Class S Amplifier

439

04:36:03

This kind of amplifier has been catching my eye lately. The ingenuity behind it is that the op amp at the left can be a low distortion class A amplifier working very linearly, and the only current draw it's going to see is to correct the distortions of the class B amplifier at the right (granted a good balance between the 100mOhm/10k bridge). The whole idea behind it is not to increase any efficiency levels, as the class A amplifier is going to draw some small amounts of current, but to help eliminate any sort of distortion that the class B amplifier can give off. I'm currently trying to design it with an LM3866 IC as the class B integrated equivalent, and a low distortion discrete class A amplifier working at some 250-300mA idle current. Rarely would the class A amplifier see an opportunity to give off so much current to correct the output, as a perfectly balanced system should ideally work with the class B amp as a current amplifier, and the class A amp as a voltage amp, with only correctional function. 

published 4 years ago

PTamas

4 years ago

You mean like the LM3886 from TI? How much output power will this amplifier have?

thebugger

4 years ago

Yes, LM3866 from TI. The output is suppressed with 4W by the 2x100mOhm resistors, so instead of 68W, you get 64W. The class A amplifier at the left only works to suppress distortions coming from LM3866, so it will not increase the overall power in any way.

sircube

4 years ago

The problem of these kind of design is about the slew rate of the second amplifier: usually it's poor with an integrated class AB amplifier as you suggest. The other issue, which is strictly related, is that when the cross-over point occurs there is a really high current demand from the output stage and a real bjt takes some time to turn on, it's not instant, due to capacitance of the junctions and Miller effect, and you will get an increasing distortion vs frequency curve.

thebugger

4 years ago

Exactly. This is why the amplifier at the left compensates only for such distortions.

sircube

4 years ago

Hmmm... I may have to study it deeper then, at the moment I may not be completely understandig it.

Antonio1961

4 years ago

👍

Antonio1961

4 years ago

You could include the input and output waveforms.

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