Power Amplifier circuits.
Output stages of types of power amplifier (class A, class B, class AB, class C, class D)
Distortions( Harmonic and Crossover).
Push-pull amplifier with and without transformer.
Complimentary symmetry and Quasi- complimentary symmetry push pull amplifier.
Class AB amplifiers combine aspects of Class A and Class B amplifiers. They are biased so both transistors conduct for small signals like Class A for lower distortion, and for large signals only one transistor conducts at a time like Class B for higher efficiency. The circuit uses a voltage divider and diodes to bias the transistors into slight conduction even without an input signal. This overcomes crossover distortion. The output operates with the Q-point slightly above cutoff and ac cutoff at the supply voltage for Class AB operation between Class A and Class B.
Power amplifiers are concerned with efficiency, maximum power capability, and impedance matching to the output device rather than small-signal factors like amplification, linearity, and gain. There are several classes of power amplifiers including Class A, B, AB, C, and D which differ based on the conduction angle of the output and location of the Q-point. Efficiency increases as the conduction angle decreases from Class A to Class B to Class C. Transformers can be used to improve efficiency and increase the output swing of Class A amplifiers. Push-pull configurations are used for Class B amplifiers to generate a full output cycle from two transistors.
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.
in this slide you will learn what are classes of amplifiers and what is main difference between all classes of amplifier
and after reading this slide you will be able to explain all clases of amplifier
The document summarizes different classes of power amplifiers: Class A amplifiers conduct through the full 360 degrees of the input signal with the Q-point set in the middle of the load line. Class B amplifiers conduct through 180 degrees of the input with the Q-point at 0V. Class AB is a compromise between A and B, conducting between 180-360 degrees with the Q-point between the midpoint and cutoff. Class C conducts less than 180 degrees with the Q-point below cutoff. Class D is biased for digital signals and has high efficiency.
A power amplifier is designed to provide maximum power output and is used to amplify weak signals to a level sufficient to drive a loudspeaker or other output device. It consists of multiple stages, with the final stage designed specifically for high power output. Power amplifiers use power transistors that can handle large currents and dissipate significant heat. They are classified based on the operating mode of the transistors, including class A, B, AB, and C power amplifiers. Transformer coupling is commonly used to match impedances in power amplifier circuits.
1. A multistage amplifier achieves greater voltage and power gain by using multiple amplification stages connected in cascade. The overall voltage gain is equal to the product of the individual stage gains.
2. Gain is often expressed in decibels (dB) which allows both small and large quantities to be conveniently represented on a logarithmic scale corresponding to human perception. The overall multistage amplifier gain in dB is the sum of the individual stage gains in dB.
3. Common types of coupling between stages include RC coupling using capacitors, direct coupling without coupling elements, and transformer coupling. RC coupling is inexpensive but limits low frequency response while direct coupling can amplify low frequencies without coupling elements.
This document discusses power amplifiers and class A amplifiers. It begins with an introduction to power amplifiers, including their purpose of delivering high power to low resistance loads. It then covers classification of amplifiers based on conduction angle and efficiency ratings. The document analyzes class A amplifiers in detail, including derivation of input power, output power, and efficiency equations. It shows the efficiency of class A amplifiers is limited to 25% theoretically due to continuous conduction. Examples are provided to demonstrate calculations for input power, output power, and efficiency.
Class AB amplifiers combine aspects of Class A and Class B amplifiers. They are biased so both transistors conduct for small signals like Class A for lower distortion, and for large signals only one transistor conducts at a time like Class B for higher efficiency. The circuit uses a voltage divider and diodes to bias the transistors into slight conduction even without an input signal. This overcomes crossover distortion. The output operates with the Q-point slightly above cutoff and ac cutoff at the supply voltage for Class AB operation between Class A and Class B.
Power amplifiers are concerned with efficiency, maximum power capability, and impedance matching to the output device rather than small-signal factors like amplification, linearity, and gain. There are several classes of power amplifiers including Class A, B, AB, C, and D which differ based on the conduction angle of the output and location of the Q-point. Efficiency increases as the conduction angle decreases from Class A to Class B to Class C. Transformers can be used to improve efficiency and increase the output swing of Class A amplifiers. Push-pull configurations are used for Class B amplifiers to generate a full output cycle from two transistors.
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.
in this slide you will learn what are classes of amplifiers and what is main difference between all classes of amplifier
and after reading this slide you will be able to explain all clases of amplifier
The document summarizes different classes of power amplifiers: Class A amplifiers conduct through the full 360 degrees of the input signal with the Q-point set in the middle of the load line. Class B amplifiers conduct through 180 degrees of the input with the Q-point at 0V. Class AB is a compromise between A and B, conducting between 180-360 degrees with the Q-point between the midpoint and cutoff. Class C conducts less than 180 degrees with the Q-point below cutoff. Class D is biased for digital signals and has high efficiency.
A power amplifier is designed to provide maximum power output and is used to amplify weak signals to a level sufficient to drive a loudspeaker or other output device. It consists of multiple stages, with the final stage designed specifically for high power output. Power amplifiers use power transistors that can handle large currents and dissipate significant heat. They are classified based on the operating mode of the transistors, including class A, B, AB, and C power amplifiers. Transformer coupling is commonly used to match impedances in power amplifier circuits.
1. A multistage amplifier achieves greater voltage and power gain by using multiple amplification stages connected in cascade. The overall voltage gain is equal to the product of the individual stage gains.
2. Gain is often expressed in decibels (dB) which allows both small and large quantities to be conveniently represented on a logarithmic scale corresponding to human perception. The overall multistage amplifier gain in dB is the sum of the individual stage gains in dB.
3. Common types of coupling between stages include RC coupling using capacitors, direct coupling without coupling elements, and transformer coupling. RC coupling is inexpensive but limits low frequency response while direct coupling can amplify low frequencies without coupling elements.
This document discusses power amplifiers and class A amplifiers. It begins with an introduction to power amplifiers, including their purpose of delivering high power to low resistance loads. It then covers classification of amplifiers based on conduction angle and efficiency ratings. The document analyzes class A amplifiers in detail, including derivation of input power, output power, and efficiency equations. It shows the efficiency of class A amplifiers is limited to 25% theoretically due to continuous conduction. Examples are provided to demonstrate calculations for input power, output power, and efficiency.
This document summarizes a project to simulate a class F power amplifier operating at 2.4 GHz using ADS software. The objectives were to achieve over 50% power added efficiency and output power over 30 dBm. It provides background on power amplifiers and performance parameters. It describes the simulation steps taken, including DC analysis, stability analysis, load pull analysis, and impedance matching. The simulations achieved 62% power added efficiency and 33 dBm output power. Future work and conclusions are also presented.
This document discusses the frequency response of operational amplifiers. It defines frequency response as a measure of the output spectrum of a system in response to an input stimulus over a range of frequencies. It describes how open-loop gain, frequency compensation, closed-loop gain, gain-bandwidth product, and slew rate characterize the non-ideal frequency response of op-amps. Frequency compensation modifies the gain and phase characteristics to increase bandwidth by adding resistance-capacitance networks. The gain-bandwidth product provides a measure of an op-amp's useful bandwidth.
This document discusses Class A power amplifiers. Key points:
- Class A amplifiers conduct for the entire signal cycle, resulting in the lowest efficiency. The quiescent point is in the middle of the load line.
- A series fed Class A power amplifier uses a fixed bias circuit to set the operating point. The dc bias current and voltage determine the quiescent point.
- In AC operation, an input signal causes the output to vary above and below the quiescent point. The output swings until current or voltage limits are reached.
Maximum efficiency can be calculated using the maximum possible voltage and current swings given the supply voltage and load resistance. An example problem calculates input power
This document describes a summing amplifier circuit using an operational amplifier (op-amp). The summing amplifier allows multiple input signals to be added together at the output. It discusses an inverting summing amplifier configuration with three input voltages V1, V2 and V3. The circuit produces an output voltage proportional to the algebraic sum of the three input voltages, effectively adding them, because each input sees its own resistor and they are isolated by the op-amp's virtual earth. Scaling can also be achieved if the input resistors are unequal.
Comparator circuits compare two input voltages and produce a logic output signal that is high or low depending on which input is larger. Real comparators do not have an abrupt transition and have very high voltage gain in the transition region. Comparators are often used as interfaces between analog and digital circuits by converting analog signals to logic levels. Open-collector outputs are useful for this by producing either 0V or the supply voltage at their outputs. Schmitt triggers, which are comparators with positive feedback, are commonly used as they introduce hysteresis which helps eliminate unwanted output transitions from noise.
Eeg381 electronics iii chapter 2 - feedback amplifiersFiaz Khan
This document discusses feedback amplifiers and the four basic feedback topologies:
1) Series-shunt feedback for voltage amplifiers
2) Shunt-series feedback for current amplifiers
3) Series-series feedback for transconductance amplifiers
4) Shunt-shunt feedback for transresistance amplifiers
It also covers negative feedback voltage amplifiers, including calculating closed-loop gain, gain desensitivity, and bandwidth extension due to feedback. An example problem is worked through to demonstrate these concepts.
The operational amplifier, or op-amp, is a basic building block of analog electronic circuits that amplifies the difference between its input terminals. It has very high gain, typically around 100,000, and its output depends on the difference between the voltages at its two input terminals. By using negative feedback, most of the open-loop gain is canceled out, making the op-amp useful for various applications like non-inverting and inverting amplifiers, adders, integrators, and differentiators. An ideal op-amp has infinite gain, bandwidth, and input impedance and zero output impedance. Practical op-amps have limitations compared to the ideal but can still perform signal amplification and processing functions.
This document discusses different classes of power amplifiers:
- Class A amplifiers have constant current flow and output varies over the full input cycle. Maximum efficiency is 25%.
