How to make a simple negative power supply

Question

I want to experiment with amplifiers but I need a negative power voltage source.

I looked for some circuits but as far as I found they either are not simple & reliable or require an IC.

Is there any simple way to get negative power supply without using a railsplitter IC or AC power source?

Also I read about these 'virtual grounds' but I couldn't figure it out. Is it like ; we choose a positive voltage point as ground so technically the real ground is more negative relative to positive point we chose?

This one works well but needs an AC power supply and high capacity and voltage capacitors and they take a lot of space but so far best I could find.

This one looks simpler and doesn't need an AC source or big capacitors but either I can't understand how it works or it doesn't work that well.

Edit: If what I want is not possible, can you recommend some ICs for it? I can order them from abroad because they're not common in my country and this why I asked about circuits that don't involve them in the first place.

Edit I think I was not clear about what I want:

I specifically don't want a circuit which requires an AC power supply because yes I know it's so easy to make a circuit like that.

Answer 1

I believe that this is by far the simplest way to get negative voltage, if you can simply use two batteries in series and treat the mid point as GND. then the + side of the 1st cell will be your positive rail and the - side of the 2nd cell will be your negative rail.

Answer 2

The little rail splitter circuit with two resistors and 2 capacitors is a poor design:

^{simulate this circuit – Schematic created using CircuitLab}

With R1 and R2 equal, you have a resistor divider which gets you a potential half-way between its top and bottom potentials. C1 and C2 simply try to keep that voltage steady as the power supply wobbles up and down slightly, but asside from that, they aren't much help.

The problem is that any current being drawn via R1 or R2, due to things connected to that mid-point (for example, Rload in the circuit on the right), will cause the center potential to to deviate from the required half-way value, so you have to be super careful not to "load" it in any way. Even worse, as the load varies (and it probably will), the mid-point potential varies with it.

This is a reasonably good starting point though, because at least you get a nice 6V reference potential, that you can use to create a stronger, more robust 6V supply point. You can do this with a single opamp, connected as a voltage follower:

^{simulate this circuit}

The opamp input draws no current from the divider, so you needn't worry about it ever loading and upsetting the +6V reference. It uses negative feedback to counter any influence that a load presents at its output, to maintain a steady 6V there even under modest load.

You can power this circuit from any DC source over 4V or so, reassign your ground point, and re-label the supply rails to more meaningful names. For example:

^{simulate this circuit}

This will work quite well as long as you don't ask for more than about 10mA from the opamp (sinking or sourcing). More than that and you'll need a beefier solution.

Also, beware the dreaded ground loop. If your source of DC power is not isolated from mains Earth, you must not connect your new ground point to that same Earth, because it has a different potential.

Answer 3

You could try using a MAX1044/ICL7660.

This is a DC-DC converter I use for bipolar PSUs in audio circuits sometimes. You can use a 9V wall wart or battery to get a -9V output for example. Just make sure to filter it enough and connect the "Boost" if you're working with audio frequencies. The boost will bring the switching frequency above the audio band so you don't hear that noise.

There are some example schematics in the datasheet you might find useful. I often use the one from Figure 6 on page 8.

Hope this helps!

Answer 4

One solution is to use two "wall wart" (or other) DC power supplies, and connect the positive terminal of one supply to the negative terminal of the other, and call that "Ground/Zero volts". The free positive and negative terminals are your bipolar supply.

This will work with the typical "wall wart" supply, as their outputs are "floating" - neither side is connected to any "Ground". Caution may be required with other sorts of supply, as their negative terminal may be connected to a metal case, and thence to "Safety Ground/Earth Ground".

Another solution would be to use an isolated DC-DC converter - connect its positive output to the negative terminal of your main supply, then its negative terminal is your negative supply. Some DC-DC converters are not isolated (their input and output ground terminals are connected) so cannot be used here.

Answer 5

You could get ahold of an old ATX power supply, which has -12V on pin 14.

That's probably your cheapest and easiest route if you don't care about the noise from a switching supply. You'll need to add a dummy load to get it to start up most likely (google for details, there are a number of folks using these for a poor man's bench supply ). I really can't condone getting inside where the 400V mains-derived voltages live, but some do it, and many, I assume, live to tell the tale.

Once you have +/-12V you can regulate it down to lower voltages, but many op-amps are just fine with +/-12V.

Note: Such a supply does not really have the protection and current limiting of an expensive bench supply so you should at least fuse the outputs so that they can't burn up any wires you attach.

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If you want to try a "rail-splitter", chip the TLE2426 is designed for this task, but note that you'll end up with limited ground sink/source capability (read the datasheet carefully), an oddball chip, and your split 'ground' will not be at the same potential as your power supply ground, possibly causing problems if you are using things like USB-to serial cables, oscilloscopes and USB-powered microcontroller in-circuit emulators that are earthed.