Electronics: push-pull amplifiers

[kopinator]

I am writing a paper on Classes A and B push-pull amplifiers and was wondering if anyone would be willing to share some valuable insight into this type of circuit, i.e. advantages, disadvantages, when and where they can be used, etc.. Also, I have been doing a lot of my own research into this, but I'm struggling to find a distinction between Class A and Class B that is clear and easy to understand. Would anyone be willing to enlighten me on those differences?
Thank you!

 

[Svein]

I'm struggling to find a distinction between Class A and Class B that is clear and easy to understand. Would anyone be willing to enlighten me on those differences?

I will use transistor amplifiers in my examples.

• Class A amplifiers: Both upper and lower transistors conduct the whole time, just varying the amount of current they conduct.
• Class B amplifiers: Upper transistor cuts off when the lower conducts and vice versa. Creating a smooth transition between the two states is difficult, therefore class AB is more popular (both transistors conduct when the output goes through zero and some way beyond)
• Class C amplifiers: Only one transistor conducts at any time. No transistor conducts when the output goes through zero (only useful for RF amplifiers)
• Class D amplifiers: "Digital" amplifiers - the signal is converted to pulse width modulation and fed to the loudspeakers more or less directly. The loudspeakers act as a low pass filter and recreates the signal.

 

[nsaspook]

The conduction angle is related to how long during the entire waveform the output stage transistor(s) behaves as a variable resistance (using power) in a divider with the load resistance and how long it operates switched off with 'no' power dissipated in the transistor. In the case of digital modes the 'ON' power used by the transistor is related to the usually small about of voltage drop across the device when saturated so it's not a linear resistance following the signal and efficiency is much higher because of that.

 

[kopinator]

Wow, that's great! Thank you for your help. I can turn this into another double-spaced page of info. Thanks!

 

[kopinator]

Actually, I have one more question: The Class B is more efficient, but has more distortion. Why is that?

 

[nsaspook]

Actually, I have one more question: The Class B is more efficient, but has more distortion. Why is that?

Svein has the answer in that post.