alternative AD521 op amp

Discussion in 'General Electronics Chat' started by greens, Mar 13, 2008.

  1. greens

    Thread Starter New Member

    Jan 31, 2008
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    If you don't have a AD521 op amp what can you use in place of it?
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    What other opamps are in your inventory to choose from?

    hgmjr
     
  3. hgmjr

    Moderator

    Jan 28, 2005
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    The AD521 is an instrumentation amplifier and so if you are to have a chance of coming close to an alternate you will need to use three high-quality conventional opamps.

    hgmjr
     
  4. greens

    Thread Starter New Member

    Jan 31, 2008
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    this is a question that i have on my homework this is what it says word for word...
    "If you could not find a AD521 Op Amp what would be an alternative IC?"
     
  5. hgmjr

    Moderator

    Jan 28, 2005
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    What other opamps have you studied in class?

    It may turn out that the answer is along the lines I have already indicated. That being that you would need to use three conventional opamps to mimic the AD521 instrumentation amplifier.

    hgmjr
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    Every semiconductor manufacturer makes instrumentation amplifier ICs. Look at the spec's of the one to be replaced and look at the hundreds of others to choose from.
     
  7. greens

    Thread Starter New Member

    Jan 31, 2008
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    we've studied 741, 3140,725 and 748. but mainly 741.
     
  8. hgmjr

    Moderator

    Jan 28, 2005
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    It's true that other semiconductor manufacturers make Instrumentation Amplifiers.

    Here is a Burr-Brown Instrumentation Amplifier for example. You will need to compare the specs to be sure it had the same or better performance than the AD521.

    hgmjr
     
  9. greens

    Thread Starter New Member

    Jan 31, 2008
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    ok sounds good. Thanks for your help! both of you.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    I suggest that you do a LOT of research on instrumentation amplifiers, and find at least a couple of alternatives that ARE instrumentation amplifiers.

    I'm not a professor, but if I were and someone came in my class suggesting that op amps could be used instead, I'd give them an F.

    While the assertion that individual op amps can be used as instrumentation amplifiers is true, it is cost prohibitive, PCB-real-estate hogging and extremely labor intensive from a manufactureability/maintainability/reliability point of view. You might as well recommend building an LM317 voltage regulator IC from discrete components.

    Instrumentation amplifiers have their resistors laser-trimmed at the factory, and have guaranteed CMRR. You really can't hope to even get close to that with discrete op amps unless you spend some time "tweaking" each amp - and that means pots, and that means expense and parts that will go out of alignment.

    But to understand the kind of answer your professor wants to hear, you should know something of their background. If they have any background in manufacturing whatsoever, they will expect a substitute instrumentation amplifier that is a pin-compatible plug-in replacement.

    Along with a backup source.

    If their background is purely acadamia, they'll likely expect exacting specifications for an equivalent op-amp circuit, including tolerances for all components.

    Even 0.1% resistors aren't good enough to ensure sufficient CMRR in many cases.
     
  11. DC_Kid

    Distinguished Member

    Feb 25, 2008
    638
    9
    this looks similar
    http://focus.ti.com/docs/prod/folders/print/ina114.html

    perhaps teacher just wondering if you know the basics, such as capable gain, CMRR, etc. but the like sgt. wookie says, perhaps teacher wants to know if you know the series well so that your choice is pin/pin compatible....
     
  12. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    Greetings green,

    I do hope you will let us know what answer your instructor expected to receive for this question once you know for sure.

    hgmjr
     
  13. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    That course material may need a bit of updating. All the devices covered are quite obsolete.
     
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