IC 741 amplifier circuit

Discussion in 'Analog & Mixed-Signal Design' started by vishal0312, Dec 23, 2016.

  1. vishal0312

    Thread Starter New Member

    Dec 23, 2016
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    i want to amplify 0 -20 milliVolt (DC) to 0-50 volt using Opamp IC 741 can anyone help me with circuit design.
     
  2. ericgibbs

    Moderator

    Jan 29, 2010
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    hi,
    The 741 is not specified for 50v operation.
    E
     
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  3. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    As said, you will never reach the 50 Volts:

    [​IMG]

    30 volts will be the max at ±20 Volts supply.

    Bertus
     
  4. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    The maximum supply voltage for the LM741 is ±22V so the maximum output voltage swing is about 40V.
     
  5. Sensacell

    Moderator

    Jun 19, 2012
    1,903
    574
    An opamp could be used to 'close the loop' around a secondary voltage amp with a 50 V output capability?
    Of course with the feedback attenuated to meet the opamp voltage limitations?

    Devil is in the details:

    What kind of gain and offset accuracy is required?
    What is the load?
    What bandwidth?
     
  6. vishal0312

    Thread Starter New Member

    Dec 23, 2016
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    sorry for my mistake it is 0 to 5 volts
     
  7. vishal0312

    Thread Starter New Member

    Dec 23, 2016
    4
    0
    sorry it is 0 to 5 volts i don't want to operate any load on that and it is 0 to 20 milli volt DC signal which i have to amplify
     
  8. vishal0312

    Thread Starter New Member

    Dec 23, 2016
    4
    0
    sorry it was a mistake i want to convert 0 to 5 volt from 0 to 20 milli volt DC signal
     
  9. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    Neither the input nor output can swing to the negative supply rail so you will need to use a split rail supply, say ±10V.
    Then you can connect your input to the non-inverting input and set the gain to 5V/20mV, or 250. For instance, from the inverting input connect a 1k resistor to 0V and a 249k resistor to the output.
     
  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    As said above, the 741 output cannot go all the way to the supply voltage. If you supply with -15 to +15 volts, it can only output a range of -14 to +14 (into a big value resistor like 10k and more). If you drop down the load to 1k or so, the output can only cover the range of -13 to +13. Worse as the load gets smaller - check the specs for max current.

    NOTE! The input offset voltage is 1 - 5 mV or, in your case 5 to 20% error. You will need to trim the OP amp. See DATASHEET for instructions.
     
  11. DickCappels

    Moderator

    Aug 21, 2008
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    You can use the circuit below. Keep R2 under 20k (arbitrary choice for bias current dependent low offset voltage).
    upload_2016-12-23_20-44-51.png
    Gain = 1 + (R2/R1)
    http://www.eecs.tufts.edu/~dsculley/tutorial/opamps/opamps2.html
    upload_2016-12-23_20-45-58.png
    Per GopherT use a 10K or 20K as shown above to adjust the offset and per AlbertHall remember to use + and - power supplies and you should be good to go.

    edit: Corrected AlbertHall's name.
     
    Last edited: Feb 16, 2017
  12. hp1729

    Well-Known Member

    Nov 23, 2015
    2,306
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    It can be done with power rails of +9 V and -9 V. The LM741 does not work well close to power rails. For a reliable +5 V out you need +V of about +9 V. With an input close to ground you need the negative power to be negative, not ground.
    Or use a better op amp.
    The LM741 is used in learning exercises because it has all the defects of a bad op amp. It is a good example of a bad example. :)
     
  13. crutschow

    Expert

    Mar 14, 2008
    19,543
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    Yes, it's very good for teaching op amp frequency response limits, input and output voltage limits with respect to the power supply voltage, the effect of amplifier offsets, etc.
    Truly a good bad-example. ;)
     
  14. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    Who he?
     
    panic mode and ErnieM like this.
  15. DickCappels

    Moderator

    Aug 21, 2008
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    Your twin brother?

    I am sorry for the error and have corrected it.
     
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