op amp recommendation

Discussion in 'General Electronics Chat' started by JingleJoe, Feb 2, 2012.

  1. JingleJoe

    Thread Starter Member

    Jul 23, 2011
    185
    10
    Can anyone recommend me a FET input op amp which can sense inputs down to the negative rail and has an output which can swing down to the negative rail too?

    I intend to use this amplifier with a single rail supply, so the "negative" voltage will be ground (0V). I am going to use it as a buffer/voltage follower in a sample and hold circuit (I have attached a simple diagram) This is why I require the high input impedance which a FET op amp has, however a standard transistor op amp would be fine if it has as high an input impedance as a FET op amp.

    Supply voltage = 12V
    Input = 40mV to 3V
     
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  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Most Jfet-input opamps have inputs that work up to the positive supply voltage but not near the negative supply voltage.

    Many years ago Texas Instruments made the TL091, TL092 and TL094 opamps that had inputs that could work down to the negative supply. It is not made anymore.
    I tried them but their slew rate was as low as a lousy old 741 opamp so they worked poorly above 9kHz.

    Today there are thousands of Rail-To-Rail Cmos opamps available. Their inputs and outputs go to both supply voltages.
     
  3. jaclement

    Active Member

    Apr 15, 2009
    34
    0
    Try the TLV271 ,272,or274. High input impedance, rail to rail input and output reasonably cheap 3volt to 16 volt power
     
  4. JingleJoe

    Thread Starter Member

    Jul 23, 2011
    185
    10
    Audioguru: Care to suggest some of those thousands of chips, specifically which you have found to be of low price and acceptable quality? By the way I'm happy with 741 slew rate as I will only be operating at about 5 Hz and lower, practically DC :p

    Jaclement: Sounds like just the thing I'm after, I will look them up now.



    Thankyou chaps :)
     
  5. JingleJoe

    Thread Starter Member

    Jul 23, 2011
    185
    10
    P.S. Looked them up and those TLV op amps look great! Thanks very much for the suggestion!
     
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