741 opamp as a summing amplifier

[cgsgunasekara]

when i implemented a summing circuit with 741 opamp it gives an output of -14.11 V , for V1=12 v dc     v2= 5 v dc    ,    R1=10k and R2=47k     Rf=10k , 

inputs are attached to the inverting input. tBut the theoretical output is

Vo= -(V1/R1 + V2/R2)* Rf = -13.06 v 

what are the reasons for the difference in calculated and simulated outputs?

[GGoodwin]

Hi cgsgunasekara,

There are several possible sources of errors, some are due to imperfections of 741 (or any other op amp), some are due to digital computer arithmetic, some are inherent to the way circuits are simulated. The errors cannot be completely eliminated but these can be reduced or minimized.

Did you connect the noninverting input directly to ground? Try inserting a 4.7 kΩ resistor instead and run the simulation.

Make an observation if the resistances are scaled down by a factor of 2: 5 kΩ, 23.5 kΩ, 5 kΩ, 2.35 kΩ. Then try a factor of 5: 2 kΩ, 9.4 kΩ, 2 kΩ, 940 Ω.

Best regards,

G. Goodwin