hi 442,
Your calculations in post #19 look OK to me.
E

 

Arthur - as I have mentioned in my post, all these solutions are not correct.
You are not allowed to use the condition (Va=Vb and V2=V3)

So what is the correct method to solve this? Because in post #8 Jony writes that I have to do this.

 

However, if the two opamps both have identical gain, and that gain is less than about 7.051, the circuit will be DC stable.

How did you determine that?

assume the + and - inputs of the rightmost opamp are reversed and then calculate I2 and V3. This calculation will give you a valid result.

Are you sure?

 

hi 442,
Your calculations in post #19 look OK to me.
E

Eric, sorry to say - however, how can this solution be correct?

Look here:
Va=-2V (pos. input opamp).
Gain G=+3
V01= + 6V .

Question: How can the output be positive when the input is negative and the gain positive?
A typical result for an amplifier that is useless because it has no DC bias point in the linear range.

 

So what is the correct method to solve this? Because in post #8 Jony writes that I have to do this.

Arthur, there is no solution which makes sense!! Do you know what it means to say that an amplifier is unstable due to positive DC feedback? It is in saturation!
Recommedation: Ask Jony for a comment.

 

Hi 442,
Give me a few minutes to create a LTSpice simulation, so that we can check your results.

E

 

Arthur, there is no solution which makes sense!! Do you know what it means to say that an amplifier is unstable due to positive DC feedback? It is in saturation!
Recommedation: Ask Jony for a comment.

Arthur, there is no solution which makes sense!! Do you know what it means to say that an amplifier is unstable due to positive DC feedback? It is in saturation!
Recommedation: Ask Jony for a comment.

Ok, I did some quick research on saturation. What I understand from it (and correct me if I'm wrong) is because the op amp has a minimum range of 0V because it is connected to ground. As a result, it cannot reach the -6V on V01.
Is this good ?

 

Ok thanks for helping guys! I understand a little more about it now.

 

hi arthur,
Can we now say the query has been solved.?
E

 

hi arthur,
Can we now say the query has been solved.?
E

Yes

 

Ok thanks for helping guys! I understand a little more about it now.

Can i ask if you know whether or not it oscillates now.