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Linear DC voltage inverter

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Discussion in 'General Electronics Discussion' started by pyrohaz, Jan 4, 2013.

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  1. Jan 4, 2013 #1
    pyrohaz

    pyrohaz

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    Oct 28, 2012
    Hey guys, i'm designing a passive diode based VCA and I was wondering what I can use as a linear DC voltage inverter. As in, if the input goes up by 1v, the output goes down by 1v. In AC terms, this would just be an amplifier with a gain of -1. How can I achieve this?

    The power supply will be at 5v and it will need to be able to source/sink a minimum of 500uA.

    Thanks,
     
  2. Jan 4, 2013 #2
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    The classic way to do this is with an op-amp.

    With a 5V supply rail, the issue then becomes, how close to the supply rails do you need to get? This will be perhaps the major issue in selecting an op-amp.

    I'm presuming that the frequency is low, and that you don't want the output to go outside of 0-5V.
     
  3. Jan 4, 2013 #3
    pyrohaz

    pyrohaz

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    Oct 28, 2012
    Ok, generally as close as possible to rails, complementary outputs would be useful but if I have a buffer before the inverter, I can just tap off each.

    What kind of circuit am I looking at here? Can I use a standard single supply inverting amplifier without a capacitor on the input?
     
  4. Jan 4, 2013 #4
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Assuming you get something capable of rail to rail inputs and outputs, you bias the non-inverting input to Vcc/2 using a pair of resistors (R3 and R4). Then you make a standard inverting amplifier with Feedback resistor R1 and input resistor R2.

    R1 = R2, and R3 = R4 = 2*R2

    The values of R3 and R4 are not hugely important, but keeping them at twice the value of R2 is optimal (I think).
     
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