I'm working on a pre-amplifier using the INA217, but I couldn't get a linear operation for Vout. I saw that I can use this op-amp as single supply, but I can't make that work. Any suggestion?
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First, when I made the following circuit, I did not get the gain from the datasheet, which was G=1 + (10k/RG).
I used a symmetric source made from a two channel voltage supply to provide the +5 and -5 V, and Ref and Vin- connected to the virtual ground, as shown in the figure.
Is that right or a I made something wrong? If it's right, why didn't I get the gain equal to 2?
Second, for the Single Supply Voltage, I used the following circuit.
Again, I used RG=10k ohms to make the gain be 2. And I used Vcc=5 V, the values from Vin wil be varying between 0 and 2 V, so I think I'm not going to have problem with saturation.
Thanks in advance,
Thank you for the quick and elaborate reply
The 4th sentence of the data sheet reads the device works from +/- 4.5 to +/- 18V
Hence for the device to used in single supply the V+ should be atleast equal to 9V
Thus the single supply case shown above is not possible as you have mentioned with INA217 as V+ is only 5V
The input common mode range for the INA you have used is given below
positive rail direction = (V+) - 4V
negative rail direction = (V-) + 4V
The output limitation is given below
(V+) - 2 V
(V-) +2 V
for a +/-5 V supply as you have mentioned in case 1 ,
for the output to be linear with respect to your input , the output needs to be between -3V to +3V only
And your input needs to be -1V to +1V only
As you are supplying a signal of 0 to 2 V with a gain of 2 ,
your are violating both the conditions (input and output)
Hence you are not able to get a linear relation between input and output which is making it appear like your gain is not equal to 2
for a +5 V and GND supply as you have mentioned in case 2 ,
for the output to be linear with respect to your input , the output needs to be between +2 to +3V only
and the input common mode range is violated in all cases
Hence device cannot be used with a +5V single supply as mentioned earlier
hence i would recommend using a INA in which the common mode voltage range is not violated and output is also within the specified range
Also you can tweak your inputs as shown below to make sure you are not violating the input common mode range
I'm sorry but I didn't get the values that you mentioned for the input and output range in all cases.
In my understanding, in case 1, if I use +-5 V supply, I expect a maximum output voltage range of +-5 V, but you said that it needs to be between -3 to 3 V. Could you please show me how you found those values? And also, I don't understand the limitation on the input values.
Sorry, I'm a beginner :)
In electronics all of us are beginners , always
No need to feel bad about it :)
I would recommend you to watch a 10 min video at this point of time
Please click on the link above and go through the video on input and output limitations explained wonderfully by my colleague
I believe the video will help you understand clearly the common mode limitation issue
I watched the video and I fully understand what was going on with my circuit! Thank you so much for you help (and the video that is super detailed!)
However, I took a look at another component's datasheet - http://www.ti.com/lit/ds/symlink/opa2137.pdf - and I don't have a max value for Common-mode voltage range.. I have only (V+)... does that mean any default range or something like that?
Thank you again!!!! Sorry for being detouring the post.
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