how to model this schematic low pass filter in simulink?

having trouble converting this schematic to simulink 2023 version.

[Mathieu NOE]

simulink does not (yet) convert hardware schematics into filters... you have to write the filter TF first ....

[Marc]

What is the purpose of capacitor C113? That is not present for a low-pass Butterworth filter circuit.

Answer 1

[Fangjun Jiang]

If you have this toolbox

https://www.mathworks.com/products/simscape-electrical.html

[Mathieu NOE]

when I was student , or even at the beginning of my career , there was no simulation tool .

you had to write the equations by hand

[Marc]

I do have the simscape electrical toolbox, I was able to copy this schematic in simulink but the output of the opamp seems to be not working (The signal measured from X120 is identical to the input signal measured from the left of R86 resistor . The other thing is what is the purpose of the V173 and V174 diodes?

[Fangjun Jiang]

Good for you, @Mathieu NOE, to have that training! I can't figure out the equation but maybe can build a breadboard for it.

[Mathieu NOE]

@Fangjun Jiang

yeah, most of my young colleagues don't have a clue about analog electronics. It requires quite a bit of skills to properly design and test complex analog circuits. 40 years ago there was no spice or simscape simulators . Smoke was often the reward of bad design. You would learn the hard way.

@Marc

V173 and V174 ar clamp diodes . they protect the input from going above / below + and - supply voltages which could damage the OP amp.

Clamp Diodes: Principles, Functions, and Applications (elecsaler.com)

you can remove that to simplify your simulation as they come into play only for very large amplitude signals

[Marc]

@Mathieu NOE same thing with me when I was a student. This is my first time learning Matlab.

[Marc]

What would be the Vout equation for this circuit?