# Ideal Op-Amp Question

Discussion in 'Homework Help' started by KillerZ123, Jan 30, 2011.

1. ### KillerZ123 Thread Starter New Member

Nov 25, 2010
7
0
I have an Op-amp that looks like this:

and I am trying to derive this equation for Ix:

$I_{x} = (V_{s})\frac{R_{1}R_{3}}{R_{x}(R_{1}R_{3} - R_{2}R_{4}) + R_{1}R_{3}R_{4}}$

Here is what I have so far:

$V_{-} = (V_{o})\frac{R_{1}}{R{1} + R_{2}}$
$V_{-} = V_{+}$

I1 going through R4 is:

$I_{1} = \frac{V_{s} - (V_{o})\frac{R_{1}}{R{1} + R_{2}}}{R_{4}}$

I2 going through R3 is:

$I_{2} = \frac{(V_{o})\frac{R_{1}}{R{1} + R_{2}} - V_{0}}{R_{3}}$

Then Ix is:

$I_{x} = I_{1} - I_{2}$

I am not sure if this is correct up to here?

2. ### Georacer Moderator

Nov 25, 2009
5,142
1,266
You are OK so far. There is a very good simplification to be done in the I2 current formula.

Add the equation V+=Ix*Rx and you are good to go.

3. ### KillerZ123 Thread Starter New Member

Nov 25, 2010
7
0
OK I got it thanks for the help.

4. ### Georacer Moderator

Nov 25, 2009
5,142
1,266
Glad to hear you solved it.