modified 9 years ago

Another Question about the op amp

01:05:13

So if you openthe switch on the bottom, then 2 2.5Volts become 5V at the end, if you open the top switch then the outcome becomes 2.5-0.5=2V.

But when both switches get closed, it becomes 4.25V instead of 2.5+2.5-0.5=4.5V?

So why does it do that?

published 9 years ago

hurz

9 years ago

http://everycircuit.com/circuit/5498279259537408

lmccoig

9 years ago

Op- amp is powered by 15 volts. Are you considering input power from op-amp?

hurz

9 years ago

Opamp power here is irrelevant

mcdonalds

9 years ago

When performing an analysis on an op amp in this form you would do analysis by superposition on both sides. Analysis on the inverting side is as normal. On the non inverting side you would find the gain of the circuit by connecting the inverting side to ground an analyzing. It would end up being: (R4/R4+R5)(1+RF/R1||R2) which equals 0.75 in this case. Then it's back to a differential op amp which makes it 5V-0.75V = 4.25V

mcdonalds

9 years ago

Rf is your feedback resistor, R1&2 are your inverting side resistors and R4&5 are non-inverting side

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