Need help : Designing Push-pull Amplifier

Discussion in 'General Electronics Chat' started by inoek, Aug 14, 2008.

  1. inoek

    Thread Starter New Member

    Aug 14, 2008
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    Hello, i am kinda new to electronic world so i kindly hope everyone help on this matter.
    As u can see in this picture below, i am trying to design push-pull amplifier using complementary transistor. The output that i desire are :
    1. Vout = -Vin (not exactly equal i think, but i am expecting some good accuracy).
    2. Iout = 1 ampere max.
    The problem that i am encountering is my transistor heat-up very fast and eventually got burned. I am desperately needed help on this, since i am trying to design simple potentiostat. Any suggestion anyone ? and thank a lot for your help.

    [​IMG][​IMG]
    [​IMG]
    [​IMG]
     
    Last edited: Aug 14, 2008
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    Quite a few problems with this circuit: You appear to be using an op-amp with no negative feedback and therefore it will have enormous gain, it's output will either be high or low but never in between. Nearly 1A flowing in the biasing circuit, apart from the wasted power there is no way the op-amp could drive it. No means of setting and maintaining quiescent current.

    The best thing to do is to look at and become familiar with working amplifier designs, there are plenty on the net. Understand what each stage does and how it does it.

    This may be of use: http://sound.westhost.com/project76.htm
     
    Last edited: Aug 14, 2008
  3. bertus

    Administrator

    Apr 5, 2008
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  4. Wendy

    Moderator

    Mar 24, 2008
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    This is a similar solution for a different problem.

    [​IMG]

    Check this thread out, and this thread deals exactly with what you're talking about.

    R4 and R5 are very low in value, just enough to push the transistors into slightly higher off values. Just remove the ground symbol, and you are pretty close to what you want.
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    The base-emitter voltages and the diode voltages are all different.
    The transistors need emitter resistors to reduce the differences and the diodes need an adjustable resistor in series to adjust the idle current.
    The diodes should be fastened to the heatsink of the output transistors for thermal tracking.

    Of course the output should have feedback to the inverting input.

    An opamp can drive 2k ohms, not 15 ohms.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    I'd missed the 15Ω, I'd interpreted it as KΩ. On my drawing R4 and R5 will compensate somewhat for the differential. The end result is dead space, but it is a lot smaller, and therefore easier for the op amp to compensate for.
     
  7. inoek

    Thread Starter New Member

    Aug 14, 2008
    6
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    Wow, quite a lot of response i get. Thanks a bunch guys, i'll look into it and will start building it, hopefully i'll get the result that i desire.
     
  8. iamspook

    Member

    Aug 6, 2008
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    0
    Another small point. If you use an op amp as a driver, then make sure that it is fast fast fast and you will get better results.
     
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