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op amp inputs

Discussion in 'Electronic Basics' started by gearhead, Aug 31, 2007.

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  1. gearhead

    gearhead Guest

    for example, LM324
    http://www.st.com/stonline/books/pdf/docs/4797.pdf
    the data sheet states a differential voltage of as much as 32 volts is
    permissible.
    But in the diagram it looks like at about 15 or 20 volts input
    differential the b/e junctions on one of the inputs would go into
    reverse conduction.
    Do I misunderstand or do they use protection circuitry not shown in
    the diagram.
     
  2. Guest

    Read all the info. You'll see note 1 "Neither of the input voltages
    must exceed the magnitude of Vcc+ and Vcc-"

    Are you referring to the diodes from both inputs to the power supply
    rails? Those would certainly be the 'limiting' factor.

    GG
     
  3. I think the PNP input transistors have been doped to produce
    base emitter reverse break down voltage exceeding the
    maximum supply voltage rating. This compromise reduces the
    performance possible with these transistors, but makes using
    this opamp with open loop inputs, very easy.
     
  4. Jamie wrote:
    ..
    ....Including all sorts of DC and low frequency (not audio)
    signal applications, and audio if you can arrange the load
    to keep only one side of the output totem pole conducting
    throughout the waveform (or if distortion is not very
    important, like alarm buzzers or telephone quality voice).
     
  5. Jamie

    Jamie Guest

    And also, if I remember correctly, the LM324 is one of those op-amps
    that has a discontinued output. meaning, when the follower outputs
    cross the zero path or near it, there is no minimum bias for both rails
    being applied to maintain constant current. In a way, this is good in
    equipment that wants to save on energy when it's used in things like
    OSC's, voltage comparator etc..
     
  6. Eeyore

    Eeyore Guest

    You mean 'do the input transistors' b-e junctions go into avalanche breakdown' ?

    It's always puzzled me too.

    You'd probably need to ask an analog IC designer.

    Graham
     
  7. Eeyore

    Eeyore Guest

    More use of weird and wacky nomenclature from Jamie the Clueless.

    Did you mean 'the output stage has zero quiescent current' ? In which case I
    believe the answer is yes, or 'close to zero'.

    I fail to see why you introduced this, since it has nothing to do with the OP's
    question.

    Graham
     
  8. Jamie

    Jamie Guest

    Ok idiot, Most people that come here and read are entry level or minor
    techs, they don't need to see the book thrown at them. What a jerk you
    are.
    Let me tell you something, I put my son through Electronic Engineering
    College.
    My son is a very intelligent kid how ever, having instructors
    throwing the lingo at him like that when he is really trying to get a
    grasp on
    what the instructor is trying to convey made it hard. Not just him but
    many other of his class mates.

    I helped him a lot in conveying the terminology into terms that he
    could understand. He then past that over to his class mates which also
    helped. I can say that he graduated with high oners (4.5) average.

    He got into the habit of taking down lots of notes in this class and
    I had to do a sit down with him at least 2 times a week.

    That's not bad for a kid that is dyslexic.

    So, you can use all the text book terms you want. I know what they are
    and choose not to use them here. I know those that are interested
    to learn about the subject are also eager to engage, its a pity idiots
    like you have to spoil it with your commentary.

    There are a few here I have a lot of respect for. That is only because
    they do know what they're doing and I noticed they only speak up towards
    people like you and help others that are trying to understand in the
    various ways of examples they offer to convey the answer. They normally
    don't leave with an insulting remark to alienate them.

    Sure doesn't sound like you does it ?
     
  9. Eeyore

    Eeyore Guest

    Yet that is exactly what YOU do.

    My answers are normally short and succinct and keep to topic, whereas yours are
    rambling, off-topic and full of errors including 'using the wrong words'.

    Graham
     
  10. Jamie

    Jamie Guest

    Yes, I remember years ago when I run into a problem with a 324
    going into oscillation in a particular circuit we were adapting
    from another op-amp type. the oscillation was only aprox .2 Pk-PK volts.
    using a feed back cap stopped that how ever, it also added to the
    miller effect problems. I think what we ended up doing was offsetting
    the + input via a pot and placing a (-) load on the output to force
    the OP-amp to correct. We only needed a 0..5 volt output on this OP.
     
  11. John Larkin

    John Larkin Guest

    He's been sinking into snarling-mad-dog, insult everybody, Roy L Fuchs
    mode for some time now. Just another sad insult-bot usenut.

    John
     
  12. Eeyore

    Eeyore Guest

    How big of you !

    I learnt a huge amount of electronic knowledge even before I went to Uni/college. Nor
    did I have anyone to 'put me through' either.

    That's because many university lecturers are clueless idiots who are totally divorced
    from the real world and real world ways of doing things. I had the same problem at
    UCL.

    There is however no excuse not to know what 'quiesent current' means since it's a
    very widely used term to describe a very important issue. Instead you rambled on
    about ......

    " a discontinued output. meaning, when the follower outputs cross the zero path or
    near it, there is no minimum bias for both rails
    being applied to maintain constant current. In a way, this is good in equipment that
    wants to save on energy when it's used in things like OSC's, voltage comparator etc..
    "

    Which is a perfect example of the very thing you were criticising. It also makes no
    damn sense.

    Graham
     
  13. Eeyore

    Eeyore Guest

    Miller effect in an op-amp circuit ?

    Once again, you're using technical terms in an inapproriate way.

    Graham
     
  14. Eeyore

    Eeyore Guest

    I suggest you read my posts HERE !

    I only snarl at ineducable American idiots.

    Jamie IS a clueless twat and posts idiotic nonsense that never answers the OP's
    questions.

    Graham
     
  15. gearhead

    gearhead Guest

    That makes sense.
     
  16. Jamie

    Jamie Guest

    Typical trash.
     
  17. Jamie

    Jamie Guest

    Hit the books trash.
     
  18. Jamie

    Jamie Guest

    go wipe your ass, you stink.
    btw, clean your keyboard afterwards. it's most likely full of brown
    residue and drool.
     
  19. Al in Dallas

    Al in Dallas Guest

    Why are you writing nasty invective to someone who is trying to help?
    You make it extremely difficult to believe your claims.
     
  20. Jamie

    Jamie Guest

    Ha, sorry, but you must be new.. stick around for a bit.
    you'll get the picture. When he's doing any replies to
    things I write, it's only to help him self.

    Maybe you haven't been here long enough.

    Have a good day.
     
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