CA3240 Op Amp Question

Discussion in 'General Electronics Chat' started by Tom1962, Sep 28, 2012.

  1. Tom1962

    Thread Starter New Member

    Sep 10, 2012
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    I am going to use this op amp CA3240 as a voltage follow, see data sheet below. I was planning to use this in a 5 volt circuit -- i.e., so the chip is powered with 5 volts. When use it as a voltage follower, is there any harm if the input exceeds 5 volts? I assume the output will just be limited to 5 (or almost 5) and the op amp will otherwise be fine. Right?


    http://users.rowan.edu/~jahan/ECT/ECT_2007/presentations/324-opamp.pdf
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    yes no probs, you can input upto 8v over the supply .These are superb ics, i use them all the time.
     
  3. Tom1962

    Thread Starter New Member

    Sep 10, 2012
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    Ok thanks, but just testing on the breadboard it seems that the output of the voltage follower can only go up as high as the voltage powering the chip, less two volts. In other words, if I power the chip with 5v, then the voltage follower only works up to about 3 volts. (My follower has the input going into pin 3, with pins 1 and 2 connected to form the output.)
     
  4. t06afre

    AAC Fanatic!

    May 11, 2009
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    About 3 volt out then supply voltage is 5 volt. Is according to the datasheet. If you need higher output voltage you may change to a so-called rail to rail opamp.
     
  5. Tom1962

    Thread Starter New Member

    Sep 10, 2012
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    Not sure I understand what you are saying. If I power the chip with 12 volts, then I can use it as a voltage follower for a signal that ranges from 0 to 5 volts. Right?
     
  6. t06afre

    AAC Fanatic!

    May 11, 2009
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    Yes that is correct. The maximum output voltage is the supply voltage minus about 2 volt, in theory. So by using 12 volt as supply voltage. You should get 5 volt out with no prolem
     
  7. Tom1962

    Thread Starter New Member

    Sep 10, 2012
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    And, just to confirm, if I connect pin 1 and 2, and feed the input signal into pin 3, the output voltage should be on pin 1 and 2 right? I see in the data sheet there is a schematic for a voltage follower with reisitors and capacitors. Do I need that circuit just to make a voltage follower?
     
  8. Audioguru

    New Member

    Dec 20, 2007
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    Page 6 of the datasheet explains that the input protection for the Cmos inputs requires the resistor. The capacitor prevents attenuation at high frequencies.
    Almost all other opamps do not need them because this is a very old weird opamp.
     
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