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limitation of opamp in the single supply differential mode
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VanitarNordic:
Hi,

I have a sensor which is connected to +12V and it shows some small variations at the output.

I have an opamp which I have configured in AC input, inverting amplifier. therefore I should supply it with the load voltage and then find the best value for + rail (by default the half of the VCC which is 6), something like the figure below, but the opamp maximum supply is 3.3V. I am bounded to use this opamp and I can not change the sensor voltage.



is there any method to fix this problem?
Zero999:
I don't fully understand the question.

Are you asking who to use an op-amp powered from 3.3V to amplify the signal from a sensor powered by 12V?

If do, the answer is yes. You might need to add some protection diodes to the op-amp input, if they're not already built-in, to prevent spikes when the AC coupling capacitor charges, on power on.
VanitarNordic:

--- Quote from: Zero999 on April 11, 2019, 09:12:39 am ---I don't fully understand the question.

Are you asking who to use an op-amp powered from 3.3V to amplify the signal from a sensor powered by 12V?

If do, the answer is yes. You might need to add some protection diodes to the op-amp input, if they're not already built-in, to prevent spikes when the AC coupling capacitor charges, on power on.


--- End quote ---

No, the question is when the input is +12 referenced, the suitable voltage for the + rail could be something of course above +3.3V. in this circuit I don't see a correct output except I use a +12V opamp and adjust the + rail to see the desired wave at the output

I have already used the diode and input is AC coupled
Zero999:

--- Quote from: VanitarNordic on April 11, 2019, 09:33:02 am ---
--- Quote from: Zero999 on April 11, 2019, 09:12:39 am ---I don't fully understand the question.

Are you asking who to use an op-amp powered from 3.3V to amplify the signal from a sensor powered by 12V?

If do, the answer is yes. You might need to add some protection diodes to the op-amp input, if they're not already built-in, to prevent spikes when the AC coupling capacitor charges, on power on.


--- End quote ---

No, the question is when the input is +12 referenced, the suitable voltage for the + rail could be something of course above +3.3V. in this circuit I don't see a correct output except I use a +12V opamp and adjust the + rail to see the desired wave at the output

I have already used the diode and input is AC coupled

--- End quote ---
If the AC coupling capacitor has the correct polarity and isn't faulty, once the steady state condition has been reached, the DC voltage on the input should make no difference, to the output voltage of the op-amp. Please post a complete schematic showing the sensor, the op-amp and supply voltages clearly marked.
StillTrying:
It's not very differential, we've been here before. :)
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