Bipolar power in the field?

There's a lot of ways of providing split supplies.

If you are asking

1. Can I use 2 12V batteries to provide +/-12V Yes. Use the junction between them as circuit common

1. Do the voltages on the + and - power pins for the opamp have to be identical and opposite?

More difficult. If the supplies are properly bypassed probably yes, but other things (such as common mode range) will be dependent on it.

Give us more information on the intended application if you need a more definitive answer.

Cheers

PeteS

they make Dc-DC converters for that so that you can not only isolate but you can generate dual rail supply from a single rail. Look for DC-DC converters with + & - output

Hi, Ken. You can connect two batteries in series as mentioned by Pete S. Connect the - terminal of battery 1 to the + terminal of battery

1. Then, the + of battery 1 will be +12V, the connection will be 0V or common, and the - terminal of battery 2 will be -12V. That may be the easiest way to do it, and is probably the best way to go for a newbie. It also has the inherent advantage of very low power supply noise and no ripple.

There are a number of "clever" ways to do this, which don't require lugging around two gel cell batteries (kind of heavy, take up quite a bit of space). You can use a DC-to-DC converter, which will convert

Mouser has the Datel BST-12/105-D5 3 watt W DC-DC converter that will do this job, for $28.60 in single quantity.

Or you can use two 555s to build a voltage doubler and a voltage inverter to convert +6V into +/-12V (less a couple of diode drops). But both of these solutions will add power supply noise considerations into your circuit that you might not need.

Most old split supply op amps like the venerable (and practically obsolete) LM741 are specified for "balanced" split supplies, but they'll work perfectly well as long as both supplies are more than 3V higher/lower than the input voltage range. I don't believe this was true for the uA709, LM101 or some of the real fossils, but they're gone, anyway (thank St. Liebowitz!).

I'm wondering, though, whether you might better spend your time looking at other options, if your project isn't "in the can". Single supply op amps have been very common for over twenty five years. Most anything you can do with the old split supply op amps can also be done with single supply ICs with a little craftiness. And that will solve your problem of portable split supplies.

If you care to post again with more information, you might learn how you can run your project on a single supply with three or four AA batteries.

Good luck Chris

Hi, Pete.

It is for the TL084's on this $5 mixer kit:

From the other helpful posts and some additional web searching, it appears that this is a fairly hot topic and the component manufacturers offer various solutions -- none of which have been implemented in a resonably-priced retail package. Designing a circuit from scratch around some of these chips is beyond my abilities.

The kits mentioned in the eBay ad require an AC source; this is not helpful as I won't have A/C in the field. 9-13.8V DC is available.

Ken C

I googled "virtual ground." Here's one link:

Yes, very interesting. Any idea how much curerent I could put through the Sijosae splitter? That looks like a $1 solution. The splitters with active compnents all look like $10+ solutions.

Ken C

for what you're doing the TLE2426 alone has enough to drive your Op-amp.. they are commonly used for some things like that. they are only 20ma how ever, i don't think you'll be using that much any ways and they regulate well.

In addition to the other posts, is it possible to run the circuit in question on +/- 9V? Many op amps circuits are perfectly happy with this, as long as you are not asking them to go too close to the rails. And those little batteries sure are small and convenient!

Best regards,

Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis

On Sun, 04 Feb 2007 04:15:38 -0500, Ken C wrote:

---

Here's an LTSPICE circuit list showing a 555 working as a negative charge pump that ought to work for you:

Version 4 SHEET 1 880 748 WIRE 208 160 -400 160 WIRE 784 160 432 160 WIRE 208 224 144 224 WIRE 624 224 432 224 WIRE 656 224 624 224 WIRE 784 224 784 160 WIRE 784 224 736 224 WIRE -224 288 -320 288 WIRE -176 288 -224 288 WIRE -64 288 -112 288 WIRE -48 288 -64 288 WIRE 48 288 16 288 WIRE 208 288 112 288 WIRE 480 288 432 288 WIRE 512 288 480 288 WIRE 624 288 624 224 WIRE 624 288 592 288 WIRE 208 352 176 352 WIRE -320 368 -320 288 WIRE -224 432 -224 288 WIRE -64 432 -64 288 WIRE 144 448 144 224 WIRE 480 448 480 288 WIRE 480 448 144 448 WIRE 176 480 176 352 WIRE 784 480 784 224 WIRE 784 480 176 480 WIRE 784 496 784 480 WIRE 480 512 480 448 WIRE -400 592 -400 160 WIRE -320 592 -320 448 WIRE -320 592 -400 592 WIRE -224 592 -224 496 WIRE -224 592 -320 592 WIRE -64 592 -64 496 WIRE -64 592 -224 592 WIRE 480 592 480 576 WIRE 480 592 -64 592 WIRE 784 592 784 576 WIRE 784 592 480 592 WIRE -400 640 -400 592 FLAG -400 640 0 SYMBOL Misc\\\\NE555 320 256 R0 SYMATTR InstName U1 SYMBOL voltage 784 480 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL res 608 272 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 24 58 VTop 0 SYMATTR InstName R1 SYMATTR Value 20k SYMBOL res 752 208 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL res -336 352 R0 SYMATTR InstName R3 SYMATTR Value 1000 SYMBOL cap 464 512 R0 SYMATTR InstName C1 SYMATTR Value .01e-6 SYMBOL diode -176 304 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL diode -80 432 R0 SYMATTR InstName D3 SYMATTR Value 1N4148 SYMBOL polcap -240 432 R0 SYMATTR InstName C4 SYMATTR Value 1000e-6 SYMBOL polcap 16 272 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName C2 SYMATTR Value 100e-6 SYMBOL polcap 48 304 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName C3 SYMATTR Value 100e-6 TEXT -376 616 Left 0 !.tran .25 uic

-- JF

Hi John, I see these "circuit lists" posted often, I'm new to LTspice and don't know how to insert such a list into the program. What steps do I take to run the simulation you posted. Thanks, Mike

Thanks, John