Bipolar power in the field?

[Ken C]

Is there a clever way to create a +-12V bipolar supply for the field?

It will be powering op amps on a PCB.

Could I use two 12V batteries in series? Or does the positive side
voltage have to the exact same manitude as the negative side voltage?

Ken C

 

[PeteS]

Is there a clever way to create a +-12V bipolar supply for the field?

It will be powering op amps on a PCB.

Could I use two 12V batteries in series? Or does the positive side
voltage have to the exact same manitude as the negative side voltage?

Ken C

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

2. 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

 

[Jamie]

Is there a clever way to create a +-12V bipolar supply for the field?

It will be powering op amps on a PCB.

Could I use two 12V batteries in series? Or does the positive side
voltage have to the exact same manitude as the negative side voltage?

Ken C

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

 

[Chris]

Is there a clever way to create a +-12V bipolar supply for the field?

It will be powering op amps on a PCB.

Could I use two 12V batteries in series? Or does the positive side
voltage have to the exact same manitude as the negative side voltage?

Ken C

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
2. 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
4.5V or 6V (three or 4 AA or C batteries) into the +/-12V you need.

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.

http://www.mouser.com/index.cfm?handler=home

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

 

[John Fields]

Is there a clever way to create a +-12V bipolar supply for the field?

---
Several.
---

It will be powering op amps on a PCB.

Could I use two 12V batteries in series?

---
No.

You just have to make sure that the outputs of the opamps will never
try to go higher than the positive supply voltage minus their
specified headroom to the positive rail or lower than the negative
supply voltage plus their 'footroom' specified to the negative rail.

 

[Ken C]

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

Hi, Pete.

It is for the TL084's on this $5 mixer kit:
http://cgi.ebay.com/ws/eBayISAPI.dl...K:MEWA:IT&viewitem=&item=6031715442&rd=1&rd=1

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

 

[kell]

Is there a clever way to create a +-12V bipolar supply for the field?

It will be powering op amps on a PCB.

Could I use two 12V batteries in series? Or does the positive side
voltage have to the exact same manitude as the negative side voltage?

Ken C

I googled "virtual ground." Here's one link:
http://tangentsoft.net/elec/vgrounds.html
Even if you don't use a virtual ground, it's interesting.

 

[Ken C]

I googled "virtual ground." Here's one link:
http://tangentsoft.net/elec/vgrounds.html

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

 

[Jamie]

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.

 

[Bob Masta]

Is there a clever way to create a +-12V bipolar supply for the field?

It will be powering op amps on a PCB.

Could I use two 12V batteries in series? Or does the positive side
voltage have to the exact same manitude as the negative side voltage?

Ken C

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
www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
Science with your sound card!

 

[John Fields]

Hi, Pete.

It is for the TL084's on this $5 mixer kit:
http://cgi.ebay.com/ws/eBayISAPI.dl...K:MEWA:IT&viewitem=&item=6031715442&rd=1&rd=1

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.

---

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

 

[amdx]

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

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

 

[John Fields]

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

---
Use something like Notepad to copy the list into to a convenient
directory, renaming it anything-you-like.asc, and then navigate to
it with LTSPICE and click on the file.

When the schematic comes up, right click anywhere there's no
component and then click on 'Run'

 

[amdx]

---
Use something like Notepad to copy the list into to a convenient
directory, renaming it anything-you-like.asc, and then navigate to
it with LTSPICE and click on the file.

When the schematic comes up, right click anywhere there's no
component and then click on 'Run'

Thanks, John