Op-amp resister circuit analysis

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SUMMARY

The discussion focuses on analyzing an ideal op-amp circuit to determine the resistor R2 and the current I2 given specific voltage inputs. With Vin set at 500mV, Vout at 2.5V, and R1 at 5kΩ, the calculated value for R2 is 1,250Ω. The current I2 is determined to be 0.4mA using the formula I2 = Vout / Req, where Req is the equivalent resistance of R2 and R1. The discussion emphasizes the importance of understanding the relationship between V+ and V- in ideal op-amps.

PREREQUISITES
  • Understanding of ideal op-amp characteristics
  • Familiarity with Ohm's Law
  • Knowledge of voltage divider equations
  • Basic circuit analysis skills
NEXT STEPS
  • Study the closed-loop non-inverting gain formula for op-amps: Acl = 1 + R1/R2
  • Explore practical applications of op-amps in circuit design
  • Learn about non-ideal op-amp behaviors and their effects on circuit performance
  • Investigate different resistor configurations in feedback circuits
USEFUL FOR

Electrical engineering students, circuit designers, and anyone interested in understanding op-amp circuit analysis and design principles.

joel amos
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Homework Statement


Given the ideal op-amp, determine the resistor R2 and the current I2 where Vin=500mV, Vout = 2.5 V, and R1=5kV.
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Homework Equations


No current passes through op-amps, the op-amp tries to make V+ and V- equal.
Ohm's law, voltage divider equation

The Attempt at a Solution


Since V+ is 500mV, I assumed that the node between R1 and R2 must also be 500mV, as it is connected to V-. So 500mV = 2.5V(R2/(5000Ω+R2)). I got R2 to be 1,250Ω.
Then I found I2=Vout/Req = 2.5V/(1250Ω + 5000Ω) = .4mA.
However, I am unsure because I am not sure if I did the part with the op-amp right; namely, the node between the resistors being set to 500mV.
 
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You are 100% correct sir.

V+ = V- in ideal opamps...

Nice job.
 
Yes - and for the future you can use the general closed-loop non-inverting gain formula (assuming an ideal opamp): Acl=1+R1/R2.
 

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