Based in the accepted answer, with a RC circuit i would obtain a time average of the input voltage, normalized by the reciprocal time constant 1/RC. If i were to implement this circuit what should i expect from this equation:



So lets say i have the circuit below and its input and output waves.



Solving the equation for time equal to 50ms


I get 10... I should have something around 1V. What am i doing wrong

 

Try removing U2 and drive the RC directly from V2.

 

Based in the accepted answer, with a RC circuit i would obtain a time average of the input voltage, normalized by the reciprocal time constant 1/RC. If i were to implement this circuit what should i expect from this equation:

View attachment 280222

So lets say i have the circuit below and its input and output waves.



Solving the equation for time equal to 50ms

View attachment 280237
I get 10... I should have something around 1V. What am i doing wrong

Let's give your basic premise some consideration.

You are claiming that this circuit is going to give the average. But does that make sense?

Let's say that the input voltage is 2 V for 1 s and then 0 V for 1 s. The average would be 1 V. The RC might scale that to some other value, but we can take that into account by considering another example in which the input voltage is 2 V for 9 s and 0 V for 1 s, making the average 1.8 V. Whatever factor the RC imposes get applied to both, so the actual voltage from the second case should be 1.8x whatever the actual voltage from the first us.

Yet, in both cases, that final 1 s with a 0 V input is more than enough to sufficiently discharge the capacitor from whatever value it had obtained. In fact, with a time constant of barely 5 ms, everything that happened more than about 25 ms ago is completely lost. So the circuit does NOT give the average of the input voltage, it favors the recent values of the input voltage with the influence of older voltages decreasing exponentially as since they appeared increases.

How much math have you had? In particular, what techniques do you know to solve differential equations? Do you know Laplace transforms?

 

Let's give your basic premise some consideration.

You are claiming that this circuit is going to give the average. But does that make sense?

Let's say that the input voltage is 2 V for 1 s and then 0 V for 1 s. The average would be 1 V. The RC might scale that to some other value, but we can take that into account by considering another example in which the input voltage is 2 V for 9 s and 0 V for 1 s, making the average 1.8 V. Whatever factor the RC imposes get applied to both, so the actual voltage from the second case should be 1.8x whatever the actual voltage from the first us.

Yet, in both cases, that final 1 s with a 0 V input is more than enough to sufficiently discharge the capacitor from whatever value it had obtained. In fact, with a time constant of barely 5 ms, everything that happened more than about 25 ms ago is completely lost. So the circuit does NOT give the average of the input voltage, it favors the recent values of the input voltage with the influence of older voltages decreasing exponentially as since they appeared increases.

How much math have you had? In particular, what techniques do you know to solve differential equations? Do you know Laplace transforms?

Yes, i know laplace transform

 

Yes, i know laplace transform

So set up the differential equation for your system and solve it using Laplace transforms. You'll see that the solution is NOT just the integral of the input -- there is an exponential decay as well.