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on video How does an Amplifier Work? (Class-B & AB)

 



Both the Class B amplifier and the Class AB amplifier have an output stage comprising of two transistors whose outputs are configured in such a way as to reconstruct the full 360o input waveform with or without distortion.

The purpose of any amplifier is to produce an output which follows the characteristics of the input signal but is sufficiently large enough to supply the needs of the load connected to it. We have seen that the power output of an amplifier is the product of the voltage and current, (P = V*I) applied to the load, while the power input is the product of the DC voltage and current taken from the power supply.

Although the amplification of a Class A amplifier, (where the output transistor conducts 100% of the time) can be high, the efficiency of the conversion from the DC power supply to an AC power output is generally poor at less than 50%.

However if we modify the Class A amplifier circuit to operate in Class B mode, (where each transistor conducts for only 50% of the time) the collector current flows in each transistor for only 180o of the cycle. The advantage here is that the DC-to-AC conversion efficiency is much higher at around 75%, but this Class B configuration results in crossover distortion of the output signal which could be unacceptable.


 



Both the Class B amplifier and the Class AB amplifier have an output stage comprising of two transistors whose outputs are configured in such a way as to reconstruct the full 360o input waveform with or without distortion.

The purpose of any amplifier is to produce an output which follows the characteristics of the input signal but is sufficiently large enough to supply the needs of the load connected to it. We have seen that the power output of an amplifier is the product of the voltage and current, (P = V*I) applied to the load, while the power input is the product of the DC voltage and current taken from the power supply.

Although the amplification of a Class A amplifier, (where the output transistor conducts 100% of the time) can be high, the efficiency of the conversion from the DC power supply to an AC power output is generally poor at less than 50%.

However if we modify the Class A amplifier circuit to operate in Class B mode, (where each transistor conducts for only 50% of the time) the collector current flows in each transistor for only 180o of the cycle. The advantage here is that the DC-to-AC conversion efficiency is much higher at around 75%, but this Class B configuration results in crossover distortion of the output signal which could be unacceptable.


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