Amplifier with complementary output stages

halil06

Joined Apr 9, 2017
3
Hi,I have a problem with ab class amplifier for my school project.I know a little bit circuit components which has a specification in that circuit but I dont know how to make theoretical analiysis. Which formulas I need first for this circuit How to I calculate cuurents voltages and gain because its special circuit

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Jony130

Joined Feb 17, 2009
5,439
Did you analysis any BJT amplifier circuit ever before? Try to use a KVL and solve for DC operation point (treat the capacitor as a open circuit).

MrAl

Joined Jun 17, 2014
9,778
Hi,I have a problem with ab class amplifier for my school project.I know a little bit circuit components which has a specification in that circuit but I dont know how to make theoretical analiysis. Which formulas I need first for this circuit How to I calculate cuurents voltages and gain because its special circuit

View attachment 124301
Hi,

What else would help everyone here to answer your question is if you showed some work. That way we know what approximations are allowed in your coursework at this stage in your education. Without that, we might throw the simplest to the most complicated analysis at you, either of which you might not like because it does not fit the coursework requirement at this time.
So if you show a little work about what you have done so far, that would help.

shteii01

Joined Feb 19, 2010
4,644
Hi,

What else would help everyone here to answer your question is if you showed some work. That way we know what approximations are allowed in your coursework at this stage in your education. Without that, we might throw the simplest to the most complicated analysis at you, either of which you might not like because it does not fit the coursework requirement at this time.
So if you show a little work about what you have done so far, that would help.
Are you joking? Did you miss this part from OP: "but I dont know how to make theoretical analiysis". That right there tells me that they want us to do all the work. Anyone with the BSEE can just stop after reading that and go do something else. Because I have BSEE I am not going to try to cram 5 months of course work into this thread.

MrAl

Joined Jun 17, 2014
9,778
Are you joking? Did you miss this part from OP: "but I dont know how to make theoretical analiysis". That right there tells me that they want us to do all the work. Anyone with the BSEE can just stop after reading that and go do something else. Because I have BSEE I am not going to try to cram 5 months of course work into this thread.

Hi,

"Are you joking?"

Yes, i am joking, for you. For the OP i am not joking.

JoeJester

Joined Apr 26, 2005
4,390
Bertus got the TS started with his link to the wiki about sziklai pair.

If the TS ever showed their work, a member here could help where the TS went astray ... even if it meant reviewing the ebooks here.

The problem is, when a originator wants the members to do all the work. It's not a problem for some, because they continually ignore the originator until something is produced. However, it is inevitable that a newer member will publish something that the originator will claim as their own. Then the newer member who answered will be rewarded with comments that they did not help the originator.

Some won't comment just to regurgitate what was already said by others. Neither MrAl nor shetii01 are newer members.

The threads in Homework Help has many who just answered the TS without seeing any work by the TS. I've yet to contrive a way to prevent those extra helpful members from posting complete answers. They are told to review the Rules, but choose not to follow them. Yes, this happens in every forum with a homework help section, not just AAC.

I know my crystal ball isn't up to ISO standards. Without the crystal ball, one can not determine how best to help the TS without documentation from the TS.

Sorry for this rant.

halil06

Joined Apr 9, 2017
3
First what is the purpose of
Hi,

What else would help everyone here to answer your question is if you showed some work. That way we know what approximations are allowed in your coursework at this stage in your education. Without that, we might throw the simplest to the most complicated analysis at you, either of which you might not like because it does not fit the coursework requirement at this time.
So if you show a little work about what you have done so far, that would help.
First what is the purpose of this circuit What benefits of negative feedback in this circuit ?

MrAl

Joined Jun 17, 2014
9,778
First what is the purpose of

First what is the purpose of this circuit What benefits of negative feedback in this circuit ?

Hi,

The purpose of this circuit is to amplify signals and provide a low output impedance to be able to drive a lower impedance load like a speaker.

One of the benefits of negative feedback is it reduces the gain to a point where the transistors can operate in a more linear way which keeps distortion (THD) down. Without that, the THD would be way high. It also keeps the gain lower (forced gain) so that as the transistor Beta's vary with current and temperature, the gain stays relatively constant.

In this circuit the feedback also sets the DC operating point which biases the transistors into their more linear operating region. That's just to get it working right in the first place.

halil06

Joined Apr 9, 2017
3
thank you vey much then how can I calculate the beta values for sziklai pairs for theoratical analysis I know they behaves just like an npn transistors but this time How can I obtain beta vallues for these transistors

MrAl

Joined Jun 17, 2014
9,778
Hi,

You have to get the Beta from the data sheet, or else test one yourself and compute the Beta possibly for several values of collector current.

Bordodynov

Joined May 20, 2015
3,036
beta values for sziklai pairs not need.
For example:

Bordodynov

Joined May 20, 2015
3,036
I advise you to define, what current you want to get through output transistors. I advise 50mA.
From reference given (datasheet) define the gain factor output transistor.
Consider the base current a transistor. This current approximately is a current collector before-output transistor.
See to scheme what assign the current through before-output transistors.
I have used the more complex scheme. In her easier to get on output half supplying voltages.