- Class B amplifiers have current flow for only half the input cycle. They require a push-pull configuration of two transistors to generate the full output cycle. Maximum efficiency is 78.5%.
- Class AB operates between classes A and B with output between 180-360 degrees.
- Class C has output for less than half the cycle and requires a resonant load circuit. It has the highest efficiency but also the highest distortion.
Class A amplifiers have the highest linearity because the transistor is always conducting. They are the least efficient at 30% due to continuous power loss. Class B amplifiers only conduct for half of the signal cycle, improving efficiency to 50% but introducing crossover distortion. Class AB balances efficiency and distortion by conducting more than half but less than the full cycle. Class C amplifiers have the greatest efficiency of 80% but introduce heavy distortion as they conduct for less than half of the input cycle. They are used for radio frequency amplification rather than audio.
OP-AMP Configurations: Inverting and Non-InvertingAtharva Chavan
The document discusses two configurations of operational amplifiers (OP-AMPs): inverting and non-inverting. The inverting configuration uses a single resistor connected to the input and a feedback resistor, producing a 180 degree phase shift between input and output. The non-inverting configuration uses a resistor connected to ground and a feedback resistor, with the input directly applied to the non-inverting terminal and the output in phase with the input. Circuit diagrams, input/output waveforms, and voltage gain calculations are provided for both configurations.
This document discusses MOSFETs and JFETs. It introduces MOSFETs, describing the metal oxide layer and how the electric field controls current. It describes types of MOSFETs and their applications, particularly as switches. Characteristic curves of MOSFETs are also mentioned. The document then introduces JFETs, describing their structure and operation. Applications of JFETs as switches are provided. Advantages and disadvantages of JFETs are listed. Finally, characteristics curves of JFETs, including output and transfer characteristics, are described.
This document discusses power amplifiers and class A amplifiers. It describes how class A amplifiers have low efficiency since the collector current is always nonzero, even with no input signal. It then discusses transformer-coupled class A amplifiers, how they use a transformer to couple the output to the load, providing DC isolation. This increases their efficiency over standard RC-coupled class A amplifiers.
This document discusses feedback amplifiers and provides details on:
1. Feedback amplifiers can be positive or negative, with negative feedback reducing gain and improving performance. Negative feedback subtracts part of the output from the input.
2. The basic structure of a single-loop feedback amplifier feeds part of the output back to the input. This reduces gain but improves stability, bandwidth, noise, and distortion compared to a basic amplifier.
3. Amplifiers are classified based on their input and output signals as voltage, current, transconductance, or transresistance amplifiers depending on whether the input is voltage or current and the output relationship.
This document discusses tuned amplifiers, including their characteristics, classifications, and circuit types. It describes tuned amplifiers' ability to selectively amplify signals at resonant frequencies. The key circuit types discussed are single tuned, double tuned, and staggered tuned amplifiers. It also covers topics like Q-factor, series and parallel resonance, and stability considerations for tuned amplifier design. The document appears to be from an electronics course, outlining tuned amplifier concepts and circuits.
Ideal OP
AMP characteristics, DC characteristics, AC
characteristics, differential amplifier; frequency response of
OP AMP; Basic applications of op amp Inverting and Non
inverting Amplifiers, summer, differentiator and integrator
V/I & I/V converters.
1. The op-amp circuit consists of an input stage, intermediate stage, and output stage, as well as biasing circuits.
2. The input stage uses a differential amplifier configuration to provide high input impedance. The intermediate stage provides voltage gain.
3. The output stage is typically class AB to reduce crossover distortion, using a voltage source to provide constant base voltage for the transistors.
The document discusses DC and AC analysis of transistor amplifiers. It covers DC biasing circuits, voltage divider bias, graphical DC analysis using load lines and Q-point, AC equivalent circuits, and determining amplifier compliance from the AC load line. Key points are:
- DC load line shows all combinations of collector current (IC) and collector-emitter voltage (VCE) for given values of voltage and resistors.
- Q-point is the operating point where the load line intersects the transistor characteristic curve with no input signal.
- AC load line determines maximum output voltage compliance or swing based on saturation and cutoff points.
Here are the steps to solve this:
1) VZ = VBE3 (zener voltage is equal to BJT base-emitter voltage)
2) Using KVL: -VZ + VBE3 + IE3RE = 0
3) Simplify: IE3RE = 0
4) IE3 is constant
Therefore, with a zener diode replacing R2, the current IE3 (and thus IT) remains constant regardless of load or temperature variations. The zener diode acts to stabilize the BJT base-emitter voltage, keeping the current constant.
This document provides an overview of different classes of electronic amplifiers (A, AB, B, C, D, E, F, G, H) and their characteristics. Class A amplifiers have the highest sound quality but are the least efficient, as the output transistors conduct electricity for the entire input cycle. Class AB amplifiers are more efficient than Class A as they only conduct for more than half the cycle. Class B amplifiers use two output devices in a push-pull configuration to generate the full output cycle. Class D and E amplifiers are highly efficient switching amplifier designs. The document also discusses field effect transistors and includes circuit diagrams to illustrate the different classes.
power amplifier -IT IS ONE OF THE AMPLIFIER WHICH CAN HANDLE LARGER SIGNALSAbinaya Saraswathy T
This document discusses different types of power amplifiers:
- Class A amplifiers conduct over the full 360 degrees of the input signal cycle and have the Q-point set in the middle of the load line, providing low distortion but low efficiency of around 25%. Transformer coupling can improve efficiency to 50%.
- Class B amplifiers conduct over 180 degrees with the Q-point at cutoff, improving efficiency but introducing crossover distortion if not implemented as a push-pull circuit.
- Class AB is a compromise between A and B, conducting between 180-360 degrees. Class C amplifiers conduct less than 180 degrees and require an LC tank circuit to generate a full sine wave output.
This document summarizes a project to simulate a class F power amplifier operating at 2.4 GHz using ADS software. The objectives were to achieve over 50% power added efficiency and output power over 30 dBm. It provides background on power amplifiers and performance parameters. It describes the simulation steps taken, including DC analysis, stability analysis, load pull analysis, and impedance matching. The simulations achieved 62% power added efficiency and 33 dBm output power. Future work and conclusions are also presented.
This document discusses the frequency response of operational amplifiers. It defines frequency response as a measure of the output spectrum of a system in response to an input stimulus over a range of frequencies. It describes how open-loop gain, frequency compensation, closed-loop gain, gain-bandwidth product, and slew rate characterize the non-ideal frequency response of op-amps. Frequency compensation modifies the gain and phase characteristics to increase bandwidth by adding resistance-capacitance networks. The gain-bandwidth product provides a measure of an op-amp's useful bandwidth.
This document discusses Class A power amplifiers. Key points:
- Class A amplifiers conduct for the entire signal cycle, resulting in the lowest efficiency. The quiescent point is in the middle of the load line.
- A series fed Class A power amplifier uses a fixed bias circuit to set the operating point. The dc bias current and voltage determine the quiescent point.
- In AC operation, an input signal causes the output to vary above and below the quiescent point. The output swings until current or voltage limits are reached.
Maximum efficiency can be calculated using the maximum possible voltage and current swings given the supply voltage and load resistance. An example problem calculates input power
This document describes a summing amplifier circuit using an operational amplifier (op-amp). The summing amplifier allows multiple input signals to be added together at the output. It discusses an inverting summing amplifier configuration with three input voltages V1, V2 and V3. The circuit produces an output voltage proportional to the algebraic sum of the three input voltages, effectively adding them, because each input sees its own resistor and they are isolated by the op-amp's virtual earth. Scaling can also be achieved if the input resistors are unequal.
Comparator circuits compare two input voltages and produce a logic output signal that is high or low depending on which input is larger. Real comparators do not have an abrupt transition and have very high voltage gain in the transition region. Comparators are often used as interfaces between analog and digital circuits by converting analog signals to logic levels. Open-collector outputs are useful for this by producing either 0V or the supply voltage at their outputs. Schmitt triggers, which are comparators with positive feedback, are commonly used as they introduce hysteresis which helps eliminate unwanted output transitions from noise.
Eeg381 electronics iii chapter 2 - feedback amplifiersFiaz Khan
This document discusses feedback amplifiers and the four basic feedback topologies:
1) Series-shunt feedback for voltage amplifiers
2) Shunt-series feedback for current amplifiers
3) Series-series feedback for transconductance amplifiers
4) Shunt-shunt feedback for transresistance amplifiers
It also covers negative feedback voltage amplifiers, including calculating closed-loop gain, gain desensitivity, and bandwidth extension due to feedback. An example problem is worked through to demonstrate these concepts.
The operational amplifier, or op-amp, is a basic building block of analog electronic circuits that amplifies the difference between its input terminals. It has very high gain, typically around 100,000, and its output depends on the difference between the voltages at its two input terminals. By using negative feedback, most of the open-loop gain is canceled out, making the op-amp useful for various applications like non-inverting and inverting amplifiers, adders, integrators, and differentiators. An ideal op-amp has infinite gain, bandwidth, and input impedance and zero output impedance. Practical op-amps have limitations compared to the ideal but can still perform signal amplification and processing functions.
This document discusses different classes of power amplifiers:
- Class A amplifiers have constant current flow and output varies over the full input cycle. Maximum efficiency is 25%.
- Class B amplifiers have current flow for only half the input cycle. They require a push-pull configuration of two transistors to generate the full output cycle. Maximum efficiency is 78.5%.
- Class AB operates between classes A and B with output between 180-360 degrees.
- Class C has output for less than half the cycle and requires a resonant load circuit. It has the highest efficiency but also the highest distortion.
