Waveform Generator Problem

Russmax

Joined Sep 3, 2015
82
Callum2510,
Never mind the virtual ground thing. Semantics. Terminology is important, but it's no substitute for a correct answer.
Yes, this circuit is non-linear so V+ is not equal V-, most of the time.

Your primary mistake was trying to solve a non-linear, time-domain problem using s-domain analysis.
1st, look at the circuit when it's first turned on. C1 starts at 0 volts. C1 has to charge until V- = V+. So you have to figure out what V+ is at time zero, and what the equation is for C1 charging through R3.
2nd, you have to understand what the op-amp output does after V- = V+. (Now C1 has to (dis)charge to until V- = the new V+) C1 will discharge through R3. Figure out the equation for that.
3rd, you have to understand what the op-amp output does after V- = the new V+. (same as 2nd step, but the other polarity).
4th, you have to recognize the symmetry and repeatability of the 2nd and 3rd steps.

If you follow those steps, you will see how R1, R2, R3, C1 control the operation of the waveform generator, and end up with equations like shteii01 used to get his solution. If you can simulate like MikeML did, that can serve as a valuable sanity check, but you have to simulate correctly.

Regards,
Russell
 
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