In Class – A amplifier, the output current flows for
the full cycle of the input signal
Class-A Amplifier Output Current Explanation
A Class-A amplifier is a type of electronic amplifier where the active device (like a transistor) conducts for the entire cycle of the input signal. This means that the output current flows continuously, replicating the full waveform of the input signal.
Amplifier Operation in Class-A
In a Class-A amplifier, the transistor is biased such that its quiescent operating point (Q-point) is located approximately in the middle of the load line. This central biasing ensures that the transistor remains in its active region for the entire duration of the input signal's positive and negative swings. As a result, the transistor is always conducting, allowing the output current to flow for the full $360^{\circ}$ of the input cycle.
- Conduction Angle: The defining characteristic of a Class-A amplifier is its $360^{\circ}$ conduction angle, meaning the output current flows for the entirety of the input waveform.
- Linearity: Due to continuous conduction, Class-A amplifiers offer excellent linearity and very low signal distortion, making them suitable for high-fidelity audio applications.
- Efficiency: While offering high fidelity, Class-A amplifiers are known for their low power efficiency. A significant amount of power is dissipated as heat even when there is no input signal, because the device is always conducting a quiescent current.
Comparing Amplifier Classes
To better understand the distinct characteristic of a Class-A amplifier, it's helpful to compare its conduction angle with other common amplifier classes:
| Amplifier Class | Conduction Angle | Output Current Flow |
|---|---|---|
| Class-A | $360^{\circ}$ | Flows for the full cycle of the input signal. |
| Class-B | $180^{\circ}$ | Flows for half the cycle of the input signal. |
| Class-AB | Greater than $180^{\circ}$ but less than $360^{\circ}$ | Flows for slightly more than half, but less than the full cycle. |
| Class-C | Less than $180^{\circ}$ | Flows for less than half the cycle of the input signal. |
Therefore, based on the fundamental operation principles, in a Class-A amplifier, the output current flows for the full cycle of the input signal, ensuring a complete and undistorted reproduction of the waveform.
Important Questions from Power Amplifier
Arrange the given power amplifiers in the order of increasing power efficiency.
A. Class A
B. Class AB
C. Class B
D. Class C
E. Class D
Choose the correct answer from the options given below:- The IC CA810 can be used as power amplifier in many applications. Which is the circuit this IC cannot be used?
Arrange the following amplifiers as per their efficiency from highest to lowest
A. class B amplifier
B. class C amplifier
C. class A amplifier
D. class AB amplifier
E. class D amplifier
Choose the correct answer from the options given below :
In a class A large signal amplifier with RL as a load resistance, Im and Vm represents the peak sinusoidal current and voltage, the output power is
Assertion (A) : A sinusoidal signal applied to the input of an ideal class A amplifier usually does not produce an exact replica of the input signal waveform.
Reason (R) : This variation is caused due to non-linearity in the characteristics of the transistors.
Select your answer using the codes given below.
