op amp rail voltages

Discussion in 'General Electronics Chat' started by jrevard, Jan 6, 2014.

  1. jrevard

    Thread Starter New Member

    Jan 6, 2014
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    hi, how can I create the rail voltages for an op amp? the (+) voltage seems simple enough but I'm not sure how to supply the (-) voltage... I am seeing that for working with a DC signal the (-) terminal can be connected to ground but what about for AC signals?

    thx
     
  2. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Depends on AC signal.

    If AC is centered on zero, then your AC signal is from -X to +X volts. So you need to provide a negative rail.

    If AC is centered on some positive value and the range of AC is, for example, from +1 to +5, then you don't need negative rail, just connect it to ground.
     
  3. #12

    Expert

    Nov 30, 2010
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    Build a power supply to create a negative voltage and connect that to the (-) supply terminal of the op-amp.
     
  4. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Using only a positive supply, if your AC signal is centered around 0 volts you can also deal with that by biasing the op amp's input at 1/2 the supply voltage using 2 resistors and coupling the input signal thru a capacitor.
     
  5. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    If you don't need anything outrageous, you can use computer power supply, they usually have a couple negative voltages.
     
  6. #12

    Expert

    Nov 30, 2010
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    or a 9 volt battery if you're just experimenting for a while.
     
  7. Brownout

    Well-Known Member

    Jan 10, 2012
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    If you have two power supplies, you can connect them in series and use the wire between the two as 0V, or ground. They you'll have rails for + and -.
     
  8. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Someone posted a pic of such setup a couple of months? ago. I tried to find it, but no luck.
     
  9. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    It was posted on these forums, but I found it with Google.

    Connect -9 volts from the battery to the negative rail of the op amp. Connect +9 volts from the battery to the positive rail of the op amp. Connect the ground from the batteries to the circuit ground.
     
  10. WBahn

    Moderator

    Mar 31, 2012
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    The claim that you can connect the negative rail to ground if you are working with DC signals isn't a valid statement. As with AC signals, if the input and output signals are compatible with grounding the negative rail, then you can ground the negative rail. If they aren't compatible with a grounded negative rail, then you can't.
     
  11. jrevard

    Thread Starter New Member

    Jan 6, 2014
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    Awesome, you guys are great
     
  12. w2aew

    Member

    Jan 3, 2012
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