It's a long time I don't do some calculations .... I know it's simple but I would precision because Idon't find the same result between simulation and calculation;
1)


I want to know how calculate the time when Vs2 : 0V to 3.5V (charge) and the time when Vs2 5V to 1.5V.
Ve = 0-5V (simple square signal)

2) What is the difference between these two schemes (same calculations?):
R//C


R + C


Thank you for your help

 

hi B,
Welcome to AAC.
Your question is a little vague.?

If you are asking the difference between the top circuit and the middle circuit, its the presence of R5 [140R]

The bottom circuit is a simple RC circuit, what is the question.?

Post your asc sim file and calculations.
E

 

Do you want to calculate the charge and discharge?

 

Thanks for your quick answer.

There are 2 questions/points:
1) Yes, calculation of the time (formula)=> charge and discharge at a given voltage
2) Question on the difference between the two RC circuits => same time for charge and discharge in the two cases?

 

hi B,
Have a check thru this PDF, ask if you have a problem.
If you have any LTSpice asc files for this query please attach to your post.
E

 

See

 

Thank you.
1)
Charge
With calculation:
Vf=4.85V (divider)
Vi=0V
Vt= 3.5V

T(VIH)=ζ x ln((Vf-Vi)/(Vf-Vt))
ζ = R5
T(VIH) = 0.590ns => simulation of Bordodynov = 0.607ns

Discharge
With calculation:
Vf=0V
Vi=4.85V
Vt= 1.5V

T(VIH)=ζ x ln((Vf-Vi)/(Vf-Vt))
ζ = R5//R2
T(VIH) = 0.557ns => simulation of Bordodynov = 5.56ns

What is wrong?

 

The discharge is ok => T(VIH) = 0.557ns => simulation of Bordodynov = 0.556ns. Sorry I can't edit my message....