op amp question

[danrogers]

Hi all. Ive had some help on here in making a circuit using an op amp and im now trying to understand how its working.

What are the main diferences between class a, and class b amps?

 

[Mikebits]

Have a look here. **broken link removed**

 

[danrogers]

thanks Mikebits, I will have a read of that. I was looking for something with diagrams but failed to find much.

 

[Mikebits]

How about this?

Class A.
**broken link removed**
Class B

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Also Class B.
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Idea Class A conduct for full cycle of input waveform. Class B for half. Class B is common in pushpull configuration.

 

[Nigel Goodwin]

thanks Mikebits, I will have a read of that. I was looking for something with diagrams but failed to find much.

As you're asking about opamps it's pretty irrelevant, as it's part of the IC design. But basically (for non-opamps) it's just a question of biasing.

 

[danrogers]

I meant waveforms so I can try and understand what the i/o is doing but thats helped thanks

Its been a while since I did math at school and I think my brain has seen better days, I'm messing with some simulated op amp circuits and Im trying tio work out Rout resistance. I have the voltage and the current, so I need do V/I but how do I work out 1uV/1.3mA?

thanks

 

[MikeMl]

Aren't OpAmps Class B (actually AB1)? They have a totem pole output stage which can actively both source and sink current. The output stage is biased so both transistors are lightly turned on, so if the output is unloaded, the quiescent current is small but finite. They have some crossover distortion.

 

[crutschow]

Mikebits showed the circuit types that are used for Class B RF output circuits where the half-wave pulses are used to excite an RF tank circuit tuned to the output frequency.

The type of Class B circuit that MikeMl described are used in op amp output stages or in audio power amp output stages.

 

[Nigel Goodwin]

Mikebits showed the circuit types that are used for Class B RF output circuits where the half-wave pulses are used to excite an RF tank circuit tuned to the output frequency.

The type of Class B circuit that MikeMl described are used in op amp output stages or in audio power amp output stages.

They are the same thing, and transmitter stages are normally class C anyway.

It's purely a matter of biasing, the first diagram 'class A' is only class A because the output waveform shows it as such, it could just as easily be class B, depending on the base resistor values.

 

[Hero999]

Aren't OpAmps Class B (actually AB1)? They have a totem pole output stage which can actively both source and sink current. The output stage is biased so both transistors are lightly turned on, so if the output is unloaded, the quiescent current is small but finite. They have some crossover distortion.

Yes most op-amps are class AB but some are A and you can get some which are B.

EDIT:
This question isn't important for practical purposes, unless you're designing your own op-amp for educational purposes.

 

[THESTOCKSGUY]

https://www.electro-tech-online.com/custompdfs/2010/05/op-amps.pdf

**broken link removed**

**broken link removed** (STARTS AT PAGE 6)

 

[danrogers]

thanks for all the links!