Class A amplifiers have the highest linearity because the transistor is always conducting. They are the least efficient at 30% due to continuous power loss. Class B amplifiers only conduct for half of the signal cycle, improving efficiency to 50% but introducing crossover distortion. Class AB balances efficiency and distortion by conducting more than half but less than the full cycle. Class C amplifiers have the greatest efficiency of 80% but introduce heavy distortion as they conduct for less than half of the input cycle. They are used for radio frequency amplification rather than audio.
OP-AMP Configurations: Inverting and Non-InvertingAtharva Chavan
The document discusses two configurations of operational amplifiers (OP-AMPs): inverting and non-inverting. The inverting configuration uses a single resistor connected to the input and a feedback resistor, producing a 180 degree phase shift between input and output. The non-inverting configuration uses a resistor connected to ground and a feedback resistor, with the input directly applied to the non-inverting terminal and the output in phase with the input. Circuit diagrams, input/output waveforms, and voltage gain calculations are provided for both configurations.
This document discusses MOSFETs and JFETs. It introduces MOSFETs, describing the metal oxide layer and how the electric field controls current. It describes types of MOSFETs and their applications, particularly as switches. Characteristic curves of MOSFETs are also mentioned. The document then introduces JFETs, describing their structure and operation. Applications of JFETs as switches are provided. Advantages and disadvantages of JFETs are listed. Finally, characteristics curves of JFETs, including output and transfer characteristics, are described.
This document discusses power amplifiers and class A amplifiers. It describes how class A amplifiers have low efficiency since the collector current is always nonzero, even with no input signal. It then discusses transformer-coupled class A amplifiers, how they use a transformer to couple the output to the load, providing DC isolation. This increases their efficiency over standard RC-coupled class A amplifiers.
This document discusses feedback amplifiers and provides details on:
1. Feedback amplifiers can be positive or negative, with negative feedback reducing gain and improving performance. Negative feedback subtracts part of the output from the input.
2. The basic structure of a single-loop feedback amplifier feeds part of the output back to the input. This reduces gain but improves stability, bandwidth, noise, and distortion compared to a basic amplifier.
3. Amplifiers are classified based on their input and output signals as voltage, current, transconductance, or transresistance amplifiers depending on whether the input is voltage or current and the output relationship.
This document discusses tuned amplifiers, including their characteristics, classifications, and circuit types. It describes tuned amplifiers' ability to selectively amplify signals at resonant frequencies. The key circuit types discussed are single tuned, double tuned, and staggered tuned amplifiers. It also covers topics like Q-factor, series and parallel resonance, and stability considerations for tuned amplifier design. The document appears to be from an electronics course, outlining tuned amplifier concepts and circuits.
Ideal OP
AMP characteristics, DC characteristics, AC
characteristics, differential amplifier; frequency response of
OP AMP; Basic applications of op amp Inverting and Non
inverting Amplifiers, summer, differentiator and integrator
V/I & I/V converters.
1. The op-amp circuit consists of an input stage, intermediate stage, and output stage, as well as biasing circuits.
2. The input stage uses a differential amplifier configuration to provide high input impedance. The intermediate stage provides voltage gain.
3. The output stage is typically class AB to reduce crossover distortion, using a voltage source to provide constant base voltage for the transistors.
The document discusses DC and AC analysis of transistor amplifiers. It covers DC biasing circuits, voltage divider bias, graphical DC analysis using load lines and Q-point, AC equivalent circuits, and determining amplifier compliance from the AC load line. Key points are:
- DC load line shows all combinations of collector current (IC) and collector-emitter voltage (VCE) for given values of voltage and resistors.
- Q-point is the operating point where the load line intersects the transistor characteristic curve with no input signal.
- AC load line determines maximum output voltage compliance or swing based on saturation and cutoff points.
Here are the steps to solve this:
1) VZ = VBE3 (zener voltage is equal to BJT base-emitter voltage)
2) Using KVL: -VZ + VBE3 + IE3RE = 0
3) Simplify: IE3RE = 0
4) IE3 is constant
Therefore, with a zener diode replacing R2, the current IE3 (and thus IT) remains constant regardless of load or temperature variations. The zener diode acts to stabilize the BJT base-emitter voltage, keeping the current constant.
This document provides an overview of different classes of electronic amplifiers (A, AB, B, C, D, E, F, G, H) and their characteristics. Class A amplifiers have the highest sound quality but are the least efficient, as the output transistors conduct electricity for the entire input cycle. Class AB amplifiers are more efficient than Class A as they only conduct for more than half the cycle. Class B amplifiers use two output devices in a push-pull configuration to generate the full output cycle. Class D and E amplifiers are highly efficient switching amplifier designs. The document also discusses field effect transistors and includes circuit diagrams to illustrate the different classes.
power amplifier -IT IS ONE OF THE AMPLIFIER WHICH CAN HANDLE LARGER SIGNALSAbinaya Saraswathy T
This document discusses different types of power amplifiers:
- Class A amplifiers conduct over the full 360 degrees of the input signal cycle and have the Q-point set in the middle of the load line, providing low distortion but low efficiency of around 25%. Transformer coupling can improve efficiency to 50%.
- Class B amplifiers conduct over 180 degrees with the Q-point at cutoff, improving efficiency but introducing crossover distortion if not implemented as a push-pull circuit.
- Class AB is a compromise between A and B, conducting between 180-360 degrees. Class C amplifiers conduct less than 180 degrees and require an LC tank circuit to generate a full sine wave output.
1. Amplifiers are classified according to frequency capabilities, coupling methods, and use. They can be audio frequency amplifiers, radio frequency amplifiers, voltage amplifiers, or power amplifiers.
2. Voltage amplifiers aim to amplify input voltage with minimal current output, while power amplifiers amplify input power with minimal voltage change. Power amplifiers are needed for applications requiring high power loads.
3. Amplifiers also have different classes based on their operating point, including class A operated linearly over the entire cycle, and classes B and AB operated over more than 180 degrees but with higher efficiency. Class C amplifiers are used in radio frequency applications as they operate for less than 180 degrees with even
This document discusses different classifications of amplifiers:
1. According to frequency capabilities (audio vs. radio frequency amplifiers).
2. According to coupling methods (RC, transformer, direct coupled).
3. According to use (voltage amplifiers aim to amplify voltage with minimal current output, while power amplifiers aim to amplify power with minimal voltage change output).
It also discusses different classes of amplifiers based on their biasing point: Class A are biased in the linear region all the time, Class B are biased at cutoff so conduct for 180 degrees, Class AB are biased slightly above cutoff to conduct more than 180 degrees, and Class C are biased to conduct for much less than 180 degrees.
The document discusses different types of power amplifiers and their output stages. It begins by defining a power amplifier as a large signal amplifier that is generally the last stage of a multistage amplifier. Its purpose is to amplify a weak signal to a level that can operate an output device like a loudspeaker. The document then discusses different classes of output stages - Class A, B, C - based on the collector current waveform. It also covers topics like efficiency, distortion, and AC/DC load lines of power amplifiers.
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.
A voltage amplifier circuit is a circuit that amplifies the input voltage to a higher voltage. So, for example, if we input 1V into the circuit, we can get 10V as output if we set the circuit for a gain of 10. Voltage amplifiers, many times, are built with op amp circuits.
This document discusses different classes of power amplifiers, including class A, class B, class AB, and push-pull amplifiers. It provides details on the operating principles, biasing, power efficiency, and output characteristics of each type. Key points include: Class A amplifiers have output current flowing for the full input cycle, leading to low efficiency. Class B amplifiers only conduct for half the input cycle. Class AB provides a small amount of bias to increase conduction. Push-pull amplifiers use two transistors connected out of phase to increase power and gain.
This document discusses class C amplifiers. It defines an amplifier as an electronic device that increases the voltage, current, or power of a signal. It then explains that a class C amplifier is a type of amplifier where the active element (transistor) conducts for less than half of the input signal cycle, resulting in high efficiency but high distortion. The document provides a diagram of a class C amplifier circuit and explains its components and operation. It notes that class C amplifiers are commonly used in radio frequency applications due to their high efficiency.
This document provides an introduction to signal amplifiers. It discusses different types of amplifiers including operational amplifiers, small signal amplifiers, and power amplifiers. It describes the key properties of amplifiers including input resistance, output resistance, and gain. It also discusses amplifier gain in terms of voltage gain, current gain, and power gain. Different classes of amplifier operation are covered, including classes A, B, AB, and their characteristics. Biasing techniques and their role in establishing the operating point of amplifiers is also explained.
Power amplifiers are classified based on their operating point or quiescent point (Q point). Class A amplifiers have their Q point at the center of the load line, resulting in linear but low efficiency operation. Class B amplifiers operate with their Q point at cutoff, providing high efficiency but distorted output. Class AB reduces distortion by adding some forward bias. Class D amplifiers switch between cutoff and saturation at a high frequency for very high efficiency operation suitable for audio.
This document provides information about different classes of amplifiers, including Class A, Class B, Class AB, and transformer-coupled amplifiers. It discusses the key characteristics of each type of amplifier, such as conduction angle, efficiency, and whether they use a single transistor or complementary pair. The Class A amplifier has a conduction angle of 360 degrees but low efficiency. Class B amplifiers have a conduction angle of 180 degrees and higher efficiency of around 70% but can experience crossover distortion without additional biasing. Class AB amplifiers add small bias voltages to eliminate crossover distortion while maintaining higher efficiency than Class A.
This document discusses the characteristics and applications of operational amplifiers (op-amps). It begins with a block diagram showing the typical components of an op-amp, including the differential amplifier stage, intermediate stage, level shifting stage, and output stage. It then covers ideal and practical characteristics of op-amps such as high input impedance, low output impedance, high voltage gain, and finite bandwidth. Common op-amp configurations like the inverting and non-inverting amplifiers are explained. The document provides detailed descriptions and circuit diagrams to illustrate op-amp characteristics and applications.
