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Push-pull amplifier

  1. Nov 10, 2007 #1
    Hi,
    I need some help with a push pull design.
    As a project , I am doing a audio cross over. The problem I have is that I cannot find a way to drive enough current into the speakers.

    For one speaker, the input current is 0.02 [A] and after the push=pull amplifier, I need to be able the supply a 8 ohms / 3 W speaker or a current of 0.61 [A]. I dont know how to find the values for the resistors.

    I am using a NPN transistor 2N3904 and a PNP tansistor 2N3906.

    please can someone help me ?

    Thank you

    B.
     
    Last edited: Nov 10, 2007
  2. jcsd
  3. Nov 16, 2007 #2

    berkeman

    User Avatar

    Staff: Mentor

    You're going to need a lot bigger devices than the 2N3904/6 small-signal transistors, in order to get the 600mA output current. You will also have bias current flowing through the transistors in Class AB configuration, so the power dissipated by the output transistors will be a bit higher still:

    http://en.wikipedia.org/wiki/Electronic_amplifier

    You can start by looking for BJTs in TO-220 packages that you can heat sink -- that should get you close to the power levels you are shooting for.
     
  4. Nov 22, 2007 #3
    Thank you berkeman,

    Your suggestion were helpful. I got it right!
    B
     
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