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Buffer circuits?

Discussion in 'Electronic Basics' started by Ron J, Dec 19, 2005.

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  1. Ron J

    Ron J Guest

    All,

    Merry Christmas and a Happy New Year!

    I was looking through some sensors on Digikey. Some of the ratings are
    given at a certain load. For instance, 50 mV at 1 k-ohm. If I wanted to
    bump this voltage a bit higher, can I use the following op amp buffer
    ckt?

    The sensor output is connected to 1 k-ohm resistor with one resistor
    terminal connected to the non-inverting op amp input and the other
    terminal is grounded. The opamp output is looped back to the inverting
    input using a low loss piece of wire. The opamp output is then
    connected to my measurement device.

    Will this type of circuit work accurately with little deviation from
    the original voltage input at the opamp?

    I was thinking of all the losses that is encountered from the input of
    the opamp to its output. My main concern is that since the output
    deviation of the sensor only goes up to 50 mV at 1k-ohm, then noise
    might affect it significantly compared to a higher output voltage,
    right?

    Thanks!
     
  2. Well, you said you wanted some gain, so why not use a 10 k ohm feedback
    resistor instead of a piece of wire? That would give you a voltage gain of
    10. The non-inverting op-amp input is often grounded through a resistance
    equal to the parallel equivalent of the input and feedback resistors (to
    minimize offset error).
     
  3. I should have mentioned that the signal is fed to the inverting input with a
    1 k ohm resistor.
     
  4. Jasen Betts

    Jasen Betts Guest

    Yes. at low frequencies (DC to about 1KHz is excellent) higher frequencies
    depend on the op-amp.
    yes. you can get some gain from that buffer circuit by using a 1K resistor
    from the inverting input to ground an a 10K from the output to the inverting
    input

    That'll amplify the input 11 times so your signal is 550mV want more?
    increase the 10K.
     
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