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relationship between V-input and Vcc in operational amplifier

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picozero

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Hi
I had some problems using amplifier for gaining something or as passband, and I start thinking is due to relationship between the signal voltage I use and the supply voltage (Vcc).
I need to use an input of about 2 V and I used a Vcc of 9V.
Reading the datasheet of the amplifier I am using an LM358
https://www.electro-tech-online.com/custompdfs/2011/04/LM158.pdf

I noticed this graph in page 6:
**broken link removed**

Idiotic question:

Does it mean that for a certain input Voltage, I should chose a specific Vcc ?

What should it happen if I use less or more Vcc Volts ?
 
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It would basically say that if you wanted a +-5 V swing, you would need at least -5 negative and +7 for the positive voltage of the op amp if I read the 7 right pon the graph. It can be larger. e.g. +-12 as supply.
 
Last edited:
It would basically say that if you wanted a +-5 V swing, you would need at least -5 negative and +7 for the positive voltage of the op amp if I read the 7 right pon the graph. It can be larger. e.g. +-12 as supply.

Ah, ok ,thanks... so it has nothing to do with what I thought:
If I have power supply of +7V (the LM358 is single supply), the input has to be maximum +-5V and the consequent gained signal should not go further +7V.
 
It's generally OK to saturate an OP amp in comparitor applications. In linear applications, it introduces a non-linearity. You should pay attention to the maximum voltage applied to the inputs though.
 
You are asking about the common-mode range of the inputs. For any application where the LM358 is operated as a linear feedback amplifier, the voltage at the non-inverting input is within ~1mV of the inverting input (virtual ground). The LM358 has an input common-mode range from Gnd to Vdd-1.5V, meaning that if the amplifier is powered from 9V, the inputs are allowed to be within the range 0V to 7.5V and it will work as specified. If you tried to use it as a difference amplifier where both inputs were say 8.5V, the results are unpredictable.
 
Graph is showing max output voltage excursion for different supply voltages. Maximum positive output voltage is always abt. 2V smaller than positive supply voltage. As mentioned above for 10Vpp output voltage you must use at least +7V and -5V supply or more.
 
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