Help me wrap my head around rail splitting/virtual grounds

Take a look at these

Lots of others exist as well.

jremington:
Yes, shop around and no (can use 7805 and 7905 regulators or buck converters).

So I am coming up completely dry on dual power supplies... I'm guessing it's because I'm looking for external power supplies. I'd like to avoid internal supplies due to the additional space it will take up and the extra heat it will produce, not to mention the peace of mind from not having mains voltage inside the box at any point. But if I want a power supply that gives bipolar power, it looks like I'm SOL for that.

A few more google searches led me to this: Dual 5V Power Supply Mini Board

This seems like it could be a decent solution, no? I could use a 12 or 15V wall wart, linear regulators for the parts that want 9V, and this board to supply +/-5V to my filter chips. They also make a 12V version if the switching regulators on the 5V version prove to be too noisy. Any reason this wouldn't work? Or am I maybe misreading the page and this simply provides another virtual ground situation, leaving me back where I started?

jremington:
What you are doing does not strike me as designing, but rather, simply hacking something together.

Seems like tomayto/tomato to me. Yes, I'm absolutely hacking stuff together. But at the end, I hope the end up with relatively polished and complete musical instrument that would be at home in a studio, and having two power supplies is at odds with that end goal.

I know it's not as glamorous as designing circuits from the ground up for eventual commercial release, but it's what I find interesting.

relatively polished and complete musical instrument that would be at home in a studio

Good luck doing so without the data sheets for the filter chips.

jremington:
Good luck doing so without the data sheets for the filter chips.

I'm not really too worried about that. Other folks have used these chips in new designs just fine without the datasheet, and they're really pretty simple chips to begin with. Is there anything specific you think I should be careful about?

CrossRoads:
Take a look at these
http://www.trcelectronics.com/IPD/integrated_power_designs_power_supply_srp40.shtml
Lots of others exist as well.

I was hoping to have an external power supply, but it's increasingly looking like that's not an option. Still, the prices on those are well past what I was hoping to spend. I'll keep looking for other options, surely there's something out there.

Did you happen to see the link I posted to the Futurlec board? Does it seem like that might be a simple solution?

Jayteefos:
So I am coming up completely dry on dual power supplies... I'm guessing it's because I'm looking for external power supplies. I'd like to avoid internal supplies due to the additional space it will take up and the extra heat it will produce,

Not easy especially if you need low noise rails for sensitive circuits.
I have a regulated 18 0 -18 wall wart which i had to build myself.

Then i use an on board 15 0 -15 linear reg with additional filtering .

Keeps the mains off the board and the heat down.

Generally i find it far easier to use batteries.

What current do you need and what noise can you tolerate on the rails ?
Switchmode give of little heat but can need careful shielding and filtering.

Boardburner2:
Not easy especially if you need low noise rails for sensitive circuits.
I have a regulated 18 0 -18 wall wart which i had to build myself.

Then i use an on board 15 0 -15 linear reg with additional filtering .

Keeps the mains off the board and the heat down.

Generally i find it far easier to use batteries.

What current do you need and what noise can you tolerate on the rails ?
Switchmode give of little heat but can need careful shielding and filtering.

Yeah, I am a little worried about noise issues with a switching supply. There are parts of this project where clean power isn't necessary, but since this is directly powering an analog filter, it's probably best to stabilize it as much as possible.

I am unsure of current draw right now, but I expect it to be modest. Tens of mA, somewhere in that range.

Since it's only the one bit that needs the bipolar power supply, right now I'm looking into DC-to-DC 7805/7905-based supply circuits. Should give me better noise specs than the Futurlec supply I linked to above, and should be simple enough to work up on stripboard, which will be nice. That way I can stick with a regular +12-15V wall wart.

Thanks for your help. Seems like every time I clear a roadblock on this project (this has been a pipe dream/pet project of mine for almost 10 years, and I'm only just now getting knowledgeable enough to pull it off right) a new one pops up! Still, getting much closer! Onward!

Have a look at the Murata NMA series of DC-DC converters. I've used the NMA0505SC in audio circuits (Volume control circuit) with very good results. It does depend on how much current you require though, but they do similar modules with higher wattage.

Ian.

ian332isport:
Have a look at the Murata NMA series of DC-DC converters. I've used the NMA0505SC in audio circuits (Volume control circuit) with very good results. It does depend on how much current you require though, but they do similar modules with higher wattage.

Ian.

Hey! Nice find, I think that'll be the one. Put 12V in, get +/-5V out. Perfect. I really can't imagine needing more than 100mA.

Thanks a ton! :slight_smile:

Jayteefos:
That way I can stick with a regular +12-15V wall wart.

Good idea to keep mains off the board.
Hum can be a problem sometimes.

This article is a fairly good explanation of dual psu.

I use fig 5 or similar normally.

Tracking regulator can be important for dual rail op amp use , not just two separate supplies.

Depends on the circuit.
Also not that power up can be important , the rails should power up at the same rate.

To get to one external power supply, just buy the components and 'throw' them in an enclosure. One cable in, one cable out.

