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THE "Universal" OP Amp

Discussion in 'Electronic Design' started by Trevor Morton, Mar 24, 2007.

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  1. Well, I've seem to have managed to confound another group. So, please
    excuse me for importing this thead.

    Instead of continually changing op amps, I am seeking to devise a
    single design suited to a wide range of applications. The desired
    criteria are as follows.

    4-12V power supply
    Bandwidth _DC_ through 20KHz
    DC coupled in and out
    Unity to 20 gain, variable by trimpot
    Low power DIP package
    Drive resistive load of 20 to 200 ohms,
    Output up to 2A, with Darlington follower
    Swing as close to rail as is practical

    At first, I thought such specs might be mutually exclusive in a fixed
    design. However, if there are such limitations, they seem to be
    receeding fast.

    For example, there is the "new" OPA569, rated at 2A. It meets my
    requirements except only operates up to 5.5V.

    http://focus.ti.com/docs/prod/folders/print/opa569.html

    Can someone explain, in theory or practice, why something like what I
    am looking for cannot (apparently) be achieved with a "standard" op
    amp and a couple of transistors? I am aware there are plenty such
    devices dediciated strictly to audio, but they do not fit the bill on
    several counts.

    I can imagine this would be of lasting value to thoses who lack the
    full range of engineering skills.

    Thank you for any input.

    Trevor Morton
     
  2. Robert Baer

    Robert Baer Guest

    Well, find an opamp that you like and will do everything except the
    drive. Then add the equivalent to the LH0002 (damn! been obsoleted) as a
    current buffer, giving a composite opamp with good drive capability.
    If you choose properly, the opamp can go to +/-18V supply (or 0/36V).
     
  3. Your "Universal" is false. It is a solution to your requirements,
    nothing "Universal" about it. So sit again on the specs of this circuit
    and watch out on conflictic definitions e.g. 12 volt/20ohm load/ low
    power package.
    ----> 144/20 = ~7W so where is the low power?

    HTH

    Stanislaw
     
  4. Eeyore

    Eeyore Guest

    As I've explained elsewhere, what you want is an *AMPLIFIER*. Your 'spec' is
    *NOT* an op-amp. An op-amp is typified for example by gain that's as high as
    possible typically 100,000 or greater at DC.

    When you get to understand the difference, the penny may finally drop.


    Graham
     
  5. Phil Allison

    Phil Allison Guest

    "Trevor Moron"


    ** The only thing "confounded" is you - Moron.

    Can't even get the simplest LM386 circuit to work.





    ........ Phil
     
  6. Genome

    Genome Guest

    Doesn't sound too universal to me..... Sounds like an amplifier that that
    needs desired criteria of......
    Apart from those who want a 'Universal Op-Amp' that does something
    different.
    That's OK....... (If you want to come across as a pretentious ****) Eeeyore
    will be along soon to not give you the design you thought you wanted in the
    first place........

    After someone else has told him how to do it and then he won't anyway.

    I think that's how it works.

    Bonza!

    DNA
     
  7. Eeyore

    Eeyore Guest

    My recommendation was a car audio amplifier chip.

    However the OP steadfastly refuses to usefully elaborate about his application.

    Graham
     
  8. Phil Allison

    Phil Allison Guest

    "EeysoreFuckwit "

    ** Will never work satisfactorily with a 4 volt supply.


    ** That is because he is a fucking TROLL and does not have one.




    ....... Phil
     
  9. Genome

    Genome Guest

    Here we go again......

    DNA
     
  10. Phil Allison

    Phil Allison Guest

    "Trevor Moron"

    ** How come you made no reply to this post ???

    --------------------------------------------------

    "Trevor Morton"
    ** Try again - you got it fouled up somehow.

    With a 4 volt supply, square wave drive and 33 ohm load ( no coupling cap),
    the output is a clean. 2.6 volt p-p square wave at *any* frequency up to
    20kHz.

    With a 12 volt supply, same set up as above, the output swing is 10 volt
    p-p.

    Same p-p swings apply to a sine wave input as well.
    BTW

    Make sure your input signal does not have a DC offset.

    ........ Phil

    ---------
    ----------------------------------------

    ** Cat got your tongue - fuckwit ?

    Meeeeoooowww



    ......... Phil
     
  11. Jamie

    Jamie Guest

    Really, i just received 50 LH0002 to replace a few bad one's in some old
    FENNER/CONTRX units. i think we paid around 2 bucks each.
     
  12. I think you can combine the closed loop bandwidth with the
    maximum gain and say that the opamp must have an open loop
    gain bandwidth product of at least 20*20k=400kHz. A little
    extra might not hurt. Lots of opamps have about a 5. to
    1MHz GBW product.
    (snip)

    How about 2 in an 8 pin DIP?
    Take a look at the LMC6482
    http://cache.national.com/ds/LM/LMC6482.pdf
    supply range 3 to 15 volts, rail-to-rail input and output,
    GBW=1.5 MHz (1 MHz with 3 volt supply).

    Add a complementary emitter follower made of high gain
    transistors like ZTX698B and ZTX788A
    http://www.zetex.com/3.0/pdf/ZTX688B.pdf
    http://www.zetex.com/3.0/pdf/ZTX788A.pdf

    And get a peak output current greater than 1 amp something
    like within a volt or so from each rail (more if you allow 2
    volts from rails).

    You will have cross over distortion, but you didn't spec that.

    For applications that don't need the high output current,
    eliminate the followers.
     
  13. mpm

    mpm Guest

    I am seeking to devise a single [op amp] design suited to a wide range
    of applications...

    You ever notice that when all you see are hammers, everything looks
    like a nail?

    -mpm
     

  14. That doesn't mean that they are not obsolete. I still have some NOS
    RTL and DTL ICs, but that doesn't mean that you could buy production
    quantities. Even Jameco is clearing out their remaining LH0002CN ICs.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  15. Ban

    Ban Guest

    To me it demonstrates only your disability to understand how an opamp
    functions.

    single supply
    GBW
    every opamp
    unity gain stable, but I want infinite gain
    ridiculous- trimpot
    somewhat outdated these days. Only for hobbyists
    I rather would like to be able to drive complex loads too.
    12V/20R= 600mA to me, not 2A. What about MOSFET output stage?
    Rail to Rail output
    You left out some very important data like PSRR, CMRR, common mode voltage
    range, input impedance, offset voltage, Bias current, noise, distortion,
    linearity, overload recovery etc.
    2A with only 150mV voltage drop. Can't be a darlington stage.
    Something like an LM386 already exists for eons.
    The industry doesn't produce parts for beginners like you only. Better you
    start understanding at least the most fundamental ideas behind opamps. Even
    a 741 is far more versatile than your data. You seem to have only audio and
    LED drivers in mind.
    I would say GIGO, my answer included. :-(
    Moron would be appropriate. There is s.e.b. for posts like this, where
    stupid questions do not exist.
     
  16. Robert Baer

    Robert Baer Guest

    ....maybe class D is in order?
     
  17. Robert Baer

    Robert Baer Guest

    DigiKey thinks it is obsolete.
     
  18. Fred Bloggs

    Fred Bloggs Guest

    Not nearly as pronounced as your *inability* to write in
    English-approaching a *disability* for sure.
     
  19. Ban

    Ban Guest

    what about your Italian?
    So don't take it too serious Fred.
     
  20. Fred Bloggs

    Fred Bloggs Guest

    I no speaka Italian...but then this is not an Italian newsgroup.
     
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