Get negative voltage from a battery

Thread Starter

Dritech

Joined Sep 21, 2011
869
Hi all,
Lets assume a 9V battery is used. I know methods that can be used to get -4.5V, ground and 4.5V, but is there a way to get -9V, ground and 9V?
 

Thread Starter

Dritech

Joined Sep 21, 2011
869
Thanks for the replies.
This will be a portable device so using two batteries will not be best option for my project.
I will be requiring the negative voltage for an operational amplifier supply. Will be MAX232 be good for this application?
 

AnalogKid

Joined Aug 1, 2013
8,487
Depends on the 19 things you are not telling us about the project, like the part numbers, the current requirements, the run time, etc. Charge pump ic's can act as a power inverter, making a negative voltage approximately equal to the positive voltage running the chip, but the output can't make very much current. A switching power control chip in a flyback topology can make a regulated negative output voltage at much higher currents, but makes more conducted and radiated noise that could corrupt your signals.

This is an electrical engineering forum. If you provide some electrical engineering information in your question, you'll get some electrical engineering answers.

ak
 

Papabravo

Joined Feb 24, 2006
13,910
Thanks for the replies.
This will be a portable device so using two batteries will not be best option for my project.
I will be requiring the negative voltage for an operational amplifier supply. Will be MAX232 be good for this application?
Only if you need an RS-232 connection. I mention the chip because it was among the first to generate the ± power supply voltages required by RS-232 interfaces from a +5VDC source. IIRC the original chp produce ±9VDC at a couple of tens of milliamps.
 

ErnieM

Joined Apr 24, 2011
8,045
Why do you need negative supplies when all you want to run are some op amps?

Just use op amps that work off a single supply.
 

WBahn

Joined Mar 31, 2012
25,902
Actually I will be powering 5 op-amps which consumes around 2mA each.
For the supply I will most probably be using a 7.4V LiPo battery.
Can't you use single-supply opamps?

The place to start is with your project requirements. If your project requirements demand max-min voltage rails that exceed the battery you will use, then that is one thing. If your project requirements don't demand this, then don't make things harder than they need to be.
 

Thread Starter

Dritech

Joined Sep 21, 2011
869
Hi again,
My input signals will vary from -50mV to 50mV. If I buy an op-amp with a reference pin for offsetting, I will still need negative supply, no?
 

WBahn

Joined Mar 31, 2012
25,902
What "ground"? Ground (more properly called "common") is just a node that YOU choose to call 0 V. There is NOTHING that says that either terminal of your battery has to connect to this "ground".
 

WBahn

Joined Mar 31, 2012
25,902
Opamp needs positive as well as negative supply.
eg. 8 pin DIP 741 IC
Many opamps are specifically designed to run from a single supply.

Even the ones that aren't can be run from a single supply as long as the signals are biased properly. There is nothing magical about a "negative supply". The opamp has no way of knowing whether either of its supply voltages are "positive" or "negative" relative to "ground", just whether they are positive or negative relative to the signals at the rest of the opamp's pins.

If you have a single 30 V supply and power a 741 opamp from it the amp will be perfectly happy. But your signals should be biased to about the midway point of the supply, or about 15 V, for good results. No need to create a "negative" supply at all.
 
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