Use an AC wall wort. Rectify it and filter
it in your enclosure.
It is easy enough to create a +/- output with
a half wave rectifier and lots of capacitance.
Regulate is down with linears and add more filters.
Dwight

Hello there,

Just a quick note on power supply splitters.

The things to watch out for are the startup and shutdown behavior of the circuit that splits the supply and provides the central 'ground' reference (usually called 0v).
For example if we had a 10v supply split into +5 and -5 volts, when the 10v supply first turns on it may jump up to 10v right way while the splitter is still ramping up to it's normal voltage which would be 5v in this case which would then be called the ground reference. While it is ramping up anything connected to +5 and the ground reference (0v) will have almost 10v across it for a short time. How well that element handles this higher voltage will depend on what it is. Many things designed for +5v operation do not handle +10v very well, and usually fail even if powered that way for a very brief period. That means the device can blow out during startup. During shut down the same thing might happen.

So for these reasons the circuit has to be tested very carefully if something has to run at the lower voltage but could be subjected to the full supply voltage for some time.

With that in mind, there are many ways to split a power supply. One of the simplest is to use an op amp with the OUTPUT grounded. Obviously the op amp output current capability has to match the application current requirement, and startup and shutdown operation periods have to be tested very carefully.

International Power and Power One still around?
They have several supplies with 5V and +/-12V (or 15).

He's got a plate of spaghetti on the output terminals, but...

MrAl:
Hello there,

Just a quick note on power supply splitters.

The things to watch out for are the startup and shutdown behavior of the circuit that splits the supply and provides the central 'ground' reference (usually called 0v).
For example if we had a 10v supply split into +5 and -5 volts, when the 10v supply first turns on it may jump up to 10v right way while the splitter is still ramping up to it's normal voltage which would be 5v in this case which would then be called the ground reference. While it is ramping up anything connected to +5 and the ground reference (0v) will have almost 10v across it for a short time. How well that element handles this higher voltage will depend on what it is. Many things designed for +5v operation do not handle +10v very well, and usually fail even if powered that way for a very brief period. That means the device can blow out during startup. During shut down the same thing might happen.

So for these reasons the circuit has to be tested very carefully if something has to run at the lower voltage but could be subjected to the full supply voltage for some time.

With that in mind, there are many ways to split a power supply. One of the simplest is to use an op amp with the OUTPUT grounded. Obviously the op amp output current capability has to match the application current requirement, and startup and shutdown operation periods have to be tested very carefully.

Would this issue of voltage spikes still be a problem with the Murata DC-DC converter linked above?

Jayteefos:
Since I'm using a virtual ground for the filter chips, I think this means that the arduino LOW will be at -5V, and the HIGH will be at 0V from the perspective of the filter chips, and that the arduino will never be able to generate a +5V signal that the chips will see as 5V. Does that make sense?

Yep...... it definitely makes sense. That's why the normal route should be taken, such as a mains supply powering a two polarity power supply (eg. +5V, 0V, -5V). If compact form is required, then it'll just be a matter of looking for compact enough form - but also needs to be safe as well. Sometimes....it might not be possible to get particular kinds of devices with particular requirements 'small enough' with present-day technology. Relatively small.... yep....but relatively 'super small' - maybe not.

I assume you're looking for regulated. Those murata ones aren't regulated (I think).

I think it all depends on the actual circuit. Draw it out
and we could analyze it.
You just stating you are going to use some module but
you not shown either how or what loads you expect them
to support.
Dwight

Jayteefos:
Would this issue of voltage spikes still be a problem with the Murata DC-DC converter linked above?

Hi,

Well normally a regulated power supply keeps the voltage between two points (such as ground and Vcc) at a constant level, and during startup the voltage will normally (although not always) be LESS than the specified value. So if you have a 5v output it is not likely that it will go over 5v unless it is forced by some other power supply level like 10v. That could happen if the 10v supply can pump current into the 5v line because many power supplies do not protect against voltages that are applied to it's own output that are higher than the regulation point. So you'd have to check for that condition, based on your actual circuit.
In most cases there's no problem because during startup the voltage will be less than 5v, but there are things to look out for. I'll mention one here to give you an idea how this works, but remember testing is always the best bet.

In the case where we have a 5v p/s output and a 10v output and we have a resistor of 100 ohms between the 10v supply and the 5v supply, if the 5v supply was only loaded by say a 100k resistor (as an extreme example) it is possible that the 5v supply voltage will go up to 10v because there is not enough sink current to keep it at 5v. That's with the typical linear regulator which can only source current and not sink any itself. In this case the min resistor on the 5v supply (the load) would have to be 100 ohms, so that the entire current from the 10v supply would flow through that second 100 ohm resistor.
Of course we dont just connect resistors so it gets a little more complicated. We usually connect devices that need power from both the 5v line and the 10v line. If there are no such devices, then there should never be a problem.

I should say though that most of the time this stuff works fine, and that we just check to see that there may be a problem that's all. Many power supplies have a plus and minus output too, which makes it easier to use.