0
\$\begingroup\$

Schematic

The first op amp's output is 18 V and second's output is 27 V but when I sum those two outputs with a summing op amp, it gives -8.53 V at output. What is the wrong with my circuit? Am I not supposed to read "45 V" at output?

R1 = 1k, R2 = 1k, (non-inverting amplifier)

R3 = 2k, R4 = 1k, (non-inverting amplifier)

R5 = 1k, R6 = 1k, R7=1K (adder)

\$\endgroup\$
3
  • \$\begingroup\$ You are certainly not supposed to see a voltage outside the op-amp supply rails! \$\endgroup\$ Nov 2 '13 at 12:26
  • \$\begingroup\$ Is the simulation model behind those op-amps an ideal op-amp model or a real circuit model of a '741? \$\endgroup\$
    – The Photon
    Nov 2 '13 at 15:35
  • \$\begingroup\$ It's ideal I think..The simulation software is ISIS. \$\endgroup\$
    – whocares
    Nov 2 '13 at 15:40
2
\$\begingroup\$

The adder circuit does add but it inverts the summation about the voltage applied to it's non-inverting input. So an input of A and an input of B becomes C - (A plus B), where C is the voltage on the non-inverting input.

Another problem is that none of the opamps have power rails connected.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.