#### Frenetique

- Sep 25, 2016

- 3

- Joined
- Sep 25, 2016

- Messages
- 3

Hi everyone !

I am trying to design a triangular wave generator with LTSpice in order to learn a bit how to use this simulator.

The goal is to have a triangular signal with a frequency of 20kHz and centered around 5V with an output voltage dynamic of 2/3 of the single 10V supply (so the signal goes from 1.66V to 8.33V, centered around 5V).

The theoretical concept is fairly simple; a Schmitt trigger's output is sent to an integrator (square to triangle) and the output from the integrator is looped back to the trigger. I managed to do it with theoretical componant (universal op amp) but I can't do it with "real" componant (LT library). Basically the whole system is never oscillating.

I isolated each part and simulated one after another and there are some behaviours, I believe not related to the simulation but more with the real charcteristics of op amps, that I don't understand.

theory_triang_generator.png shows the schematic for the theoretical circuit.

real_triang_generator.png shows the schematic for the true circuit.

I also attached the three simulated circuits, namely the whole triangle wave generator, an integrator and a Schmitt trigger. Each time there is the equivalent with the theory.

Consider that I know the theoretical model of an op amp but I'm not at ease with real ones and with their flaws.

Therefore my questions are:

- Why does the integrator kind of saturate like it does (tips of triangles are cut and flat, see true_integrator.asc) ?

- Why the Schmitt trigger has a high voltage that is dropping (see real_schmitt_trigger.asc) ?

- Why my design with real LT componants of the triangle wave generator won't start (see Triangular_wave_generator.asc) ?

I know this is a lot of questions. I thank you in advance for your enlightenments.

Best regards.

I am trying to design a triangular wave generator with LTSpice in order to learn a bit how to use this simulator.

The goal is to have a triangular signal with a frequency of 20kHz and centered around 5V with an output voltage dynamic of 2/3 of the single 10V supply (so the signal goes from 1.66V to 8.33V, centered around 5V).

The theoretical concept is fairly simple; a Schmitt trigger's output is sent to an integrator (square to triangle) and the output from the integrator is looped back to the trigger. I managed to do it with theoretical componant (universal op amp) but I can't do it with "real" componant (LT library). Basically the whole system is never oscillating.

I isolated each part and simulated one after another and there are some behaviours, I believe not related to the simulation but more with the real charcteristics of op amps, that I don't understand.

theory_triang_generator.png shows the schematic for the theoretical circuit.

real_triang_generator.png shows the schematic for the true circuit.

I also attached the three simulated circuits, namely the whole triangle wave generator, an integrator and a Schmitt trigger. Each time there is the equivalent with the theory.

Consider that I know the theoretical model of an op amp but I'm not at ease with real ones and with their flaws.

Therefore my questions are:

- Why does the integrator kind of saturate like it does (tips of triangles are cut and flat, see true_integrator.asc) ?

- Why the Schmitt trigger has a high voltage that is dropping (see real_schmitt_trigger.asc) ?

- Why my design with real LT componants of the triangle wave generator won't start (see Triangular_wave_generator.asc) ?

I know this is a lot of questions. I thank you in advance for your enlightenments.

Best regards.