deciding on single rail or dual rail op amps?

Discussion in 'General Electronics Chat' started by rick5, Apr 21, 2009.

  1. rick5

    Thread Starter Member

    Jul 17, 2008
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    I'm designing an audio circuit and have to choose whether to go for a single rail or balanced supply IC.

    For single rail op amps are there any available that internally create a negative rail with a kind of built in switching regulator, so even though the designer has only a 9V battery to play with you can still get an output that swings above and below the earth rail?

    If not I guess for single rail op amps in audio circuits, you have to level shift the resulting output back to a zero offset - or you have a kind of level shift distortion.
     
  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
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    In my experience, I have not come across a single rail opamp with a built in switching regulator. It might be out there.

    Level shifting can be as simple as adding a capacitor in series with the output load. Be sure to select parts that give you the output frequency response that you desire.

    Remember, you do not have a negative supply so you can not add an opamp or resistor network to shift the levels down to zero.
     
  3. rick5

    Thread Starter Member

    Jul 17, 2008
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    Come to think of it that's actually not a bad idea for an IC. An op amp with a built in inverting switching regulator, where the user only has to supply external capacitors for a charge pump.

    I take your point about level shifting, that's what I was thinking, I don't want to unwittingly create a first order filter that messes up my frequency response. I'm not sure how else to do it though, unless I go the balanced supply route and use something like the MC34063A to get the -ve rail.
     
  4. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
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    Look at the LM386, which is a low voltage audio amplifier that has been made by National Semiconductor for years. They used to be available even through Radio Shack. The data sheet, http://www.national.com/ds/LM/LM386.pdf, shows the output being driven through a 250 uF capacitor to an 8 ohm speaker. It is worth a look. It will run off of a 9 volt battery as well.

    It might not be exactly what you are looking for but it may help you make your final decision.

    Creating a dual supply is definitely another solution to the design; however, it involves a large number of parts and power consumption that you may be able to do without, especially for battery operation.
     
  5. peranders

    Well-Known Member

    May 21, 2007
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    Rick, if you want a simple solution you should choose two batteries but it's quite simple to use a single supply also. What is your application?
     
  6. Wendy

    Moderator

    Mar 24, 2008
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  7. rick5

    Thread Starter Member

    Jul 17, 2008
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    Well, actually I was reading that just before you made this reply!

    You're right, a simply virtual power supply ground is a good idea and probably what the last poster was hinting at also instead of an inverting switching regulator. He also suggested using 2 batteries, that's actually quite a good idea . All my breadboarding has been with 2 batteries just for convenient split rail setup, but for some reason I didn't think of that for the production version due to brain fade. I've got the solution right infront of me already.

    I like your split rail ideas though Bill, that thing with the complementary BJTs some diodes & resistors, that looks pretty good.
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    For protoboarding I regularly use two 9V batteries. Single supplies are simplier though.
     
  9. Stevezachtech

    New Member

    Apr 21, 2009
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    The simpler the better I always say, I totally agree 2 batteries are much simpler to utilize.
     
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