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#### bhl3302

##### Full Member level 6

Hi guys,I am trying to simulate a simple RC circuit using a step voltage source. The amplitude of the voltage is 28V. But when I use the transient analysis to simulate, the amplitude of the voltage is larger than the power supply.And the amplitude of the node of the source is not the value I set. So does any one know what is the problem? The circuit and the simulation result are given in the attachment, thank you so much!

#### Mazz

This is really strange.
The green circles in your schematic should be warnings, check & correct them, maybe the simulator will work.

Mazz

#### kender

setting vpulse pspice

I think, your pulse width (PW) is 100s. Your time axis, however, goes only to 10s

#### bhl3302

##### Full Member level 6

kender said:
I think, your pulse width (PW) is 100s. Your time axis, however, goes only to 10s
Thank you man, but if what I want is just a step signal from 0 to 28V and the simulation time is 10s, how can I set the Vpulse? Thank you so much!

#### kender

td for pspice vpulse

bhl3302 said:
... if what I want is just a step signal from 0 to 28V and the simulation time is 10s, how can I set the Vpulse?
As far as I remember, TD is a delay of the 1st pulse. If you set TD = 5, then your step will arrive at 5 seconds. Right now you have TD = 0.01, and you can actually see a step on the plot, but it's pathologically close to the beginning of time.

#### Mazz

The problem is that, for an indipendent source voltage, you NEVER should have a different voltage.
I tried to reproduce the same effect in Orcad, with same schematic, but, in my case (obviously), it works properly.
I cannot know what those warning are from, check them (or report them here...)
Also, did you modify in some way default simulator options?

Mazz

#### bhl3302

##### Full Member level 6
creating step voltage in schematic in orcad

Mazz said:
The problem is that, for an indipendent source voltage, you NEVER should have a different voltage.
I tried to reproduce the same effect in Orcad, with same schematic, but, in my case (obviously), it works properly.
I cannot know what those warning are from, check them (or report them here...)
Also, did you modify in some way default simulator options?

Mazz

Thank you Mass for your help. But I still don't know what you mean I never should have a different voltage? I think the default simulation options is fine. Could you take a picture of what you set in the Vpulse in order to get a step signal from 0V to 28V? Thank you so much!

kender said:
bhl3302 said:
... if what I want is just a step signal from 0 to 28V and the simulation time is 10s, how can I set the Vpulse?
As far as I remember, TD is a delay of the 1st pulse. If you set TD = 5, then your step will arrive at 5 seconds. Right now you have TD = 0.01, and you can actually see a step on the plot, but it's pathologically close to the beginning of time.

Thank you man for your explanation. But actually what I want to get is a very fast time, just like plug in the power suddenly. That is why I set the rising time so short. And my coufusion is that even though I set 28V, the amplitude in the simulation is much larger than that, so do you have any comment?Thank you so much!

#### Mazz

Sorry, I wasn't clear enough.
I mean that, if you use an indipendent voltage source with level V1, you will have exactly V1, no way.

I have copied EXACTLY your schematic, but in my case works properly.

Mazz

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