
CR
CR
CCV
iP
oP
The maximum efficiency of a
class A amplifier is thus seen to
be 25%.
A form of class A amplifier
having maximum efficiency of
50% uses a transformer to couple
the output signal to the load as
shown in Fig. 16.6.
12. Example 16.1 Calculate the (i) base current, collector current and
collector to emitter voltage for the operating (or Q) point (ii) input
power, output power, and efficiency of the amplifier circuit in the
following figure for an input voltage in a base current of 10 mA peak.
Solution:
(i) the Q-point can be determined by DC
analysis as:
mA3.19
K1
V7.0V20V7.0
B
R
CC
V
Q
B
I
A48.0)mA3.19(25
B
I
C
I b
V4.10)20)(A48.0(V20
Q
CE
V
14. Class B Amplifier
Class B operation is provided when the dc bias transistor biased just
off, the transistor turning on when the ac signal is applied.
This is essentially no bias and the transistor conducts current for only
one-half of the signal cycle.
To obtain output for the full cycle of signal, it is necessary to use two
transistors and have each conduct on opposite half-cycles, the
combined operation providing a full cycle of output signal.
Since one part of the circuit pushes
the signal high during one-half
cycle and the other part pulls the
signal low during the other half-
cycle, the circuit is referred to as a
push-pull circuit.
Figure 16.12 shows a diagram for push-pull operation.
15. The arrangement of a push-pull circuit is shown in Fig. 18-8.
When the signal on transistor Q1 is positive, the signal on Q2 is
negative by an equal amount.
During the first half-cycle of operation, transistor Q1 is driven into
conduction, whereas transistor Q2 is driven off. The current i1 through
the transformer results in the first half-cycle of signal to the load.
During the second half-cycle of operation, transistor Q2 is driven into
conduction, whereas transistor Q1 is driven off. The current i2 through
the transformer results in the second half-cycle of signal to the load.
The overall signal developed across the load then varies over the full
cycle of signal operation.
16. Consider an input signal (base current) of the form ib1=Ibmcoswt applied
to Q1.
The output current of this transistor is given by Eq. (18.33):
)33.18(...........3cos
3
2cos
2
cos
101
tBtBtBB
C
Ii www
The corresponding input signal to Q2 is
)cos(
12
w t
bm
I
b
i
b
i
The output current of this transistor is obtained by replacing wt by
wt+ in the expression for ib1. That is,
)34.18()(
12
w tii
...........)(3cos
3
)(2cos
2
)cos(
102
Hence,
www tBtBtBB
C
Ii
)35.18(...........3cos
3
2cos
2
cos
102
iswhich
tBtBtBB
C
Ii www
17. The total output current is then proportional to the
difference between the collector current in the two
resistors. That is,
)36.18(.)..........3cos
3
cos
1
(2)
21
( tBtBkiiki ww
This expression shows that a push-pull circuit will balance
out all even harmonics in the output and will leave the
third-harmonic tram is the principle source of distortion.
This conclusion was reached on the assumption that the
two transistors are identical. If their characteristics differ
appreciably, the appearance of even harmonics must be
expected.
The fact that the output current contains no even-
harmonic.
18. Advantages of Push-Pull System
1) Push-pull circuit give more output per active device: Because no
even harmonics are present in the output of a push-pull amplifier, such
a circuit will give more output per active device for a given amount of
distortion. For the same reason, a push-pull arrangement may be used
to obtain less distortion for a given power output per transistor.
2) Eliminates any tendency toward core saturation and nonlinear
distortion of transformer: The dc components of the collector
current oppose each other magnetically in the transformer core. This
eliminates any tendency toward core saturation and consequent
nonlinear distortion that might arise from the curvature of the
transformer-magnetizing curve.
3) Ripple voltage will not appear in the load: The effects of ripple
voltages that may be contained in the power supply because of
inadequate filtering will be balance out. This cancellation results
because the currents produced by this ripple voltage are in oppose
directions in the transformer winding, and so will not appear in the
load.
19. Class B amplifier operation
The transistor circuit of Fig. 18-8 operates class B if R2=0 because a
silicon transistor is essentially at cutoff if the base is shorted to the
emitter.
