Can I get +12v and -12v from a 9v battery?

[alparent]

Can I get +12v and -12v from a 9v battery?

[iccaros]

depends, how much current do you need. you can always voltage boost to 24 volts and set your ground at the half way point.  But depending on why you need this, it may not give you the needed current.

[Seljer]

yep. but you're going to have to use an inductor/transformer

read up on flyback converters

[armdnrdy]

This is probably "alparent" to you but,

Depending on what space constraints you have, the easiest way to get +12v and -12v from a 9v battery is to use two 9 volt batteries, a positive 12 volt regulator, (LM7812) a negative 12 volt regulator, (LM7912) and the usual filter caps.

[PRR]

Why do you "need" +12V?

Many such circuits will be fine with +9V.

Get -9V with a doubler.

It is often simpler to hammer the circuit to fit available power than to cobble-up some complicated power scheme.

[alparent]

I'm building this with my son.
http://www.musicfromouterspace.com/index.php?MAINTAB=SYNTHDIY&PROJARG=WSG2010/wsg_page9.html&VPW=1352&VPH=550

Then this for myself
http://www.musicfromouterspace.com/index.php?MAINTAB=SYNTHDIY&PROJARG=WSG2010/wsg_page9.html&VPW=1352&VPH=550

[merlinb]

I'm building this with my son.
http://www.musicfromouterspace.com/index.php?MAINTAB=SYNTHDIY&PROJARG=WSG2010/wsg_page9.html&VPW=1352&VPH=550

That appears to run off a 9V battery, no?

[alparent]

That one is   Sorry, wrong link.

This is the one I'm building with my son.
http://www.musicfromouterspace.com/index.php?MAINTAB=SYNTHDIY&PROJARG=TENSTEPSEQUENCER/TENSTEPSEQUENCER.php&VPW=1352&VPH=523

[alparent]

This is probably "alparent" to you but,

Depending on what space constraints you have, the easiest way to get +12v and -12v from a 9v battery is to use two 9 volt batteries, a positive 12 volt regulator, (LM7812) a negative 12 volt regulator, (LM7912) and the usual filter caps.

I guest it's not "alparent" to me!
But using 2 9V batt would give me +18v or (+9v & -9v) no?
How do you get to 12v?

[armdnrdy]

Yeah,

I was drinking coffee to wake up after work....I forgot a major component.....the charge pump! 

Should read:

Two batteries in series =18 volts, charge pump, (LT1054CN) positive voltage regulator, (LM7812) negative voltage regulator, (LM7912) and the usual filter caps.

[alparent]

Aren't those charge pump rated at 12-15v? If you are lucky!

So it would be more like:

Two batteries in series =18 volts, 12v positive voltage regulator, (LM7812), charge pump, (LT1054CN) and the usual filter caps.

[iccaros]

if you do two of these http://www.geofex.com/circuits/+9_to_33.htm where you are using this http://www.geofex.com/circuits/+9_to_-9.htm as a reference for negative voltage.  you may still need to regulate to 12 and -12, as these multiply voltage. All of this sounds like a lot of work that if we dumped the batteries you could use a simple AC power supply and regulate to what you want.

the LM2575T is another option, its has plans for a + and - Power Supplies in its datasheets.

And this is probably too big for you? http://www.futurlec.com/Mini_Power_Dual_12V.shtml

In any case it will take some space, cool project though.

[armdnrdy]

Aren't those charge pump rated at 12-15v? If you are lucky!

So it would be more like:

Two batteries in series =18 volts, 12v positive voltage regulator, (LM7812), charge pump, (LT1054CN) and the usual filter caps.

Yes! You are correct sir!
Now it's morning and I'm drinking coffee again and not thinking clearly!  

I've used this design in several builds and it works fine. Remember to add a cap (5-25pf range) across pins 2 (cap+) and 7 (osc) to raise the frequency out of audio (human hearing) range.

[merlinb]

Does it really need to be battery powered? At 30mA consumption you'll be lucky to get 15 hours life out of a PP3.