- Class A amplifiers have high voltage gain but low efficiency, as the output transistor constantly conducts current even without an input signal.
- Class B amplifiers improve efficiency by using two transistors in a push-pull configuration, but suffer from crossover distortion as both transistors are briefly off at the same time during signal transitions.
- Class AB amplifiers reduce crossover distortion by applying a small bias voltage, so the transistors conduct slightly more than half of each cycle and efficiency is improved over Class A while minimizing distortion.
After audio signals are converted to electrical signals, they undergo several stages of voltage amplification before final power amplification by a power amplifier just before the speaker. A power amplifier both raises the power level of the input signal and converts DC power to AC power controlled by the input signal. The main difference between a voltage amplifier and power amplifier is that a voltage amplifier aims to maximize voltage gain while a power amplifier aims to maximize power output. Power amplifiers are further classified by frequency range handled (audio or radio frequency) and by their operating mode (Class A amplifies over the full cycle, Class B over the positive half, etc).
Electrical current, voltage, resistance, capacitance, and inductance are a few of the basic elements of electronics and radio. Apart from current, voltage, resistance, capacitance, and inductance, there are many other interesting elements to electronic technology. ... Use Electronics Notes to learn electronics online.
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Introduction
Band Pass Amplifiers
Series & Parallel Resonant Circuits & their Bandwidth
Analysis of Single Tuned Amplifiers
Analysis of Double Tuned Amplifiers
Primary & Secondary Tuned Amplifiers with BJT & FET
Merits and de-merits of Tuned Amplifiers
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2. CONTENTS:-
Power Amplifier circuits.
Output stages of types of power amplifier (class A,
class B, class AB, class C, class D)
Distortions( Harmonic and Crossover).
Push-pull amplifier with and without transformer.
Complimentary symmetry and Quasi-
complimentary symmetry push pull amplifier.
3. POWER AMPLIFIERS:-
Power Amplifier is a circuit which draw power from
D.C. power source and convert into A.C. power and
whose action is controlled by input signal. Power
Amplifier needs large current ,So they are known as
large signal amplifier. In other words we can say that
it is a multistage amplifier which consists a number of
stages that amplify a weak signal until sufficient
power available to operate a speaker or other power
handling devices.
4. POWER AMPLIFIERS:-
In power amplifier transformer primary winding is in
series with collector. DC power loss in primary
winding is very less as its resistance is small. Power
transfer to the secondary winding is A.C.
The initial stages which are basically voltage
amplifiers , amplify the voltage level of signal. The
last stage is called power stage and uses a power
amplifiers to amplify the power level of signal.
6. POWER TRANSISTOR:-
The transistor which is employed in power amplifier
is called power transistor. It is different from other
transistors in the following manner :
Base terminal is thicker to reduce the value of
current amplification factor.
Emitter and base layer are heavily doped.
Area of collector region is made large in order to
dissipate the heat developed in transistor during
operation.
7. TERMS USED IN POWER AMPLIFIER:-
COLLECTOR EFFICIENCY(CONVERSION
EFFICIENCY):-
The effectiveness of power amplifier is measured on the
basis of its ability to convert dc power into ac power.
Power amplifier are designed to provide maximum
collector efficiency.
The ratio of AC output power to DC power supplied by
the DC battery of power amplifier is called Collector
Efficiency.
Collector efficiency=A.C power/D.C. power
8. The ratio of AC output power to DC power
supplied by the DC battery of power
amplifier is termed as collector efficiency.
%collector efficiency=AC power delivered
to load/DC power supplied to load
=(Pac/Pdc)100
9. DISTORTION:-
Characteristics of power transistor is very non-linear.
Due to this non-linearity the wave shape of output
signal becomes different from waveform of input
signal.
Distortion is defined as the change of output wave
shape from the input wave shape of the amplifier.
10. POWER DISSIPATION CAPACITY
(COLLECTOR DISSIPATION):-
To keep the temperature within limit the transistor
must dissipate this heat to its surroundings. For this
Heat Sink is attached.
The ability of transistor to dissipate heat developed
in it is called as power dissipation capacity.
11. COMPARISION OF VOLTAGECOMPARISION OF VOLTAGE
AMPLIFIER AND POWER AMPLIFIER:-AMPLIFIER AND POWER AMPLIFIER:-
Difference between them is as follow:-
12. S.NO Voltage
amplifier
Power
amplifier
1 Transistor chosen should have high
value of β about 100
Transistor should have small value of
β about 20 to 50.
2 Load resistance Rc has high value
about 10KΩ
Load has small value 10Ω to 20Ω
3 Input voltage is low approx few mV Input voltage is high about few volt
4 It has low power output & high
voltage output.
It has high power output and low
voltage output .
5 Collector current has low value
100mA.
Collector current has high value.
6 Output impedance of voltage
amplifier has high value.
Output impedance has low value.
7 Usually R-C coupling is used. Transformer or tuned circuit is always
used
13. CLASSIFICATION OF POWER
AMPLIFIER:-
Power amplifier
Primary
class
according to
freq.)
According to mode of
operation
Based on driving output
Audio amp.
Radio amp.
Class A
Class B
Class AB
Class C
Class D
Single ended P.A.
Double ended P.A.
Push-Pull P.A.
Complementary &
Symmetry Push
Pull P.A.
Quasi Symmetry
Push Pull PA
14. AUDIO POWER AMPLIFIER:-
It is small signal power amplifier which is
used to raise power level of audio frequency
range(20Hz-20KHz).
15. RADIO POWER AMPLIFIER:-
It is large signal power amplifiers raise
the power level of signals that have radio
frequency range from 20kHz to several MHz.
16. CLASS-A POWER AMPLIFIER:-
In this case transistor is so biased that output
current flows for the entire cycle (for 360 degree) of
the input signal thus the output wave is exactly same
as the input wave.
It’s collector efficiency is for-
(a) Direct coupling-25%
(b) Transformer coupling-50%
17. In this case the transistor bias and signal amplitude
are such that output current flows only during
positive half cycle(180 degree) of the input signal.
Output from Class-B operation is a rectified half
wave. Such a amplifiers are mostly used in Push-
Pull arrangements.
It’s collector efficiency is 78.5%.
CLASS-B POWER AMPLIFIER:-
18. CLASS-AB POWER AMPLIFIER:-
The characteristics of Class-AB amplifier lies
between Class-A and Class-B amplifiers.
It is so biased that it works for complete
positive half cycle and half of the negative
cycle.
Total conduction period is less than 360 degree but
more than 180 degree. Output signal obtained in
Class-AB operation is distorted.
19. CLASS C POWER AMPLIFIER:-
A class C power amplifier is biased for operation for
less than 180 degree of the input signal cycle and
will operate only with a tuned or resonant circuit. In
its operation the output current flow for less than one
half cycle.
Collector efficiency of class C amplifier is 85-90%.
It is used in Tuned circuits for the purpose of Radio
or communication in RF range.
20. CLASS D POWER AMPLIFIER:-
A Class D power amplifiers are designed to operate
with digital or pulse type signals and it’s overall
efficiency above 90 degree.
MOSFET is mainly used in Class-D amplifiers.
The efficiency of class D amplifier is above 90%.
21. SINGLE ENDED POWER AMPLIFIER:-
It uses single transistor and derives output power
with one end permanently ground.
22. DOUBLE ENDED POWER AMPLIFIER:-
Double ended uses two transistors in single stage. It
consists of two loops in which the transistor
collector current flows in opposite direction but add
in the load.
23. PUSH PULL POWER AMPLIFIER:-
It uses two transistors having
complementary symmetry (one PNP and
NPN). They have symmetry as they are
made with the same material and technology.
24. COMPLEMENTRAY & SYMMETRY
POWER AMPLIFIER
This is nothing but a Push Pull amplifier in which we
use a phase-splitter circuit to make phase shift of
180`
25. QUASI SYMMETRY POWER AMPLIFIER
This is amplifier in which we use four transistor of
two group as:
Group 1: Darlington pair ; Q1(NPN),Q3(NPN)
Group 2: Feedback pair ; Q2(PNP),Q3(NPN)
26. CLASS-A AMPLIFIER:-
In this type, the transistor is so biased that the output
current flows for the full cycle of the input signal, as
shown in fig.
This means that the transistor remains forward biased
throughout the input cycle. From fig. it is seen that the
operating point Q is located at the centre of the load
line. So that the output current flows for complete
cycle of the input signal.
28. Class A power amplifier:-
INPUT
WAVEFORM
OUTPUT
WAVEFORM
29. CLASS-A AMPLIFIER:-
In class A operation, signal is faithfully reproduced at
the output without any distortion. This is an important
feature of class A operation. The efficiency of class-A
operation is very small.
As the collector current flows for 360degree (full cycle)
of the input signal. We can say that the angle of the
collector current flow is 360degree.
30. CLASS-A AMPLIFIER:-
DRAWING LOAD LINES :-
When the base current Ib is zero, the collector current Ic
is also equal to zero (neglecting reverse saturation
current Ico).
Therefore the voltage drop across load resistance is
also equal to zero and hence the collector-emitter
voltage Vce becomes equal to Vcc. Thus we get the
point 1 on fig which represents the condition of Ic =0
and Vce=Vcc.
31. CLASS-A AMPLIFIER:-
The Q point:-
For or class-A power amplifier, it is necessary that
transistor should conduct for the full 360 degree of
the input cycle.
Thus Q point (or operating point) selected
approximately is the mid of load line. It is shown in
the fig. as Q, here Icq represents zero signal
collector current and Vcq represents zero signal
voltage between collector and emitter respectively.
