split supply problem

Discussion in 'General Electronics Chat' started by philbowles2012, Aug 28, 2013.

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  1. philbowles2012

    Thread Starter New Member

    Mar 28, 2013
    I am trying to build a split supply for some op amp circuits. I came across this circuit http://www.instructables.com/file/F4XPE5WH3Z3UFPV

    I'm a bit of a n00b to all this and I simply don't "get" it at all.

    I tried it in a simulator and then built it. In both cases, I get the requisite +12/-12v, so what's the problem then?

    The problem is when I try to USE it! If I connect an led(+ 470R resistor) between 0 and +12V then the -ve side drops to -19 and the "+12" is now +5v. Any "load" on either side totally screws up the "balance"

    I have a theory...if it's right, I'll go "Eureka!" and carry on gradually learning electronics...if not, my head will probably explode and I will have to accept I have far more learning to do than I thought. Your help is therefore appreciated:

    I'm using a wall-wart, not a battery. I'm thinking that "-ve" here is genuine, earth-potential 0v and that the wart isn't "floating". This is sort of "confirmed" as it has a metal earth lead rather than a dummy plastic one.
    Also in my simulator, it won't run until at least something is at ground potential...hence same results in sim?

    Hmmm - i tried it with a "floating" supply (plastic earth pin) and a battery pack...my theory is wrong, my head now explodes as any "load" above the 0v rail causes major changes in values of + and - rails no matter the type of value of the input supply

    What am I missing?

  2. Wendy


    Mar 24, 2008
    This was neither feedback nor a suggestion, so I have moved it to a more appropriate forum.

    See if this helps.

    Creating a Virtual Power Supply Ground
  3. analogdesign

    New Member

    Aug 29, 2013
    What are you using for your ground reference? The voltages +12 and -12 only make sense when they are referred to some common voltage. When you measure them, where are you putting the ground lead of the multimeter? -19V and 5V indicate you are still getting 24 volts out of your supply. I think you need to establish a ground somewhere. Maybe measure the +/- 12 V relative to the zero volt output in your link?

    Good luck.
  4. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    The ground is referenced in the diagram as 0V.

    What you saw on your simulation is because the load wasn't balanced. Yes, my simulation produced similar results with a single load. If you use the same load on both sides, the voltages will return to + and - 12. Load imbalances will drive you crazy with this circuit. I didn't see the instructable on this circuit, but I wouldn't use this circuit except as the example it illustrates.

    I would take instructable's circuits with a grain of salt.

    If your looking to learn, use the ebooks here. There are also experiments for you to try.
    Last edited: Aug 29, 2013
  5. Wendy


    Mar 24, 2008
    The OP has another thread on the subject. I am therefore closing this one.
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