How do I Simulate a simple RC Circuit using Multisim?

Status
Not open for further replies.

fouadalnoor

Member
Hello guys, I have been trying to simulate a simple 30k resistor with a 100uF capacitor with a 9v supply for a while now.

From what I know theoretically the capacitor should reach about 8v in 7 sec. How come the simulation only shows the 9v on the oscilloscope as soon as I start the simulation?

(Screen shot below)
 

Attachments

  • 2.jpg
    471.8 KB · Views: 2,252
It's not something you would know, but the simulation normally calculates the steady-state DC operating point (with inductor and capacitor values = 0) of the circuit before doing the transient simulation. And the steady-state value of the capacitor voltage is 9V.

There are two possible solutions to this:

1. There should be an option to have it not calculate the DC operating point, or alternately set the initial voltages to zero (I believe in the Analysis Options).

2. You can use a time-delay (TD) switch to connect the voltage to the circuit after the start of the simulation.

I prefer 2 because it allows you to look at the initial conditions of the circuit before you see the transient.
 
All Spice derivatives, including LTSpice and most likely Multisim, do an initial "DC Bias" solution before commencing a "Transient" solution. During the Bias solution, the capacitor is assumed to be charged to the supply voltage. If you want to see the RC charge-up, you will have to name the node between the resistor and the capacitor, say RC, and put in an Initial Conditions statement, like .IC V(RC) = 0 to force that node to start from zero.
 
I tried to simulate it using the TD switch though that failed... umm I still don't know how to set the initial voltage to 0. DO you guys mind just showing me how to do the stuff step by step?
 
Here are two different ways to do it LTSpice. A third way is to use the "StartUp" option on the .Tran line. There are others...
 

Attachments

  • DF50.png
    40 KB · Views: 446
fouadalnoor said:
I know that it works now, but its soooo slow... il take a look at that manual...
Click to expand...
Here is my simulation with a TD switch using Electronic Workbench, which is an old version of that used in Multisim.

The simulation time was about 8 seconds, so the simulation time is close to real time.
 
Last edited:
Mikebits said:
Where did you get the battery, I don't see that in my lib?
Click to expand...

It is just an alternate symbol for a voltage source. I use it to signify that the voltage is not changing... Look under Misc in the pop-up list of standard symbols.
 
Status
Not open for further replies.

Similar threads

  • Question
Using PIC16F1939 and designing a circuit around it.
Replies
9
Views
2K
Fluffyboii
Z
  • Question
How to power on this weird circuit?
Replies
4
Views
264
carbonzit
C
L
  • Question
How to make a Elektrical Diagram Steinmetz Circuit Delta 3 phase motor
Replies
0
Views
958
Lucw
L
C
  • Question
a question I don't understand about the diode
Replies
7
Views
3K
Diver300
D
1
  • Question
Internal corrosion on a circuit?
Replies
10
Views
2K
1-3-2-4
1
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…