Differential amplifier 0 to 5v signal input with -10 to +10v output

Discussion in 'General Electronics Chat' started by cj9, Nov 23, 2011.

  1. cj9

    Thread Starter New Member

    Nov 23, 2011
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    0
    Hi,

    I'm trying to drive a galvanometer which needs a differential input. It's not well documented (galvo board), but I tried driving it with a differential input from a DRV134, which doesn't work properly. The output of the
    I can't work out what's going on.

    Instead I'm hoping to use an op amp to drive it by putting -10 to 10v on the +ve pin and tying the -ve pin to ground.

    The only problem is that I can't find a working circuit anywhere that uses an op amp to convert 0-5v to -10-10v, could anyone help me with this please?

    Thanks for your time.
     
  2. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    For DC: by using two op amps from the same input, one that is non-inverting and one that is inverting, both with a gain of 2; then the output of one will go from 0 to +10V while the other goes from 0 to -10V.

    If you are dealing with a high enough AC frequency (audio), by cap coupling the 0V-5V input to an op amp it will become +/- 2.5V; with a gain of 4 the output will be +/-10V.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    I did this schematic for someone awhile back.

    It converts 0v to +5v, to -5v to +5v; and has both non-inverting and inverting output.
    It depends on +V being 10v, as R1 and R2 are summed to be 5v; and that is summed with the feedback resistor R3.

    You could change U1b to a noninverting configuration with a gain of 2 to get your desired output.
     
  4. cj9

    Thread Starter New Member

    Nov 23, 2011
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    Thank you for the schematic, it's very helpful. I'll build it up and see if it works!

    Just a quick question - what's the selection switch for?
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    As shown, the selector switch connects the galvanometer to the noninverting output.
    If it were at the other position, the inverting output would be connected; the red trace would then be at 5v when the input was 0v, and -5v when the input was at 5v.
     
  6. cj9

    Thread Starter New Member

    Nov 23, 2011
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    I see. I have some LM324s on hand, they are designed to "eliminate the need for dual rail power supplies". This means they have ground rather than -ve voltage input. Could you tell me if this circuit can utilise the LM324? It would be helpful as they have 4 amps in each chip. Thanks!
     
  7. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    If you eliminate the negative supply by replacing it with ground then the op-amp output can't swing below ground. You need a ±10V swing.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    You can use the LM324, but you must have dual rails; at least ±13v.
     
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