Understanding class A & B amplifiers

In summary, Class A amplifiers are commonly used for small-signal amplification but are not very efficient. They can only achieve a theoretical maximum of 50% efficiency with inductive output coupling and 25% with capacitive coupling. On the other hand, Class B amplifiers only amplify half of the input wave cycle but have a maximum theoretical efficiency of 78.5%. This is because the amplifying element is switched off half of the time, resulting in improved efficiency. However, this also causes distortion. Biasing is important in Class A amplifiers to prevent distortion and decrease output swing, and the efficiency refers to the percentage of power delivered to the load from the DC supply.
  • #1
darkwhite87
18
0
I have read some texts myself but the explanations i read still leave me some queries. Below I have copied some text from wiki. From the text is in bold and my queries are in italic. Can someone please help me with my understanding, THANKS!

Class A amplifiers are the usual means of implementing small-signal amplifiers. They are not very efficient; a theoretical maximum of 50% is obtainable with inductive output coupling and only 25% with capacitive coupling.
1. Does this mean Class A can only amplify small signals, and what range of volts would it be?
2. What does it mean by 50% efficient? how is efficiency calculated??

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%. This is because the amplifying element is switched off altogether half of the time, and so cannot dissipate power.
3. They say that the efficiency is increased because the amplifying element is switched off half of time! Then what's the point! Isnt this just the same as Class A except that it is only amplifying half of the signal, how can this be efficient??
 
Engineering news on Phys.org
  • #3
Class A amplifiers are usually mid point biased. This means that the output can vary widely about its midpoint. Biasing is in any other way can result in distortion and the output swing will decrease accordingly. Because of their poor efficiency, they are used as small signal or low power amplifiers.

The efficiency refers the percentage of power drawn from the DC supply that is actually delivered to the load. You can refer to here for more talk on efficiency.

The efficiency for a class B amp comes with the push pull output stage. This simply means that only one transistor is conducting for a given half of the output signal. The fact that they don't conduct fully at the same time makes it efficient. The key thing to note when analyzing this amplifier for efficiency is to assume that no base current flows and the transistor is biased just inside the cutoff region.
 

1. What is the difference between class A and class B amplifiers?

Class A amplifiers are designed to provide the most accurate and high-quality sound reproduction, with a constant current flow and low distortion. Class B amplifiers, on the other hand, have a higher efficiency but also have some distortion due to their use of two transistors that alternate handling the positive and negative portions of the audio signal.

2. Which type of amplifier is better for audio applications?

This depends on the specific needs and preferences of the user. Class A amplifiers are better for high-fidelity audio and critical listening, while class B amplifiers are more suitable for applications where efficiency is important, such as in portable devices or live performances.

3. How do class A and class B amplifiers handle power consumption?

Class A amplifiers have a continuous flow of current, meaning they consume a constant amount of power regardless of the volume level. Class B amplifiers, on the other hand, only draw power when there is an audio signal present, making them more efficient in terms of power consumption.

4. Can class A and class B amplifiers be used together?

Yes, it is possible to use both class A and class B amplifiers in the same audio system. This is known as a class AB amplifier, which uses a combination of both classes to achieve a balance between sound quality and efficiency.

5. What are the advantages and disadvantages of class A and class B amplifiers?

Class A amplifiers have the advantage of providing the highest quality sound, but they are less efficient and generate more heat. Class B amplifiers have a higher efficiency, but they also have some distortion and are not suitable for low volume listening. It ultimately depends on the specific needs and preferences of the user.

Similar threads

Mosfet, Mesfet vs Bipolar transistors in RF circuits
    • Electrical Engineering
Replies
28
Views
3K
Using a low voltage supply in a class B amplifier
    • Electrical Engineering
Replies
25
Views
2K
NPN transistor and how it operates....
    • Electrical Engineering
Replies
11
Views
1K
Amplifier Comparison: CE, CC, and CB Types Examined - Study Guide"
    • Electrical Engineering
Replies
14
Views
3K
Can I use Op Amps to amplify both DC and AC signals?
    • Electrical Engineering
Replies
6
Views
2K
Photomultiplier Tube Destroying Amplifiers - Suggestions?
    • Electrical Engineering
Replies
4
Views
3K
Help -- car stereo is acting up with hand made amplifier
    • Electrical Engineering
Replies
23
Views
4K
Audio amp for sonoluminescense
    • Electrical Engineering
Replies
7
Views
1K
Antenna for a specific frequency ?
    • Electrical Engineering
Replies
12
Views
10K
Understanding EM Wave Transfer when Person Touches Amplifier Input
    • Other Physics Topics
Replies
2
Views
1K

Hot Threads

Recent Insights

Back
Top