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Voltage follower

Discussion in 'General Electronics Chat' started by cupidsd, Mar 6, 2012.

  1. cupidsd

    Thread Starter New Member

    Oct 16, 2011
    hi all,

    I am trying to design a voltage follower circuit. The input is quite low, around 0.8 - 0.9V.

    I tried an OP, whose power supply is +/-16V, then connected the output with inverting-input, and connected the non-inverting-input with my input (0.8 - 0.9V). But the output does not follow the input, and actually the output is around 1.4+V.

    The circuit does not work well. I guess it is due to the input is too low. Am I right? So what OP should I use then? Any comment is welcome.

    Thanks a lot.
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
    What kind of op amp did you use? Did you connect 100nF bypass caps from each power supply pin to ground? if you didn't, the op amp may oscillate, and the output could be pretty much unrelated to the input. (I'm assuming that OP is your abbreviation for op amp.)
  3. cupidsd

    Thread Starter New Member

    Oct 16, 2011
    Thanks for your reply.

    yes, OP is operational amplifier.

    Actually, Im using TL082. Since my power supply cannot deliver the output of 36V (=18V-(-18V)), I set the output to be 32V, which is quite close to 36V.

    I did not use any bypass capacitors, I will try tomorrow. Thanks for your advice.
  4. crutschow


    Mar 14, 2008
    Sounds like you are using only one power supply(?). Then you do not have a dual ±16V supply, you have a single 32V supply. There is a difference. It's a ±16V supply only if you have the center grounded. The power supply must have its ground reference tied to your circuit and signal ground. An op amp will not operate properly with a floating power supply.

    If you only have one supply then you need to use a rail-to-rail type op amp or provide a pseudo ground at 1/2 the supply voltage.

    Edit: And why are you trying to get to 36V? You do not want to operate at the op amps maximum voltage rating. Most op amps are operated at ±15V or less.