32. CLASS-A AMPLIFIER:-
operation :-
Let us assume that the input signal to the amplifier
to the amplifier is sinusoidal which results in a
sinusoidal variation of base current Ib. this in turn will
cause the collector current Ic and collector-emitter
voltage Vce to vary sinusoidally around the Q point.
33. CLASS-A AMPLIFIER:-
D.C. power input:-
The D.C. power input is provided by the supply Vcc
And with no input signal, the d.c. current drawn is
the collector bias current Icq. Hence d.c. power input
is
Pdc = Vcc.Icq
34. CLASS-A AMPLIFIER:-
A.C. power input:-
Let the peak value of collector current swing be
and that of collector voltage swing be
Vm.Hence there r.m.s. values are :
Im / √2 and Vm / √2
A.C. Power output using R.M.S. values :-
The a.c. power output is given by
Pac = Vrms Irms
= I2
rms RL
= V2
rms/RL
35. CLASS-A AMPLIFIER:-
A.C. Power output using maximum values :-
The a.c. power output is given by :
Pac = Vrms.Irms
=(Vm/√2).Im/√2
=(Vm Im)/2
Since Im = Vm / RL the above equation can be rewritten :
Pac = V2
m/2RL ----------(1)
Pac = I2
mRL / 2 ----------(2)
Equation (1)and(2) represents a.c. power output using
peak
values.
36. ANALYSIS OF CLASS-A AMPLIFIERS:-
The class –A amplifiers are further classified as :
(1) Series fed directly coupled class-A amplifiers
(2) Transformer coupled class–A amplifiers
37. SERIES FED DIRECTLY COUPLED
AMPLIFIER:-
In directly coupled type, the load is connected
directly in the collector. While in the transformer-
coupled type, the load is coupled to the collector
through a transformer.
40. AC OPERATION OF SERIES
CLASS A AMPLIFIER:-
o/p current
swing
o/p voltage swing
i/p signal
Ic
Vcc/Rc
Vcc Vce0
41. ANALYSIS OF SERIES FED DIRECT
COUPLED CLASS A AMPLIFIERS:-
The diagram shows a class of series fed amplifier. It
is so named because the load resistance RL is
connected directly in series with collector of the
transistor Q. Resistor R1,R2,Re and capacitor Ce
are used for biasing.
To understand the operation of the circuit, we take
help of graphical method.
42. A.C. POWER OUTPUT USING PEAK TO
PEAK VALUES:-
wt
Imax
0
Imin
π/2 π
1
2
3
D.C. bias value
ic
43. A.C. POWER OUTPUT USING PEAK TO PEAK
VALUES:-
We have from Equation
Pac = Vm Im/2
but as Vm = Vpp/2 = (Vmax-Vmin)/2
Also Im = Ipp/2 = (Vmax-Vmin)/2
We get Pac = (Vpp/2.Ipp/2)/2 = Vpp.Ipp/8
= (Vmax–Vmin)(Imax-Imin)/8
44. EFFICIENCY:-
The efficiency of an amplifier represents the a.c.
power delivered to the load from the d.c. source. The
generalized expression for efficiency of an amplifier is
given as
%η = Pac/Pdc *100
%η = ( Vmax-Vmin) (Imax- Imin)/8VccIcq*100
This efficiency is also called as conversion efficiency of
an amplifier.
45. MAXIMUM EFFICIENCY:-
From dig. we can say that minimum voltage possible
is zero and maximum voltage possible is Vcc, for a
maximum swing. Similarly the minimum current is
zero and the maximum current possible is 2Icq, for a
maximum swing i.e.
Vmax = Vcc and Vmin = 0
Imax = 2Icq and Imin =0
% η = (Vcc-0)(2Icq-0)/8Vcc.I cq.100
= (2VccIcq/8VccIcq).100 = 25%
46. This the maximum efficiency possible in directly
coupled series fed class-A amplifier is just 25%
(ideally). In practical it is less than 25%.
47. POWER DISSIPATION:-
The amount of power that must be dissipated by the
transistor is the difference between the d.c. power
input Pdc and the a.c. power delivered to the load
Pac.
Power dissipation
Pd = Pdc – Pac
Maximum power dissipation occurs when there is
zero a.c. input signal, the a.c. power output (Pac) is
also zero.
Pac = 0 because (Iac=0)
49. ADVANTAGES:-
1. The circuit is simpler to design and
to implement.
2. The load is directly connected in the collector circuit
hence no output transformer is required.
3. It keeps DC power loss small because of small
resistance of primary winding of transformer.
4. It matching of load impedance with source
impedance is possible with transformer.
50. DISADVANTAGE:-
1.The load resistance is directly connected in the
collector, therefore the quiescent collector current
flows through it, there will be considerable power
loss in the load resistance.
2. Power dissipation is more, hence use of heat sink is
essential.
51. TRANSFORMER COUPLED CLASS-A
AMPLIFIER:-
The above mentioned disadvantages of series fed
directly connected amplifier can be overcome can
be overcome by employing a transformer known as
output transformer.
The transformer is used to couple the load RL to the
collector circuit of the transistor.
53. TRANSFORMER COUPLED CLASS-A
AMPLIFIER:-
(A)CIRCUIT DIAGRAM:-
The basic circuit of a transformer-coupled amplifier
is shown in fig. the primary of the transformer,
having negligible d.c. resistance is connected in
the collector circuit. The secondary of transformer
is connected to load RL (loud speaker as load ).
54. TRANSFORMER COUPLED CLASS-A
AMPLIFIER:-
Let us consider only the transformer and the load RL
as shown in fig.
Impedance RL is connected across transformer
secondary. This impedance is changed by the
transformer when viewed at the primary side(RL).
The current ratio between primary and secondary of
the transformer be N. Therefore, the voltage ratio
and current ratio can written as
V1/V2 = N
and I2/I1 = N
55. TRANSFORMER COUPLED CLASS-A
AMPLIFIER:-
Where
N is equal to N1/N2
RL is actual load resistance
RL’ is equal to resistance presented by the
primary winding to the supply source.
The primary winding acts as a resistance equal to
load resistance across the secondary multiplied by
the square of turn ratio.
56. TRANSFORMER COUPLED CLASS-A
AMPLIFIER:-
D.C. OPERATION:-
There will be no voltage drop across the primary
winding of a transformer under quiescent condition.
The slop of d.c. load line is given as reciprocal of the
d.c. resistance in the collector circuit. The d.c.
resistance is zero hence slop will be infinite.
57. AC AND DC LOAD LINE OF TRANSFORMER
COUPLED CLASS A AMPLIFIER:-
Ic
Vce
Ac load line
Dc load line
Q
Ic max
2 Icq
Ic min=0
Vce min=0
Vce max=0
2Vcc
Icq
Vceq=Vcc
At center of ac
load line
58. TRANSFORMER COUPLED CLASS-A
AMPLIFIER:-
D.C. POWER INPUT:-
The d.c. power input is given by
Pdc=VccIcq
This expression is same as for series fed directly
coupled class-A amplifier.
59. TRANSFORMER COUPLED CLASS-A
AMPLIFIER:-
AC OPERATION:-
In class-A operation, the Q-point is located at the
center of the load line.The a.c. load line is obtained
by drawing the line throw the operating point. Slope
of a.c. load line is equal to : -1/RL
When a.c. signal is applied collector current is varies
with input signal and accordingly operating point Q
is shifted its position up and down to the load line.
60. TRANSFORMER COUPLED CLASS-A
AMPLIFIER:-
AC OUTPUT POWER:-
Generalized expression for a.c. output power for
transformer coupled amplifier is same as
Pac = (Vpp/2.Ipp/2)/2 = Vpp.Ipp/8
= (Vmax –Vmin)(Imax-Imin)/8
EFFICIENCY:-
%η = Pac/Pdc .100
%η = (Vmax-Vmin) (Imax- Imin)/8VccIcq.100
62. TRANSFORMER COUPLED CLASS-A
AMPLIFIER:-
POWER DISSIPATION:-
The power dissipation by the transistor is given
by : Pd=Pdc-Pac
When there is no input signal the entire d.c.
power gets dissipation in the form of heat, which is
maximum power dissipation.
(Pd)max=VccIcq
63. TRANSFORMER COUPLED CLASS-A
AMPLIFIER:-
Advantages:-
1 Efficiency of the operation is higher (50%)then
directly coupled series fed amplifier(25%).
2 The d.c. power bias current that flows through RL in
series fed amplifier and causes power loss in RL, is
stopped n case of transformer coupled. This is the
main reason for the increased efficiency over
series fed operation.
3 Impedance matching which is an essential
requirement for maximum power transfer is
possible.
64. DISADVANTAGES:-
1. Due to transformer the circuit becomes bulkier
and costlier.
2. The circuit is complicated to design and
implement as compared to directly coupled series
fed amplifier.
3. Frequency response of the circuit is poor.
65. HARMONIC DISTORTION IN POWER
AMPLIFIER:-
Harmonic distortion means the presence of frequency
components in the output waveform which are not
present in the input signal.
Due to non linearity amplification of all the portion
of positive and negative half cycles is not same and it
causes the output waveform to be different from
input waveform.
When the input signal is applied to a transistor the
non-linear characteristics causes the positive half of
the signal to be amplified more than negative half
cycle.
66. HARMONIC DISTORTION IN
POWER AMPLIFIER:-
Due to this output signal signal contains
fundamental frequency components and some
undesired frequency components,which are integral
multiple of input signal frequency.
These additional frequency components are called
harmonics. Hence the output is said to be distorted,
this is called harmonic distortion.
67. HARMONIC DISTORTION IN
POWER AMPLIFIER:-
Out of all the harmonic components, the second
harmonics has the largest amplitude. As the order of
the harmonic increases. Since the second harmonic
amplitude is largest, the second harmonic distortion
is more important in the analysis of Audio Frequency
amplifier.