Advantages of Class B as compared with class A operation
1. It is possible to obtain greater power output,
2. The efficiency is higher, and
3. There is negligible power loss at no signal.
Disadvantages of Class B as
compared with class A
operation
1. The harmonic distortion is
higher,
2. Self-bias cannot be used, and
3. The supply voltage must have
good regulation.
20. The graphical construction from which to determine the output current
and voltage waveshapes for a single transistor operating as a class B
stage is indicated in Fig. 18-9.
21. )17.16()dc( dcICCViP
Input power: The power supplied to the load by an amplifier is
drawn from the power supply which provides the input or dc power.
The amount of this power can be calculated using
)18.16()(
2
pI
dc
I
In class B operation the current drawn from a single power supply
has the same form of a full-wave rectified signal. So,
)19.16()p(
2
)dc(and ICCViP
Output Power: The output across the load is given by
)20.16(
)rms(2
)ac(
LR
LV
oP
)21.16(
8
)p-p(2
2
)p(2
)ac(
LR
LV
LR
LV
oP
22. Efficiency: The efficiency of the class B amplifier can be calculated
using the basic equation
%100
)dc(
)ac(
%
iP
oP
%100
)(22
)p(2
%
pICCVLR
LV
LR
LV
I
)p(
)p(using,
%100
)p(22
)p(2
%
LV
LR
CCVLR
LV
)22.16(%100
)p(
4
%
CCV
LV
23. Maximum Efficiency: Equation (16.22) shows that the larger the
peak voltage, the higher the circuit efficiency, up to a maximum value
when the , this maximum efficiency then being
LR
CCV
I )p(Maximum,
LR
CCV
dcI
2
Maximum,
LR
CCV
LR
CCV
CCViP
222
)dc(Maximum,
LR
CCV
oP
2
2
)ac(Maximum,
%5.78%100
4222
2
%Maximum,
CCV
LR
LR
CCV
The maximum efficiency of a class B amplifier is thus seen to be
78.5%.
24. Crossover distortion
The distortion caused by the nonlinear transistor input characteristic is
indicated in Fig. 18-12. The iB-vB curve for each transistor is drawn,
and the construction used to obtain the output current (assumed
proportional to the base current) is shown.
In the region of small currents (for vB<V) the output is much smaller
than it would be if the response were linear. This effect is called
crossover distortion.
In order to overcome the problem
of crossover distortion, the
transistor must operate in a class
AB mode.
25. (16.10) Calculate (i) the input power, (ii) the output power, (iii) the
power handled by each transistor, and (iv) the efficiency for an
input of 12 V (rms) of a push-pull Class-B amplifier circuit having
biasing voltage, VCC= 25 V and load resistance, RL= 4 .
Solution: Given, Vi (rms)=12V, VCC= 25 V, load resistance, RL= 4 .
V17V122)(2)( rmsiVpiV
Since, the operating point is selected in cutoff region, thus
Vi(p)=VL(p)=17V
4.25A
4
V17)(
)(
LR
pLV
pLI
A71.2A25.4
2
)(
2
dc
pLII
W75.67A25.4V25dc)dc( ICCViP
27. Class C Operation
With class B, we need to use a push-pull arrangement. That’s
why almost all class B amplifiers are push-pull amplifiers.
With class C, we need to use a resonant circuit for the load.
This is why almost all class C amplifiers are tuned amplifiers.
With class C operation, the collector current flows for less
than half a cycle.
A parallel resonant circuit can filter the pulses of collector
current and produce a pure sine wave of output voltage.
The main application for class C is with tuned RF amplifiers.
The maximum efficiency of a tuned class C amplifier is 100
percent.
28. Figure 11-13a shows a tuned RF amplifier.
The ac input voltage drives the base, and an amplified
output voltage appears at the collector.
The amplified and inverted signal is then capacitively
coupled to the load resistance.
Because of the parallel resonant circuit, the output voltage is
maximum at the resonant frequency, given by:
)14.11(
2
1
LC
rf
29. On either side of the resonant frequency fr, the voltage gain
drops as shown in Fig. 11-13b.
For this reason, a tuned class C amplifier is always intended
to amplify a narrow band of frequencies.
This makes it ideal for amplifying radio and television
signals because each station or channel is assigned a narrow
band of frequencies on both sides of a center frequency.