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Help with amplifier output!

Discussion in 'Electronic Design' started by Himlam8484, Apr 5, 2007.

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  1. Himlam8484

    Himlam8484 Guest

    Hi people,

    I make a amplifier circuit. In my design, i connect some transistors
    ( type PNP) to increase the current output by connecting all of them
    common base, Emitter to vcc( all transistors were droven by another
    transistor). The current output is ok, but the signal output
    reversed the phase. I would like to take a signal with the same phase
    with input signal.

    Can anyone know how to connect transistor together to increase the
    current, but not change the phase?

    I am looking forward hearing from people,

    Lam
     
  2. Bob

    Bob Guest

    If you want current gain and no phase inversion, with one stage of
    transistors, then you'll need "common collector" configuration.

    For your PNP devices, hook the collectors to your minus supply. Tie the
    bases together. Each emitter will need a separate small resistor (to insure
    that the current shares equally), and tie the other end of all the resistors
    together. This will be your output.

    The problem with this simple configuration is that you can only provide
    (sink) current from your minus supply. You have two options for being able
    to also source current from your positive supply -- add a (high power)
    resistor from the emitter resistors to the positive supply, or add another
    group of NPN devices, in a similar configuration as your PNPs, with their
    collectors to the positive supply.

    The (high power) resistor approach will force you to run the amplifier in
    what's called "class A" operation. The latter approach can be run "class B"
    , "class AB", or "class A".

    You should research the available literature describing high power amplifier
    configurations and design.

    Bob
     
  3. Himlam8484

    Himlam8484 Guest

    Hi Bob,

    First, thank you for your reply. I forgot to tell you that i added
    another
    group of NPN devices. Now i will remake it following your idea. If
    having any problems, may you help me again?

    Thanks,
    Lam
     
  4. Himlam8484

    Himlam8484 Guest

    Hello Bob,

    with your descriptions, I do not need to change 2 driver transistors.
    I only have to change groups of NPN or PNP. Now, for NPN group i can
    use a PNP to drive or not? Can you tell me this?

    Thanks
    Lam
     
  5. Eeyore

    Eeyore Guest

    Emitter follower.

    Who's your lecturer / tutor btw ?

    Graham
     
  6. Eeyore

    Eeyore Guest

    What you really want is a complementary emitter follower. Google can help you.

    Graham
     
  7. Eeyore

    Eeyore Guest

    Google complementary emitter follower darlington output stage.

    Graham
     
  8. Himlam8484

    Himlam8484 Guest

    Hi,

    I know the google can help me. On the other hand, I know this
    knowledge from my Professor. But i would like to ask people to know If
    the people get new types or not.

    Thanks for your reply,

    Lam
     
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