Op Amp Power Supply

Discussion in 'The Projects Forum' started by Benjii, Apr 22, 2013.

  1. Benjii

    Thread Starter New Member

    Apr 22, 2013
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    I am building a guitar effects pedal circuit, as part of this circuit I am using a LM358N op amp. Previously when I had created op amp circuits using multisim, I could place 2 batteries in, separated by a ground to give me a positive supply and a negative supply for the op amp. Shown in attached image.
    Is it possible to give a positive and negative supply to an op amp by using a single power supply? Would there be a way of reversing the polarity? (I only ask about reversing polarity as I think I had seen a circuit which supposedly did this on the internet somewhere, but can't remember where)
    I think I need the positive and negative supplies as I need the full audio signal, I wanted to be able to supply it from 1 battery however.
    Hopefully someone can help me here.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Here's a reference on powering an op amp from a single supply.
     
  3. Benjii

    Thread Starter New Member

    Apr 22, 2013
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    I checked on the datasheet for my LM358N and it does require me to have VCC+ and VCC- not VCC+ and GND
    If I use the method for connecting a voltage into the + input of the op amp, will that affect the rest of my circuit?
     
  4. crutschow

    Expert

    Mar 14, 2008
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    Don't understand your question. :confused: What is "the method" and "the + input" that you are referring to?

    You can use a Vcc+ and GND if your output signal always stays positive.
     
  5. Benjii

    Thread Starter New Member

    Apr 22, 2013
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    I am referring to the document you originally referred me to, did you look at it?
    I checked the datasheet for the LM358N and it requires a negative supply. Also due to the fact that it is an audio signal I am amplifying, it will not always stay positive.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    Yes, I've looked at it. Didn't know that was what you were referring to. :rolleyes:

    It will affect your circuit to the extent that the capacitors will block any DC portion of the signal. It will only amplify the AC portion.

    If you look at this datasheet for the LM358 you will see that it says
    "Wide Power Supply Range: DESCRIPTION
    – Single Supply: 3V to 32V
    on the first page.
     
  7. patricktoday

    Member

    Feb 12, 2013
    157
    42
    Here's a single supply circuit that will center your input signal around the halfway point of your supply voltage:
    http://images.elektroda.net/86_1216409204.jpg

    If you don't use a split supply you have to use a voltage divider to bias your signal. It's ok to use a single supply on an op amp, though; it doesn't know the difference only that the negative supply is lower than the positive supply by an adequate amount to power the op amp.
     
  8. wayneh

    Expert

    Sep 9, 2010
    12,100
    3,036
    +1
    Don't get hung up on the semantics of "dual" versus "single" supplies. There really is no such thing as a dual supply for an op-amp (I'm sure someone will object to that sweeping statement), there is just ∆V across the power pins. The rest is all about how the inputs are biased. Sometimes it's a great convenience to have that center "ground", virtual or not, and sometimes you don't care.
     
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