power amplifier - class AB HELP

Discussion in 'Homework Help' started by yash_avengers, Sep 28, 2015.

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  1. yash_avengers

    Thread Starter New Member

    Sep 28, 2015
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    The requirements are a minimum of 8W RMS power to 8Ω speakers with a maximum of 1% second harmonic distortion and 0.2% third harmonic distortion. Single chip integrated IC amplifiers are not allowed. BJT and MOSFETs in class A, AB, D or circlotron topology are recommended.

    For the amplifier I tried building the EXACT circuit on this circuit. But apparently the signal got de-amplified instead of amplifying.http://hackaweek.com/hacks/?p=332

    I think I probably need to change my resistor, capacitor values but not sure what value exactly I should choose. ALso need to change the PNP and NPN transistor as well as I think that might be the reason I am not getting desired output.

    Can anyone help me in deciding what kind of set of resistors, capacitors, diodes and transistors I need as per my requirements?

    Mod edit: One thread is enough, keep it on the other thread in the homework section.
     
    Last edited by a moderator: Sep 28, 2015
  2. dannyf

    Well-Known Member

    Sep 13, 2015
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    That's a tiny amplifier and cannot deliver the kind of power you want, nor the performance.

    Look up a real amp instead. Bits are much easier to stablize
     
  3. yash_avengers

    Thread Starter New Member

    Sep 28, 2015
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    Do you have any specific recommendation for the circuit to deliver that kind of power? I couldn't see on that website!
     
  4. shteii01

    AAC Fanatic!

    Feb 19, 2010
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  5. Russmax

    Member

    Sep 3, 2015
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    Yash, the 1st step is to determine the voltages and currents that you will need to meet the 8W, 8ohm requirement. You will need to understand the relationships between RMS and peak voltage, and how that relates to the supply voltages you will need. You will also find the the amount of idle DC current in the output transistors has a large effect on the distortion.

    If you do the class AB amplifier you've picked, you will find that particular circuit is not well designed, and you will be lucky if it works at all. It is also a difficult load for your signal source to drive. You will need a circuit with nearly equal input and output voltages, so you can apply feedback to help control non-linearities. Keep researching to find a better circuit. If this is a class assignment, I bet the textbook is a good place to start. If not, look up Douglas Self for a complete approach to designing AB amplifiers with low distortion. He has books, but also a lot of online materials:

    http://www.douglas-self.com/ampins/dipa/dipa.htm

    The short version of my reply is that this project is very big, and this forum is inadequate for us to do much more to help you. You're not describing a simple homework problem, but a large project. Especially if you have to build it.

    Regards
     
  6. yash_avengers

    Thread Starter New Member

    Sep 28, 2015
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