TLDR;
This video provides a detailed explanation of Class AB amplifiers, including their definition, operation, circuit diagram, and advantages. It emphasizes how Class AB amplifiers bridge the gap between Class A and Class B amplifiers, offering improved efficiency compared to Class A while minimizing crossover distortion, a common issue in Class B amplifiers.
- Class AB amplifiers operate with a conduction angle between 180 and 360 degrees.
- They are designed to reduce crossover distortion found in Class B amplifiers.
- The efficiency of Class AB amplifiers lies between 50% and 78.5%.
Introduction to Class AB Amplifiers [0:00]
Class AB amplifiers operate between Class A and Class B, with the transistor conducting for more than 180 degrees but less than 360 degrees of the input AC signal cycle. The amplifier is defined by its output signal being obtained for more than 180 degrees but less than 360 degrees for a full cycle of the AC input signal. The operating point (Q-point) of the transistor in a Class AB amplifier is positioned above the x-axis but below the midpoint of the load line, differing from Class A where it's at the midpoint and Class B where it's on the x-axis.
Operation of Class AB Amplifiers [2:42]
Class AB amplifiers are primarily used to eliminate crossover distortion, a significant drawback of Class B amplifiers. To achieve this, a small amount of current is maintained even when the input signal is zero, ensuring that the transistor starts conducting immediately upon receiving an AC input signal. The circuit diagram of a Class AB amplifier is similar to that of a Class B amplifier but includes emitter stabilizing resistors. These resistors bias the transistors, allowing them to conduct for more than 180 degrees but less than 360 degrees, positioning the Q-point between the ranges of Class A and Class B.
Advantages of Class AB Amplifiers [4:19]
The Q-point of a Class AB amplifier is located between the active region of Class A and the cutoff region of Class B amplifiers. This design results in an efficiency greater than that of Class A amplifiers but slightly less than that of Class B amplifiers, all while avoiding crossover distortion. The efficiency of Class AB amplifiers typically ranges from greater than 50% to less than 78.5%. The primary advantage of Class AB amplifiers is their ability to eliminate crossover distortion, making them a preferred choice in audio amplification and other applications where signal fidelity is crucial.