What is the maximum theoretical efficiency of a class B amplifier?
78.5%Although the maximum theoretical efficiency of a class B amplifier is 78.5%, typical efficiency levels are much lower.
What is the maximum conversion efficiency of Class B power amplifier?
(≈ 78.5%)When Class-B amplifiers amplify the signal with two active devices, each operates over one half of the cycle. Efficiency is much improved over class-A amplifiers. Class-B amplifiers are also favoured in battery-operated devices, such as transistor radios. Class B has a maximum theoretical efficiency of π/4 (≈ 78.5%).
Which amplifier has the highest theoretical efficiency?
Complete answer: A class D amplifier is the most efficient type of amplifier.
Which power amplifier has a theoretical efficiency of 50%?
Class A amplifierExplanation: Class A amplifier has a theoretical efficiency of 50%.
Why do Class B amplifiers have high efficiency?
In the class B amplifier, there is no DC base bias current as its quiescent current is zero, so that the dc power is small and therefore its efficiency is much higher than that of the class A amplifier.
What is a Class B amplifier used for?
These are mainly used in the low-cost design. These amplifiers are very significant as compared to the class-A amplifiers. This type of amplifier suffers mainly from distortion if the level of signal is low. These are mainly used in two complementary transistors like bipolar and FET.
What is the maximum theoretical efficiency?
The Carnot Efficiency is the theoretical maximum efficiency one can get when the heat engine is operating between two temperatures: The temperature at which the high temperature reservoir operates ( THot ).
What are the characteristics of class B amplifier?
Class B Amplifier operation has zero DC bias as the transistors are biased at the cut-off, so each transistor only conducts when the input signal is greater than the Base-emitter voltage. Therefore, at zero input there is zero output and no power is being consumed.
Which power amplifier has the lowest collector efficiency?
Class A amplifier has lowest efficiency and the efficiency of different amplifiers are given below.
What is the collector circuit efficiency of a class B push pull amplifier if VM peak load voltage?
Since, the transistor is on for alternating half-cycles, it effectively acts as a half-wave rectifier . Thus, the maximum collector efficiency of class B power amplifier is 78.5% .
What is the difference between Class A and Class B amplifier?
Class A amplifiers can be made very linear, but with limited efficiency. In theory, a class A amp can achieve 50% efficiency with inductive output coupling or 25% with capacitive coupling. Class B amplifiers are subject to “crossover” distortion, but efficiency runs theoretically as high as 78.5%.
What is the output of a Class B amplifier for sinusoidal input?
half sinusoidal2. What is the output of a class B amplifier for sinusoidal input? Explanation: If Q-point is in cut-off, then IC varies only in the positive direction, for saturation, it varies in the negative direction. So the output of Class B amplifier is half sinusoidal.
How do you calculate the efficiency of a class B amplifier?
2:165:56Class B Amplifier Efficiency Calculation - YouTubeYouTubeStart of suggested clipEnd of suggested clipSo that's three volt peak output to give us a peak current will be three volts divided by the loadMoreSo that's three volt peak output to give us a peak current will be three volts divided by the load resistor which in this case is 10 ohms.
What is the efficiency of power amplifier?
Power-Added Efficiency (PAE) expresses the overall efficiency of the power amplifier, including the effect of the input power. PAE is usually expressed as a percent. For example, a power amplifier having an output power of 10 W, an input power of 0.5 W and DC power of 30 W would have a PAE = (10-0.5)/30 = 32%.
What is the approximate efficiency of a class B linear RF am amplifier?
Class B amplifiers only amplify half of the input wave cycle. As such they create a large amount of distortion, but their efficiency is greatly improved and is much better than Class A. Class B has a maximum theoretical efficiency of 78.5%.
What is the efficiency of Class A amplifier?
50% efficiencyClass A amplifiers can be made very linear, but with limited efficiency. In theory, a class A amp can achieve 50% efficiency with inductive output coupling or 25% with capacitive coupling. Class B amplifiers are subject to “crossover” distortion, but efficiency runs theoretically as high as 78.5%.
