Op-amp resister circuit analysis

  • Engineering
  • Thread starter joel amos
  • Start date
  • #1
104
0

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.
30u4xv5.png

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.
 

Answers and Replies

  • #2
psparky
Gold Member
884
32
You are 100% correct sir.

V+ = V- in ideal opamps...

Nice job.
 
  • #3
LvW
886
239
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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