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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.

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  • \$\begingroup\$ 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 \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 30 '18 at 3:18
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    \$\begingroup\$ What op amp are you using? \$\endgroup\$ – C_Elegans Mar 30 '18 at 3:21
  • \$\begingroup\$ 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. \$\endgroup\$ – sixter Mar 30 '18 at 3:21
  • \$\begingroup\$ @C_Elegans LM741 \$\endgroup\$ – sixter Mar 30 '18 at 3:22
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    \$\begingroup\$ Reasons not to use a 741 \$\endgroup\$ – Andy aka Mar 30 '18 at 7:35
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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.

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  • \$\begingroup\$ I see. Thanks for the answer. I do happen to have an NE5534 op amp with me. Can I use it to overcome these problems? \$\endgroup\$ – sixter Mar 30 '18 at 3:46
  • \$\begingroup\$ Read the datasheet. It will tell you the minimum and maximum supply voltage \$\endgroup\$ – C_Elegans Mar 30 '18 at 3:57
  • \$\begingroup\$ @C_Elegans - Also note that he's not using two batteries - just one. So no +/- 9. \$\endgroup\$ – WhatRoughBeast Mar 30 '18 at 8:27
  • \$\begingroup\$ @WhatRoughBeast two 9v batteries will give you +/-9v. \$\endgroup\$ – C_Elegans Mar 30 '18 at 14:06

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