68. HARMONIC DISTORTION IN POWER AMPLIFIER:-
Distorted sinusoidal waveform
Fundamental sinusoidal waveform
Second harmonic component
Third harmonic component
V V
V
V
V
0
0
0
0
0
Vm sin2wt
Vmcos2wt Vm sin3wt
Waveform due to
fundamental,2nd
,3rd
,harmonic
component
Vmsinwt
wt
wt
wt
wt
wt
Vm cos2wt
Vm sin2wtVm sin3wt
Vmsinwt
70. SECOND HARMONIC DISTORTION:-
For linear amplification, the dynamic transfer
characteristics relation b/w Ib
and Ic
which is known
as transfer characteristic must be linear. To evaluate
the second harmonic distortion assume that the
dynamic transfer characteristics of the transistor is
parabolic (non-linear ) in nature rather than (linear).
71. SECOND HARMONIC DISTORTION:-
Equation that describes distorted signal waveform is:
ic= ICQ
+ I0 + I1cos(ωt) + I2cos(2ωt)
Where
(ICQ+I0) =dc component independent of time.
I1= fundamental component of distorted ac signal. I2=
second harmonic component , at twice the fundamental
frequency.
72. MEASUREMENT OF SECOND HARMONIC
DISTORTION:-
At point 1,ωt=0
Ic
=ICQ
+I0
+I1cos0+I2cos0
Ic
=ICQ+I0+I1+I2 =IC(MAX)
At point 2,wt=Π/2
IC
=ICQ+I0+I1cosΠ/2+I2cos2Π/2
Ic=ICQ+I0 +I2
At point 3,wt=Π
Ic
=ICQ
+I0+I1cosΠ+I2cos2Π
Ic
=ICQ+I0-I1+I2 =IC(MIN)
73. MEASUREMENT OF SECOND
HARMONIC DISTORTION:-
At ωt=0,Ic=Imax
At ωt=Π/2,Ic=ICQ
At ωt=Π,Ic=Imin
Imax=ICQ+I0+I1+I2
Icq=ICQ+I0-I2
Imin=ICQ+I0-I1+I2,
I0=I2
Imax-Imin=2I1
74. MEASUREMENT OF SECOND HARMONIC
DISTORTION:-
I1 =(Ic max-Ic min)/2
I0 =I2
Imax+Imin=2ICQ+2(I0+I2)=2ICQ+4I2
I2=(Imax+Imin-2ICQ)/4
As the amplitude of the fundamental and second
harmonic are known ,the % of second harmonic
distortion can be calculated as
%D2=[ (I2/ I1)*100 ]
76. 5 POINT METHOD OF HARMONIC
DISTORTION:-
1. Fundamental 2,3,4,-----------so on ,harmonic
distortion is given by
D2=I2/I1
D3=I3/I1
D4 =I4/I1
and so on.
2. Total harmonic distortion is given by
D2
= D2
2
+D3
2
+D4
2
+---------
77. Measurement Of overall Harmonic
Distortion:-
3. When the distortion is negligible ,the power
delivered to the load given by
Pac=I2
mRL/2
Where
Im=peak value of the output waveform
=(Imax-Imin)/2
4. If B1=Fundamental frequency component
Pac =I2
1RL/2
78. MEASUREMENT OF OVERALL HARMONIC
DISTORTION:-
5) With distortion ,the power delivered to the load
increases proportional to the amplitude of the
harmonic component as:
(Pac )D=I2
1RL/2+I2
2RL/2
=I2
1RL(1+I2
2/I2
1)/2
=Pac(1+D2
2)
This is the power delivered to the load due the
second harmonic distortion.
79. HIGHER ORDER HARMONIC DISTORTION:-
The collector current due to higher order harmonic
be :
Ic=G1Ib+G2Ib
2
+G3Ib
3
+……….
The input signal is given by :
Ib
= Ibm
cosωt
Ic
=G1Ibmcosωt+G2Ibmcos2
ωt+G3Ibmcos3ωt+……….
Ic
=B0+B1cosωt+B2cos2ωt+B3cos3ωt+………
80. HIGHER ORDER HARMONIC DISTORTION:-
At point 1, ωt=0,Ic=Imax
Imax
=ICQ+B0+B1+B2+B3+…….
At point 2, ωt=Π/3,Ic=I1/2
I1/2=ICQ+B0+0.5B1-0.5B2….
At point 3, ωt=Π/2,Ic
=ICQ
At point 4, ωt=2Π/3,Ic=I -1/2
I-1/2=ICQ+B0-0.5B1-0.5B2+B3-0.5B4+…..
At point 5,wt=Π ,Ic=Imin
Imin=ICQ+B0-B1+B2-B3+B4……
81. Higher Order Harmonic distortion:-
Solving these equations
B0=(Imax-2I 1/2+2I-1/2+Imin)/6-Icq
B1=(Imax+I 1/2-I-1/2-Imin)/3
B2=(Imax-2Icq+Imin)/4
B3=(Imax-2 I1/2+2I-1/2-Imin)/6
B4=(Imax-4I 1/2+6Icq-4I-1/2+Imin)/12
Hence the harmonic distortion coefficients can be
obtained as
Dn=|B0|/|B1|
82. POWER OUTPUT DUE TO DISTORTION:-
Now
Pac=B2
1R L /2
Hence the output power due to harmonic distortion is
(Pac)D =(B2
1Rl+ B2
2Rl+ B2
3Rl+…..)/2
=B2
1Rl(1+B2
2/B2
1+B2
3/B2
1+……)/2
(Pac)D=Pac(1+D2
2+D2
3+…….)
D2
=D2
2+D2
3+……..
(Pac)D=Pac(1+D2
)
83. POWER OUTPUT DUE TO DISTORTION:-
If the total harmonic distortion is 15%
i.e.
D = 0.15
(Pac)D=Pac(1+0.152
)=1.0225Pac
So,
There is 2.25%increases in power given to the load.
84. CLASS-B AMPLIFIER:-
In class-B power amplifiers, the transistor is so
biased that the output current flows only for half
cycle of the input signal.
It means that the transistor is forward biased for half
of the input cycle. In the negative half cycle of the
input signals, the transistor enters in to cut-off region
and no signal is produced at the output.
87. CLASS-B AMPLIFIER:-
As the collector current flows only for the 180
degree (half cycle) of the input signal. In this case
the transistor conduction angle is equal to
180degree as shown in fig.
As only a half cycle is obtained at the output, for full
input cycle, the output signal is said to be ‘distorted’
in class B operation. The efficiency of class B
amplifier is much higher than the class A amplifier.
88. POWER AND EFFICIENCY CALCULATIONS:-
Pin dc =Vcc Idc
Where,
Idc
= the average or direct current taken
from the collector supply.
= Icmax /Π
Thus
P in dc= Vcc Icmax / Π
90. CLASS-AB AMPLIFIERS:-
In this type, the transistor is so biased that the output
current flows for more than half, but less that the full
cycle. The transistor conduction angle is between
180degree and 360degree such a condition is
shown in fig. The Q point is very close to cut-off
value but well above X-axis.
92. CLASS-AB AMPLIFIERS:-
The output signal obtained in the class AB operation
is distorted. The efficiency of class AB amplifier is
more than class A but less than class B operation.
The class AB operation is important in eliminating
the crossover distortion.
93. Operation of Class AB amplifier:-
Ic
Vce
Q point
Vcc/RL Load
line
Output
signal of
voltage
Imax
94. 1. cross over distortion are not present.
2. efficiency is more than class A
configuration.
3. output per transistor is more than class A
operation.
4.non linear distortions are less than class B
amplifier.
Advantages:-
95. DISADVANTAGES:-
1. Efficiency is less than class B amplifier.
2. Lower output per transistor in comparison to
class B configuration.
3. Non linear distortions are more than class A
configuration.
96. CLASS-C AMPLIFIER:-
In class C amplifier, the transistor bias and signal
amplitude are such that the output current flows for
appreciably less than half cycle of the input signal.
Hence its conduction angle is up to 120 degree and
150 degree that is the transistor remains forward
biased for less than half the cycle.
Class C amplifier circuit consist of tuned circuit (L
and C tank circuit) in the output which is tuned to
desired RF frequency.
It select the fundamental and rejects the rest of the
harmonics.
98. CLASS-C AMPLIFIER:-
A class C power is biased to operate for less then
180° of the input signal cycle.
As shown in fig. the tuned circuit in the output
however, will provide a full cycle of output signal for
the fundamental or resonant frequency of tuned
circuit (L and C tank circuit) of the output.
99. CLASS-C AMPLIFIER:-
The use of such amplifiers is limited for a fixed
frequency, as occurs in communication circuits.
Operation of class C circuit is not intended primarily
for large signal or power amplifiers.
100. CLASS –C AMPLIFIER OPERATION:-
Ic
VceQ point
Vcc/RL
Input cycle of
current
Load
line
Output
signal of
votage
Vcc=Vceq
Imax
101. CLASS-C AMPLIFIER:-
In class C operation as the collector current flows for
less than 180 degree, the output is much more
distorted.
Due to this reason class C amplifiers are never used
for audio frequency amplifiers. But the efficiency of
class C operation is much higher and can reach
very close to 100%.
102. ADVANTAGES:-
1.The collector efficiency is very high (more than
80%). It is more than class A ,class B and class AB
operations.
2. Output delivered to load is free from harmonics
sience circuit is tuned to fundamental and harmonic
are rejected.
103. DISADVANTAGES:-
1.The output is not complete waveform. It is a
distorted waveform and distortions are more than
class A, class B and class AB configurations.
