Electronic – Is it normal that with the same op amp but with a different voltage input, the amplifier gain is different

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So with my one of the part of my circuit below, I only wanted to see the effect on the op amp if I changed the input voltage (knowing that the inverting input is 0). My first thought was that even if I changed the input voltage, the output would changed accordingly so that the amplifier gain stays the same (since it's the same op amp).

So I first set my input voltage as 7V and found the output voltage was 8.5V.
Then I changed my input to 14V (double of the initial input) and found out that the output voltage was still 8.5 Volts. Now I am totally lost since my initial hypothesis is wrong.

Can someone guide me on where I was wrong?

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Best Answer

Your output is not changing because it is saturated at the upper rail of the op-amp, which is somewhat below 9V. You will find that any voltage you give this thing above zero will show the same result. That is because it is acting as a comparator: the output will be "high" as long as the positive input exceeds the negative input. If you want different behaviour, you have to connect feedback circuitry to modify the gain, because currently the gain is ideally infinite. I do not know what simulation software you are using nor its model for an op-amp, so it's a bit of guesswork what the gain is actually limited to, but for your purposes it's infinite.