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If I give 1v as an input to this inverting opamp, the output should be -10v just to make the difference between the input terminals 0. But when I solve the circuit using KCL for 1 volt input I get 1000v as output ?

here is my calculation:

Va= Voltage at inverting terminal Vo = output voltage,

let Va = 0 (due to virtual ground at inverting terminal); (Vin-Va)/Rin = 10mAmps [that flows through input] [this 10 mAmps should also flow in the feedback path since no current goes into opamp], so 10mAmps * Rf = 1000V across feedback resistor

so Vo - Va = 1000volts

since Va = 0 Vo=1000V output when I should have -10v at output for virtual ground (0v at Va)

can someone clarify ?

Also why is that we have a voltage divider between Rin and Rf for voltages other than Virtual ground at say inverting OpAmp terminal?

thanks.

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  • \$\begingroup\$ Can you explain what exactly you want to say with the final question, "Also why is that we have a voltage divider between Rin and Rf for voltages other than Virtual ground at say inverting OpAmp terminal?" You want to understand the role of the voltage divider... or something else? \$\endgroup\$ – Circuit fantasist Jan 23 '15 at 9:16
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1V / 10k = 0.1 mA, not 10 mA. Then Va-Vo = 0.1 mA * 100k gives Vo = -10v.

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  • \$\begingroup\$ what happens if the output is distorted to zero volts by some means? what will the feedback do? \$\endgroup\$ – Mathav Raj Oct 23 '16 at 15:49
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    \$\begingroup\$ Distorted to zero how? \$\endgroup\$ – alex.forencich Oct 23 '16 at 20:06

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