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I was buildiing an amplifier circuit for +ve voltages only. When I used a 9V battery to supply V+ and V- (+ to V+, - to V-), I get a constant 8V at the output of the opamp. The output is not changing with respect to input. The circuit worked fine when I used a +/-12V dual power supply. However the way I understand it, using a single supply is okay as long as I'm not dealing with negative input voltages.

sixter
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  • Choose to have both inputs near V+/2 and expect DC to Vout=V+/2 , you may have to AC couple unless you can define here – Tony Stewart EE75 Mar 30 '18 at 03:18
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    What op amp are you using? – C_Elegans Mar 30 '18 at 03:21
  • You mean +/-12V. I tried dividing a 9V battery to make a dual supply, but when I connect it to the opamp, I get different voltages at + and - terminals. – sixter Mar 30 '18 at 03:21
  • @C_Elegans LM741 – sixter Mar 30 '18 at 03:22
  • Can you simply use two 9V batteries to provide +9 and -9 volts to the opamp power pins? – Michael Karas Mar 30 '18 at 04:09
  • Can you show us the schematic for the amplifier that worked with \$\pm\:12\:\text{V}\$? It would go a long way in helping you, I think. There are different approaches to getting something working on a single \$9\:\text{V}\$ supply (with \$1-2\:\Omega\$ series impedance.) – jonk Mar 30 '18 at 04:45
  • You could consider a [discrete rail splitter](https://electronics.stackexchange.com/questions/348485/is-there-a-good-topology-for-splitting-a-dc-power-supply-from-a-few-lm2576-and-l/348506#348506). It's not designed for an 9 V battery. But at least you can see the complexity involved. You really need to specify the current compliance you need. – jonk Mar 30 '18 at 06:10
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    [Reasons not to use a 741](https://electronics.stackexchange.com/questions/304521/reasons-not-to-use-a-741-op-amp/304522#304522) – Andy aka Mar 30 '18 at 07:35

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According to page 4 of the LM741 datasheet, the minimum supply voltage is +/- 10V, so powering it with +/-9V isn't guaranteed to work. The LM741 is a very old design, and its characteristics are not as good as modern op amps (that being said, it works fine, but it's not what I'd pick for a new design). I'd recommend getting a more modern op amp, you probably want one with rail to rail inputs and outputs as well as a lower minimum supply voltage. I've narrowed down the listing here, you still will want to make sure whatever you pick can use the supply you're planning to use.

C_Elegans
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