Hi, do you know why the U2 in this circuit does not buffer the 2,9 Volts at +5Volts on the supply (see attached)?
Thanks a lot for your help.
Sebastien
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Hi, do you know why the U2 in this circuit does not buffer the 2,9 Volts at +5Volts on the supply (see attached)?
Thanks a lot for your help.
Sebastien
It works well when VCC=6,5 volts and above.
Hello Sebastien,
The OPA145 maximum Common-mode voltage (VCM) is rated at (V+) – 3.5 V. Therefore, the maximum positive VCM for a +5 V supply is +1.5 V. In the circuit schematic the VCM is +2.9 V, which exceeds the VCM limit by +1.4 V. The +6.5 V supply sets the +2.9 V input right below a now higher +3 V VCM maximum.
A different op amp having a higher positive VCM limit closer to the supply rail rating would be needed for a +5 V supply application.
Regards, Thomas
Precision Amplifiers Applications Engineering