# The output of Op-Amp[LM324] has error as non-inverting Amp

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1. Apr 25, 2015

### booboo1

Hi everybody
I'm a newbie and working on LM324 to learn Op-Amp. this is my circuit:

http://img4.uplood.fr/free/qx3o_20150425_172843.jpg [Broken]
One of the resistors is 217ohm and another 978ohm. then the gain should be 4.50691 as you can see. so far so good. I know this is for ideal Op-Amp. I applied 0.15v to the input and got 0.94v in the output. then the gain is 6.26667. again I applied 0.35v to the input and got 2.03v then gain should be 5.8!?
again I applied 1.86v and got 10.31 then the gain is 5.54301! holy crap! why isn't the gain stable? because of input offset voltage? How can I stabilize it?

Last edited by a moderator: May 7, 2017
2. Apr 25, 2015

### Averagesupernova

You need a split supply to make this work.

3. Apr 25, 2015

### jim hardy

LM324 should be okay with single supply so long as everything stays positive,.
But if you're inputting AC then yes, you need dual supply.

Did you bypass your supply with a small cap near the IC?

What is voltage at junction of 217 - 978 resistors?
Is it the same as your input?
If opamp is making its inputs equal , the problem is not offset.

Possibly it's your layout. When power supply current shares a wire with signal, the drop along the wire adds to signal.
Is there any AC in your output?
How are your input source and 217 tied to common ?

4. Apr 25, 2015

### Averagesupernova

The gain for a non-inverting op-amp is not how you are computing it. The gain in this case is 5.50691. (978/217) + 1. Keep your input voltages farther away from the supply rail with a 324.

5. Apr 25, 2015

### jim hardy

Thanks - i missed that !
Big ten-duh on me, good buddy !

6. Apr 25, 2015

### booboo1

Thanks guys
I used 145.6kohm as Rf and 2.14kohm as Rin and got an acceptable output. for example 70.1mv in the input, I got 4.93v in the output.

7. Apr 26, 2015

### otpowell

MultiSim is my best friend when troubleshooting circuits like this. Just a suggestion.