Which class of amplifier improves the efficiency?
Hence the class B push-pull amplifier improves the efficiency than the class A push-pull amplifier.
What is the circuit of a push-pull class B amplifier?
The circuit of a push-pull class B power amplifier consists of two identi cal transistors T 1 and T 2 whose bases are connected to the secondary of the center-tapped input transformer T r1. The emitters are shorted and the collectors are given the V CC supply through the primary of the output transformer T r2.
What happens when no signal is applied to the input of a class B push pull amplifier?
When no signal is applied at the input, the transistors T 1 and T 2 are in cut off condition and hence no collector currents flow. As no current is drawn from V CC, no power is wasted.
What is class B push pull amplifier?
The circuit arrangement of class B push-pull amplifier, is same as that of class A push-pull amplifier except that the transistors are biased at cut off, instead of using the biasing resistors. The figure below gives the detailing of the construction of a push-pull class B power amplifier.
What happens to the output transformer in a half cycle?
Hence for both the cycles, each transistor conducts alternately. The output transformer T r3 serves to join the two currents producing an almost undistorted output waveform.
How many transistors are in a push pull amplifier?
Here factor 2 is introduced as there are two transistors in push-pull amplifier.
When the collector current flows only during the positive half cycle of the input signal, the power amplifier is known as?
When the collector current flows only during the positive half cycle of the input signal, the power amplifier is known as class B power amplifier.
What is a class B amplifier?
Class B amplifier is a type of power amplifier where the active device (transistor) conducts only for one half cycle of the input signal. That means the conduction angle is 180° for a Class B amplifier. Since the active device is switched off for half the input cycle, the active device dissipates less power and hence the efficiency is improved. Theoretical maximum efficiency of Class B power amplifier is 78.5%. The schematic of a single ended Class B amplifier and input , output waveforms are shown in the figure below.
Why is Class AB not practical?
Single ended Class AB configurations are not practical just because a major portion of one half cycle will be missing at the output. Just like the Class B configuration, push-pull mechanism is essential for realizing practical Class AB power amplifiers. Circuit diagram of a typical Class AB push-pull amplifier is shown in the figure below.
What happens to the input signal when the transistors are at zero?
Since both the transistors are slightly conducting at zero input, no information in the input signal is lost at the output during the zero-cross ing of the input signal and thus cross-over distortion is completely eliminated at a cost of slightly reduced efficiency.
What is it called when the input signal is less than 0.7V?
Since the active elements start conduction only after the input signal amplitude has risen above 0.7V, the regions of the input signal where the amplitude is less than 0.7V will be missing in the output signal and it is called cross over distortion. The schematic representation of cross-over distortion is shown in the figure below. In the figure, you can see that the regions of the input waveform which are under 0.7V are missing in the output waveform.
Which transistor conducts the positive half cycle?
The NPN transistor alone will conduct the positive half cycle and PNP transistor alone will conduct the negative half cycle. Slight pre-biasing is given to the transistors using the network comprising of resistors R1, R2 and biasing diodes D1 and D2.
Is transformer coupling practical?
Transformer coupling is not practical in case of huge loads.
Can capacitor coupling eliminate DC components?
Capacitive coupling can eliminate DC components but it is not practical in case of heavy loads.
What is the maximum possible collector circuit efficiency for class B amplifier?
Equation 5 shows that the maximum possible value of collector circuit efficiency for class B amplifier is i.e. 78.5%. This maximum theoretical value is higher than the corresponding value of 50% for class A transformer coupled amplifier.
How does collector circuit efficiency compare to class B amplifier?
Basically, this high value of collector circuit efficiency in class B amplifier becomes possible because of the fact that in class B amplifier, current is zero with zero excitation whereas in class A amplifier, there is drain from V CC source even at zero signal. It is worth nothing that in a class B amplifier, collector dissipation is zero signal and increases with increase of signal magnitude while in a class A amplifier, collector dissipation is maximum with zero signal and decreases with increases of signal magnitude.
