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Class AB Amp Project
Class AB Amp Project
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Old 28th March 2004, 04:45 AM   #1
USFishin is offline USFishin  United States
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Default Class AB Amp Project

I am currently a EE student at the University of South Florida and I need to do a project in my Electronics II class. I am interested in audio and amplifiers so my friend and I decided to do a class AB amp. The only specs from the professor are as follows:

class AB amp outputting 1W into a 4 ohm speaker

I know this amp is a baby but I have never built an amp before and I am wondering if anyone has a schematic I can use for a class AB amp? Any suggestions, things to watch out for, etc. from anyone would be greatly appreciated.

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Old 28th March 2004, 07:17 AM   #2
subwo1 is offline subwo1  United States
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Well, to me you picked one of the most fun projects. I chose the same one and am glad I did. I think a student learns more if they feel their work is enjoyable. I am not even going to suggest any topologies. I recommend you try out almost any ideas you have and see how they work or don't work. The project is made more interesting by the fact that there are so many ways to build an amplifier.
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Old 28th March 2004, 03:19 PM   #3
fab is online now fab  Canada
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Class AB Amp Project
I suggest you begin with something simple that you fully understand before getting into complicated stuff. I have attached the project we had to do in one of my electronic course 16 years ago!

The op-amp in the input stage and the mosfet output stage simplify a lot the total number of components used.

Let us know which circuit you will use once you made up your mind!
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Old 28th March 2004, 06:29 PM   #4
sreten is offline sreten  United Kingdom
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Location: Brighton UK
Well I have to say fairly amusing.

Designing the amplifier and why its designed that way
is the problem, there is no simple or single solution.

TBH no-one would use class AB for 1W/ 4ohm,
in its standard power amplifier form, pure class A
is an easy choice here.

The problem is not what is appears.
You are being asked to provide a non-optimum solution,
how much you learn in the process is up to you.

For 1W / 4ohm there are better options than standard
class AB if you have voltage rail limitations, and here you
do, how much extra rail voltage above output swing do
you need ? Too much !

A standard AB output makes poor use of low voltage rails.
(Assuming a compound output pair)

Look up Analogue Devices AD820 and
investigate common emitter output stages,
which is the way to do it.

(Very common in battery powered equipment)

The theory may not be what you are used to !

Still class AB but rather different to standard topology.

The problem is actually far more difficult than a good 50W amplifier.

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