Three working states of power amplifier tube
The low-frequency power output stage is classified into Class A, Class B, and Class C according to the working state of the power amplifier tube.
They have their own characteristics:
(1). The main advantage of Class A power output stage is low distortion, and the main disadvantage is low efficiency.
Its output power Po, power consumption PD, collector maximum power consumption Pcmax and efficiency are:
Po = Ec2 / 2RL PD = 2Ec2 / RL
Pcmax = 2Ec2 / RL = 4Po η = Po / PD = 1/4 = 25%
(2) The main advantage of Class B power output stage is high efficiency, and the main disadvantage is the existence of severe crossover distortion.
Its output power Po, power consumption PD, collector maximum power consumption Pcmax and efficiency are:
Po = Ec2 / 2RL PD = 2Ec2 / πRL
Pcmax = 2Ec2 / π2RL? 0.4Po η = Po / PD = π / 4 = 78%
(3). Class A and B power output stage absorbs the advantages of Class A and Class B, so it is widely used,
But its circuit structure is more complicated than Class A and Class B. As shown below:

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This section is the main content of this chapter. In this section, we have to master the formula method to calculate Q points and the graph method to calculate Q points.

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The low-frequency power output stage is classified into Class A, Class B, and Class C according to the working state of the power amplifier tube. They each have ...