2. Use of transformer in output make the circuit
heavy, expensive and large in size.
104. CLASS-D AMPLIFIER:-CLASS-D AMPLIFIER:-
Since the transistor devices use to provide the
output are basically either OFF or ON, there will be
very little power loss due to their low ON voltage.
Hence most of the power supplied to the amplifier is
transferred to the load, the efficiency of the circuit is
typically very high. Power MOSFET devices have
been quite popular as the driver device for the class
D amplifier.
106. CLASS-D AMPLIFIER:-CLASS-D AMPLIFIER:-
The class D efficiency is largely determined by the
ratio of the load resistance to the total D.C. loop
resistance which is the sum of the rDS(ON) of the
MOSFET, wire resistance (including the output filter)
and the total resistance.
For highest efficiency, the MOSFET rDS(ON)
resistances shunt and filter resistances should be
small compared to the load resistance.
107. CLASS-D AMPLIFIER:-CLASS-D AMPLIFIER:-
In audio class D application, MOSFETS are
employed instead of 1GBTs and BJTs because the
switching frequencies required to keep distortion low
at 20KHz signal frequencies can exceed 160KHz
and neither the bipolar power transistors or 1GBts
switch efficiency at such high frequencies.
108. CLASS-D AMPLIFIER:-CLASS-D AMPLIFIER:-
Class D amplifiers are popular because of their very
high efficiency, an efficiency of over 90% is
achieved using this type of circuit.
A Class D amplifier is designed to operate with
digital or pulse type signals.
It is necessary to convert any input signal into plus
type waveform before using it to drive a large power
load and to convert the signal back to a sinusoidal
type signal to recover the original signal
109. CLASS-D AMPLIFIER:-CLASS-D AMPLIFIER:-
While the letter ‘D’ is used to describe the next type
of bias operation after class C, the D could also be
considered to stand ‘Digital’ since that is the nature
of signals provided to the class D amplifier.
Convert back to the sinusoidal-type signal
employing a low pass filter.
110. CLASS-A PUSH PULL AMPLIFIER:-
DEFINITION:-
The distortion introduced by non linearity discussed
earlier can be minimized by the circuit known as
push pull configuration and this amplifier is known
as push pull amplifier.
CONSTRUCTION:-
Two transistor are used (T1 and T2),both of these
transistor are identical. Their emitters are Connected
together .But bases and collector are connected are
in opposite ends of input and output transformer
(I.e.Tr1,Tr2).
112. CLASS-A PUSH PULL AMPLIFIER:-
Both the transformer Tr1 and Tr2 are center-tapped
transformers. Both Resistors R1and R2 provides
biasing arrangement.
Load is connected across secondary of Tr2.To
ensure that maximum power is delivered to the load
from amplifier ,turns ratio of Tr2 is so chosen that
output impendence of transistor matches to that of
load impedance.
113. CLASS-A PUSH PULL AMPLIFIER:-
Operation:-
As shown in circuit diagram, Ic1 and Ic2 flow in opposite
direction through the primary of transformer(Tr2). In
addition, Ic1 and Ic2 are equal in magnitude. So there
is no net d.c. component of collector current in primary
of transformer Tr2.
Hence there is no d.c. saturation in the transformer
core .This result increases in A.C. power output
compared with single transistor operation.
114. CLASS-A PUSH PULL AMPLIFIER:-
When a.c. signal is applied to the input, during
positive half cycle of the input a.c. signal, the base
of transistor T1 is more positive than the base of
transistor T2.
Collector currents are always in phase with base
currents. Hence the collector current Ic1 increases
while Ic2 of transistor T2 decreases.
115. CLASS-A PUSH PULL AMPLIFIER:-
These currents(Ic1 and Ic2) flow in opposite direction in
the two halves of the center-tapped output
transformer(Tr2).Due to this,the magnitude of voltage
induced in the load will be proportional to the
difference of collector currents(Ic1 and Ic2).
Similarly, for the negative half of the input a.c.signal,
the magnitude of voltage induced in the load will be
proportional to the difference (Ic1 and Ic2).Thus, for the
complete a.c signal, there is an induced a.c. voltage
in the secondary of output transformer Tr2 and a.c.
power is delivered to the load.
116. CLASS-A PUSH PULL AMPLIFIER:-
From the above discussion, it is seen that when Ic1
increases, Ic2 decreases and when Ic2 increases, Ic1
decreases.this means that one transistor is pushed
into conduction and other is pulled out of
conduction. Hence the name push-pull amplifier.
Biasing arrangement is so that the collector current
flows through 3600. Hence name class-A push-pull
amplifier.
117. DISTORTION IN CLASS-A PUSH-PULL
AMPLIFIER:-
Ib1=Ib sin wt
Ib2=Ib sin (wt+Π)
The collector current is represented as :
Ic=I0+I1sin wt+I2sin 2wt+I3sin 3wt
As the collector collector current of second
transistor is 180 out of phase. It can be
represented as :
118. DISTORTION IN CLASS-A PUSH-PULL
AMPLIFIER:-
Ic2=I0+I1sin(wt+Π)+I2sin2(wt+Π)+I3sin3(wt+Π)
Ic2=I0-I1sinwt+I2sin2wt-I3sin3wt
In the push-pull amplifier, the output voltage induced
in the secondary of the output transformer is
proportional to the two collector currents (Ic1-Ic2).
119. DISTORTION IN CLASS-A PUSH-PULL
AMPLIFIER:-
Hence
V0=K (Ic1-Ic2)
or V0=K (2I1sin2wt+2I3sin3wt+…….)
or V0=2K (I1sinwt+I3sin3wt+I5sin5wt+……)
where K is the constant of proportionality.
120. DISTORTION IN CLASS-A PUSH-PULL
AMPLIFIER:-
It is important to note that no even harmonic term is
appears in the equation. Hence all even harmonics
are eliminated from the output.
In harmonic distortion, the magnitude of second
harmonic contribute to most of distortion. As the
order of harmonic increases (i.e. third, fourth
harmonic and so on) distortion is less objectionable.
121. DISTORTION IN CLASS-A PUSH-PULL
AMPLIFIER:-
Second harmonic is considered to be most
objectionable. In push-pull amplifiers, all even
harmonics are cancelled.
Therefore, in the absence of second harmonic we
say that distortion in the output of a push-pull
amplifier is almost negligible in comparison to a
single ended power amplifier.
122. CLASS-A PUSH PULL AMPLIFIER:-
Advantages:-
1. Less distortion due to cancellation of even
harmonics.
2. We get more output per transistor for a given
amount of distortion.
3. The d.c. components of the collector current of
transistor T1 and T2 flows in opposite direction
hence there is no net d.c. magnetization or core
saturation.
123. CLASS-A PUSH PULL AMPLIFIER:-
Disadvantages:-
1. Two transformers used makes the circuit bulkier
and costlier.
2. Two hundred percentage identical transistors are
required, which is not possible in practical.
3. Since this is class-A, therefore, individually each
transistor has maximum efficiency of 50% and
hence the over-all efficiency of two transistors
together is also maximum 50%.
124. CLASS-B PUSH PULL AMPLIFIER:-
We have studied that class A amplifier removes some
of the drawbacks of single ended transistor coupled
amplifier, but efficiency is only 50%.Class-B amplifier
helps in getting higher efficiency and higher output
power.
Circuit is similar to class-A amplifier except that the
biasing resistance R1&R2 are absent so no biasing is
provided to both transistors because of transistors are
to work in class-B operation. in this operating point is
set at the cutoff region for which no biasing is required.
126. CLASS-B PUSH PULL AMPLIFIER:-
OPERATION:-
The input transformer is a phase splitter providing
two signals 180º out of phase ,one going to each of
transistors.
When there is no signal, both the transistors are cut-
off, hence no current is drawn by either of them.
Thus there is no power wasted during this condition.
127. CLASS-B PUSH-PULL AMPLIFIER:-
Now consider that an a.c. signal (Vs=Vosinωt) is
applied at input .
During positive half cycle of input signal i.e. Vs goes
positive ,the induced voltage on the secondary of
input transformer becomes positive for the base of T1
and is negative for T2 thus T1 conducts during
positive half cycle and during this T2 does not
conducts.
128. CLASS-B PUSH-PULL AMPLIFIER:-
In the negative half cycle when Vs goes negative T1
does not conducts but T2 conduct . In figure the
wave shapes shown for I1 and I2 each remaining
zero for 180º and conducts for next 180º (similar to
rectified half waves).
Due to transformer action the current induced in the
secondary is a full wave.
129. CLASS -B PUSH PULL AMPLIFIER:-
D.C. power input:-
D.c. power output of the two transistors is
P(d.c.)=2×power input to the transistor
=2[I(d.c)×V cc]
we know
Idc=Im / π (for half wave)
therefore
Pdc.=(2Im/π) × Vcc
130. CLASS-B PUSH PULL AMPLIFIER:-
A.C. power outputA.C. power output :-:-
The a.c power output using peak value is given asThe a.c power output using peak value is given as
P ac= Vm Im/2P ac= Vm Im/2
P ac=(V cc-V min)× Im/2P ac=(V cc-V min)× Im/2
Efficiency:-Efficiency:-
This can be calculated using basic equationhis can be calculated using basic equation
%η = ( Pac/Pdc )×100%η = ( Pac/Pdc )×100
= { [Im/2×(Vcc-Vmin) ]/ [2/π× ImVcc] }×100= { [Im/2×(Vcc-Vmin) ]/ [2/π× ImVcc] }×100
= { [ π(Vcc -Vmin)] / [4Vcc] }×100= { [ π(Vcc -Vmin)] / [4Vcc] }×100
131. CLASS-B PUSH PULL AMPLIFIER:-
Maximum Efficiency:-
The maximum efficiency arises when Vmin = 0.