Anyway, how about a couple of IWD512SA or IWA1212SA DC-DC converters?
http://www.xppower.com/pdfs/SF_IW.pdf

[Hemmel]

12 volt regulator, (LM7812) a negative 12 volt regulator, (LM7912) 

Thanks Larry !!!
I have both at home and I just thought they were different models of the same thing. Now I know the 7912 is for negative 12V !!!!

[alparent]

Does it really need to be battery powered? At 30mA consumption you'll be lucky to get 15 hours life out of a PP3.

Anyway, how about a couple of IWD512SA or IWA1212SA DC-DC converters?
http://www.xppower.com/pdfs/SF_IW.pdf

Isn't there something like that on old network card?

As for battery life......I've noticed the consumption. But I also wanted to be able to use a standard 9v power supply.
Maybe I'm complicating things to much again? 

[PRR]

Sequencer and such, you really want a good power supply. And IMHO, separate from your pedalboard, because they are very different systems.

(And +/-15V, because conventional 1V/Oct systems often do need to be pushed to full nominal 10V output, which is pretty tight under 12V supply.)

Buy a +/-15V supply and get on with it; boosting bumping and flipping 9V is time and aggravation which distracts you from the good stuff.

[R.G.]

As for battery life......I've noticed the consumption. But I also wanted to be able to use a standard 9v power supply.
Maybe I'm complicating things to much again? 

Here's the real way to look at this.

Power out equals power in minus losses.

To figure out if and for how long anything will power anything else, you need to know first how much power is being sent to the powered thing. To do that for an electrical system, you need to know the necessary voltage(s) and current(s).  When you know the necessary power out (summation of the voltage x current products to be delivered) then you can look at what is needed to supply the power in.

You are setting the voltage in by insisting on 9Vdc. You need to know the currents. Let's say you need 50ma from both of +15 and -15. That's 30*0.05 = 1.5W. If you need different currents, you can do the math.

Batteries have a limited amount of energy (Watt-seconds) stored in them. This is usually expressed as the number of ampere-hours they can supply, the voltage being whatever the battery supplies. 9V alkaline batteries can do about 0.4 to 0.5 ampere-hours. So with a **PERFECT** voltage converter, such a 9V battery will supply the 167ma that 1.5W represents at 9V for between two and three hours. It is quite difficult for an amateur to design a power converter that's better than 80%, so in reality this would contract to about two hours, best case. That's with a purely switching converter. With a switching converter plus linear regulators, the efficiency goes down and so does the battery life.

You can sidestep the issue of limited power in the battery by going to a 9Vdc adapter. These are easily available in ratings up to an ampere or more. This relieves the problem of efficiency. Now you're left with the problem of voltage conversion.

You have only two realistic choices for this, a complex charge pump converter setup with multiple pumps, or a magnetic/transformer setup. The charge pump setup will be complicated and require several ICs. The magnetic setup will require special control chips and special magnetic parts. These may or may not be available. It's in general beyond the average level of expertise in this forum to design and wind the magnetics. Some of us could. Most could not do it successfully without many iterations.

I'm with Paul on this one. Get a +/-15V supply, or even two identical adapters, one to make +15V and one to make -15V. Then go enjoy the circuits. Concentrate on the fun stuff, not the PITAs.

Mouser has this: http://www.mouser.com/ds/2/410/SU150-0560-3003.pdf  which makes 15Vdc at up to 0.56A, for $7.36. Two of them will be less than $15.00, and will give you all the 15V you need.  There are many power supplies there that make +/- 15V directly from the same AC power input for under $40.00, but I do not recommend that you mess with wiring AC power.

[Cliff Schecht]

Glad somebody pointed out that these synth type designs really do require a rigid power supply design or things will start to drift all over the place. Even if you implement something fancy like a flyback, you really have to overdesign the "unregulated" negative output so it doesn't droop under heavy loading.

I like linear regulators to drive my synth power supply circuits (even if the linears are powered by a switching supply) because it's simple to obtain good PSU accuracy and regulation on both the positive and negative rails. I designed a switcher for PAiA that output +/-15V which we used to drive +/-12V regulators. Worked really well IMHO.

[armdnrdy]

I designed a switcher for PAiA that output +/-15V which we used to drive +/-12V regulators. Worked really well IMHO.

Would Cliff like to share that design?