What is the collector dissipation of zero excitation?
With zero excitation, V m = 0. Hence, as per equation 8, collector dissipation is zero with zero excitation. Using equation 8, it may be shown that the collector dissipation increases with increase of excitation and passes through a maximum at .
How many watts does a class A amplifier use?
On the other hand, in class A amplifier using parallel operation of two transistor to get the same output power of 50 watts, assuming maximum conversion efficiency of 50%, dc power requirement is watts. This complete power of 100 watts must be dissipated in the two transistors are zero signal. Thus, each transistor must be capable of dissipating 50 watts. Thus, with zero excitation, in class A operation there is a steady loss of 50 watts in each transistor whereas in class B amplifier the standby or zero excitation collector dissipation is zero. This clearly establishes the superiority of class B push pull operation over class A parallel operation.
How much power does a class B amplifier deliver?
For a class AB amplifier designed to deliver maximum power output of say 50 watts, P Dmax – 20 watts i.e. each transistor must be capable of dissipating 10 watts. Hence, we conclude that class B pushpull amplifier is capable of providing output power 5 times the power dissipation capability of each transistor.
What is collector dissipation in class B amplifier?
It is worth nothing that in a class B amplifier, collector dissipation is zero signal and increases with increase of signal magnitude while in a class A amplifier, collector dissipation is maximum with zero signal and decreases with increases of signal magnitude. In class B amplifier, the d.c.
What is total collector dissipation?
Total collector dissipation P D in both transistors is equal to the dc power input from collector supply voltage minus the power delivered to the load. Hence,
Transformer Coupled Class B Amplifier Circuit
The class B power amplifier’s efficiency is higher as compared to class A because, in class B, there is no DC base bias current because its quiescent current (IQ) is zero so that the DC power is very small. In a Class-B amplifier, the transistors are biased to cutoff, so that there is no power dissipation of transistor when there is no i/p signal.
Class B Amplifier Working
From the above circuit diagram, we can conclude that both the transformers like TR1 & TR2 are center-tapped. At the input, no signal is applied then both the transistors will be in the cut-off region, and thus no flow of current throughout the collector terminal. When no current is used from VCC, then there is no waste of power.
Class B Power Amplifier Solved Problems
Example1: Calculate the input power, o/p power & the efficiency for the class B amplifier which provides a peak signal of 20 V to a 16ohms speaker & 30V power supply.
What is the maximum theoretical conversion efficiency of a transformer coupled class A amplifier?
From equation (14) we find that the maximum theoretical conversion efficiency of a transformer coupled class A amplifier is 50% i.e. twice the maximum theoretical conversion efficiency of series fed class A Amplifier. In a transistor amplifier, V min lies close to the saturation region. Hence V min << V max. Hence, in practice, the collector circuit efficiency of a transformer coupled class A transistor amplifier is quite close to 50%.
What is the conversion efficiency of a series fed amplifier?
From Equation (12) we find that conversion efficiency for series fed class A amplifier approaches its maximum value of 25% when V min approaches zero. In actual practice, however, in considerably smaller than this value of 25%, typically value being only 15%.
What is the average input from a DC supply?
For present analysis, we assume a resistance load. Then the average input from the dc supply is V CC I C. Out of this total dc power, a part P D is dissipated in the collector of the transistor while the rest is absorbed by the output circuit and equal (I C2 R 1 + I c V c) where I c and V c are the rms values of output current and output voltage respectively and R 1 is the static load resistance. Then by the principle of conservation of energy,
Is the overall efficiency of a circuit smaller than the efficiency of a collector circuit?
It is the ratio of a.c. output power delivered to the load to the dc power from the output (collector) circuit source plus the dc power from the base circuit. Thus, overall efficiency is smaller than the collector circuit efficiency.