Therefore,
%ηmax = [(πVcc) / (4Vcc)]×100
%ηmax = 78.5%
Thus maximum efficiency possible for class-B push
pull amplifier is 78.5%.this is more than class-
A(50%).This increase is due to standing current
being zero and hence no loss of power during the
cut off half cycle.
132. CLASS-B PUSH PULL AMPLIFIER:-
Maximum power DissipationMaximum power Dissipation:-:-
( Pd )max = [4/π² (Pac) max ]1/2( Pd )max = [4/π² (Pac) max ]1/2
= 2/π²(Pac) max= 2/π²(Pac) max
133. CLASS-B PUSH PULL AMPLIFIER:-
Advantages:-
• Efficiency is much higher than class-A .
• When no input signal power dissipation is zero .
• Even harmonics gets cancelled, this reduces
harmonic distortions .
• As the d.c component of current flows in
opposite direction through the primary windings , there
is no d.c saturation of the core.
• Due to transformer , impedance matching is possible
.
• Ripple present in supply voltage also gets
eliminated .
134. CROSSOVER DISTORTION:-
Crossover distortion in the output signal refers to the
fact that during the time when input signal crossover
from positive to negative (or negative to positive)
,there is some nonlinearity in the output signal.
This is due the fact that as long as the magnitude of
input signal is less than cut-in voltage of base
emitter junction of transistor (0.7v for Si & 0.2 for
Ge), the collector current remain zero and transistor
remain in cut-off region.
135. CROSSOVER DISTORTION:-
Hence there is a period between the cross over of
the half cycles of the input signal,for which none of
the transistor is active & the output is zero.
Thus the output signal does not follow the inputThus the output signal does not follow the input
signal and hence get distorted. Such distortion issignal and hence get distorted. Such distortion is
crossover distortion.crossover distortion.
Crossover distortion is eliminated in class-ABCrossover distortion is eliminated in class-AB
amplifier.amplifier.
139. COMPLEMENTRY SYMMETRY CLASS –B
PUSH PULL AMPLIFIER:-
Circuit is as shown in diagram. This does not use a
input or output transformer .Input transformer has
the function of providing two inputs 180º out of
phase, which makes only one transistor (T1 or T2)
to conduct at a time.
140. COMPLEMENTRY SYMMETRY CLASS –B
PUSH PULL AMPLIFIER:-
However using complementary transistor (one NPN
other PNP) if we introduce same input to these
transistor, two collector currents of transistors would
be 180 º out of phase .
Thus avoiding transformer in the push pull
amplifier circuit . Also the output transformer is
avoided using two separate but equal power
supplies (Vcc1 and Vcc2) .
143. COMPLEMENTARY SYMMETRY
CLASS-B PUSH PULL AMPLIFIER:-
Operation:-
In positive half cycle of input T1 is forward biased
hence conducts ,T2 is reversed biased hence does
not conducts . This results into positive half cycle
across load RL as in figure .
Just opposite in negative half cycle of input i.e.
T2conducts and T1 being reverse biased does not
conduct.
144. COMPLEMENTARY SYMMETRY CLASS –B
PUSH PULL AMPLIFIER:-
This results into negative half cycle across load RL.
Thus I1 and I2 flow in one half cycle each but flow
through RL . Hence total current through RL is in both
half cycles, a complete cycle of output signal comes
across the load .
As in figure
145. COMPLEMENTARY SYMMETRY CLASS –
B PUSH PULL AMPLIFIER:-
Advantages:-
1.As the circuit is without transformer so its weight ,
size and cost are less.
2.Frequency response improves due to transformer
less circuit .
147. THERMAL RESISTANCE:-
It is the resistance in which heat flow
between two temperature point.
Pt= T1-T2
Q
Where
Q = Thermal resistance
148. VARIATION OF PD VERSUS
TEMPERATURE:-
Q
Temperature
P.D
(watts)
149. QUASI COMPLIMENTARY SYMMETRY PUSHQUASI COMPLIMENTARY SYMMETRY PUSH
PULL AMPLIFIER:-PULL AMPLIFIER:-
It is similar to complimentary symmetry
except it uses transistor pair in each NPN and
PNP transistor.
Above pair in known to be “Darlington pair”
and below pair is know to be “feedback pair”.
151. OPERATION:-OPERATION:-
AB operation is to be performed ,base potential of`
T2 must be higher than potential of point k ,while the
base potential of T3 must be lowered than that of
point K .this is accomplished by adjusting of biasing
of T1.
When no signal is applied at ten base of transistor
t1.capacitor “C” charges to potential of point K i.e.
Vcc/2.
152. OPERATION:-OPERATION:-
When signal is applied to the amplifier and positive
half cycle appears at the base of T1,T1 conducts
base potential of T3 is lowered , because point B3 is
grounded due to conduction of T1. Thus T1 and T2
are ON and T3 is in cutoff .Capacitor C charges
additionally via transistor T2 and load. Current is
delivered to load.
During negative half cycle ,T1 and T2 becomesDuring negative half cycle ,T1 and T2 becomes
OFF and T3 becomes ON therefore , capacitorOFF and T3 becomes ON therefore , capacitor
charges through T3 and load .Thus ,signal power ischarges through T3 and load .Thus ,signal power is
delivered to the load.delivered to the load.
154. Q.1 :- A power transistor working in a class-A operation is
supplied from a 12-volt battery if the maximum collector current
change is 100mA, find the power transferred to a 5ohm
loudspeaker if it is:
(1)Directly connected in the collector:
(2)Transformer coupled for maximum power transfer.
Also find the turn ration of the transformer in (2)case.
ANS:-
CASE 1: When loudspeaker is directly connected in the
collector
Maximum voltage across loudspeaker
= ΔIcRL= 100mA*5ohm = 500mV
155. CASE 2: When loudspeaker is transformer coupled
Output impedance of the transformer
=ΔVce/ΔIc =12/100mA=120ohm
For maximum power transfer the load resistance
referred to primary side (i.e.RL) must be equal to output
impedance of the transistor
So RL=120
156. We know that turns ratio is given by
Turns ratio (N) = (R’
L/RL)1/2
= (120/5)1/2
= 4.898
Now secondary voltage i.e. voltage across the speaker
Vs=VP/N=VCC/N=12/4.898=2.45V
Load current= Vs/RL=2.45/5=0.489
So power transferred to speaker =ILVL
= ILVL=2.5*0.49=1.2005W
=1200mW
157. Q 2:- A single ended class-A amplifier has a transformer
coupled load of 8 ohm. If the transformer turns-ratio(N1/N2) is
10,determine the maximum power delivered to the load. Take a
zero signal collector current of 500mA.
ANS:-
Given that RL=8 ohm, N=10 and ICQ=500mA
The load resistance seen by the primary of the transformer
R’L= N2
RL=10*10*8= 800 ohm
So maximum power delivered to the 8 ohm loud speaker
Po= 0.5*I2
CQR’L=(0.5)*(500*.001)(800) = 200 W
158. Q 3:- When a sinusoidal signal is fed to an amplifier, the output
current is given by
ic=15 sin 400t + 1.5 sin 800t + 1.2 sin 1200t + 0.5 sin 1600t ,
calculate
(1) second third and fourth percentage harmonic distortion.
(2) percentage increase in power due to distortion.
ANS:-
(1)Percentage harmonic distortions of various components are
given by
D2=(B2/B1)*100=(1.5/15)*100=10%
D3=(B3/B1)*100=(1.2/15)*100=8%
D4=(B4/B1)*100=(0.5/15)*100=3.33%
160. Q 4:- A complementary class B power amplifier uses a 15 volt
d.c. supply with a sinusoidal input, a maximum peak to peak of
24 volt is desired across a load of 100 ohm find the power
dissipated by each transistor.
ANS:- Peak value of current is
Ipeak=Vpeak/RL=(24/2)/100=0.12A
DC power drawn from battery
Pdc=Vcc*Idc=15*(2/π*0.12)=1.146 Watts
161. Thus the maximum efficiency possible in directly
coupled series fed class-A amplifier is just 25%
(ideally). In practical it is less than 25%.
162. Therefore a.c. power delivered to load
= 1/2( V2
peak/RL)=1/2(12*12/100)=0.72 Watts
Hence power dissipated in both the transistors
= 1.146-0.72=0.426 watts
Therefore, power dissipated by each transistor
=0.426/2=0.213 Watts
= 213 mW
163. Q 5:- For a single stage class A amplifier, Vcc=20 volt, VCEQ=10
Volt, ICQ=600mA and collector load resistor RL=16 ohm ,The ac
output current various by (+-)300 mA, with the ac input
signal.
Determine
(1)Power supplied by the d.c. source to amplifier or d.c. power
input to amplifier.
(2)D.C. power consumed by the load resistor.
(3)D.C. power delivered to transistor.
(4) Output power ac or ac power developed across the load resistor.
(5)Collector efficiency.
(6)Overall efficiency.
164. ANS:-
(1)Power supplied by the dc source to amplifier circuit
(Pin)dc=VCCICQ
= 20*600*0.001=12 Watts
(2)d.c. power consumed by the load resistor
PRc=I2
CQ*RC=(600*0.001)2
*16=5.76 Watts
(3)d.c. power delivered to the transistor
Ptr=(Pin)dc-PRc=6.24 Watts
165. (4) A.C. power developed across load resistor
(Po)ac=I2
rmsRc=(Im/1.404)2
Rc
=(.3/1.404)2
*16=0.72 Watts
(5) Collector efficiency
(Po)ac/Ptr*100=(0.72/6.24)*100=11.5%
(6) Overall efficiency
((Po)ac/Pin)*100=0.72/12*100=6%