Amplifiers

Discussion in 'General Electronics Chat' started by Skeebopstop, Feb 8, 2009.

  1. Skeebopstop

    Thread Starter Active Member

    Jan 9, 2009
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    I am so used to using op-amps to do all my amplification, when would it be appropriate to actually do BJT etc.. transistor amplifiers?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    You might find such an animal useful when driving speakers and not earbuds. Op amps have a hard time handling +/- 75 VDC @ 12 amps.
     
  3. mik3

    Senior Member

    Feb 4, 2008
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    Op amps are more linear devices than BJTs and you can design easier. However, if you require high power outputs then you have to use transistors.

    What is the application?
     
  4. Skeebopstop

    Thread Starter Active Member

    Jan 9, 2009
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    Just inquiring for future design knowledge.

    So why not just op-amp into a buffer stage? i.e. emitter follower buffer etc..? Or a power push/pull?

    The component footprint of an op-amp amplifier seems like it would almost always be less, so easier to stick with op-amp and just buffer output.
     
  5. mik3

    Senior Member

    Feb 4, 2008
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    Yes, it would be better to amplify voltage using an op amp (if the voltage level permits) and then use a push-pull pair as buffer (amplify the current).
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    If possible, you should put the buffer inside the feedback loop. You will get better linearity (less distortion).
     
  7. Skeebopstop

    Thread Starter Active Member

    Jan 9, 2009
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    Aye, drives you through the cut-off regions. That is Class-AB yeah?
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    That seems to be the most popular choice.
     
  9. lespaul

    Active Member

    Jan 30, 2008
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    Most common high power amplifiers these days use an op-amp or BJT preamp section and a Mosfet output stage. I am currently touring with amplifiers that will drive 2500 watts into 4 ohms. The mosfet power stage is easy to bias and drives massive current with minimal distortion.
     
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