Integrator triangular wave

thiagofdp

Joined Nov 6, 2014
4
Guys, I need help with this project.

I have this circuit

This is the project

Here's what I want from V1

Can someone give me a hand? Thanks in advance

MikeML

Joined Oct 2, 2009
5,444
What frequency, rise time, fall time, are you trying to achieve?

R3*C1 determines the rise time. R4*C1 determines the fall time. The sum of these determines period = 1/frequency.

10*R2/R1 determines amplitude.

I question why the inverting input of the second opamp is connect to +5V instead of ground?

Last edited:

thiagofdp

Joined Nov 6, 2014
4
What frequency, rise time, fall time, are you trying to achieve?
it's on the third picture..
rise time 500ms
fall time 1000ms

thanks

MikeML

Joined Oct 2, 2009
5,444

thiagofdp

Joined Nov 6, 2014
4
I question why the inverting input of the second opamp is connect to +5V instead of ground?

MikeML

Joined Oct 2, 2009
5,444
Looks like your math is good. Note that the sim and your analysis depends on the opamps being rail-to-rail output. Note V(b); see how close it must pull to the rails... Note I used repeated trials to get close to your 1500ms period.

thiagofdp

Joined Nov 6, 2014
4
Thanks a bunch!
But it would be a nice a capacitor of lower value, because the period is too damn big
I tried 500k, 1M and 10nF, doesn't work that well... Can you show me how you calculated R3, R4 and C1?
Thans a lot.

MikeML

Joined Oct 2, 2009
5,444
The times are a little difficult to calculate because of the 5V bias on the Schmitt stage. I just played around with R and C until the rise time ~ 1s and fall time ~0.5s. The time constant is roughly R*C = 1e6*1e-6 or 1meg and 1uF gives one second. The input bias current of the opamps puts an upper bound on R. I wouldn't go much over ~1meg. So you are stuck with C.