Selecting the correct op amps

Discussion in 'The Projects Forum' started by Will292956, Oct 20, 2013.

  1. Will292956

    Thread Starter New Member

    Oct 20, 2013
    3
    0
    Hey Guys,

    I'm working on a project the uses a Pololu Orangutan. I will be modifying a dc signal that is from 1-4 volts. The first will be a differential op amp that will cut of the bottom of the signal and the second will scale it up.

    I have no idea which op amps to purchase. I assume their power supply needs to be 5 volts and ground because I am using the orangutan.

    Thanks in advance.
     
  2. alexfreed

    Member

    Oct 8, 2012
    72
    10
    If both the input and output are within 1 to 4 volts (not quite clear what function you need) then a cheap lm358 should work. "Rail to rail" op amps are in most cases more expensive, but there are a few that are not for low voltage. For example MCP6002 is 39 cents at Jameco.
     
  3. Will292956

    Thread Starter New Member

    Oct 20, 2013
    3
    0
    Sorry, it is probably really anywhere from .25 to 4.5 for the inputs, so I think I will need rail to rail.
    The rate of change is very low (The max dc rate of change is probably only 4V/min).
    But for this application the op amp needs to be accurate as possible, and I wouldn't mind paying a few dollars/op amp if necessary.
     
  4. #12

    Expert

    Nov 30, 2010
    16,278
    6,790
    This is the one I know about.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The LMC6442 needs compensation if the gain is less than 2, otherwise it may become unstable. Also, the LMC6442 has a GBW in the KHz range; not that it's a "bad" opamp per se; if speed isn't an issue it will probably do fine.

    The MCP600x has an input offset of ~4.5mv, which will be amplified by the gain of the stage. Since we don't know what the desired gain is, or how much precision is required, the input offset may not be a big deal. Mouser sells those for $0.36/ea in single quantity.

    DC is the input; what's the desired output, exactly? What do you mean by "the bottom of the signal?"
     
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