OrCAD PSPICE trouble

[BradBrigade]

Hello,

I'm new to PSPICE and it seems I need a little help. I have OrCAD 10.
I'm trying to simply put a resistor in series with a capacitor and
connect a 10V power supply (VDC). I set a voltage tester between the
resistor and capacitor and when I run a transient alanysis, I get a
straight line at 10V. No matter what time values, no matter what
values I use for the resistor and capacitor, I ALWAYS get a straight
line.

I changed the VDC to a VSTIM and set up a square wave. Sure enough, on
each pulse, I see a curved rise and a curved fall. Why don't I see a
curved rise at the start of the simulation with VDC?? I don't want to
use a square wave generator, I just want a simple voltage source like a
battery. What is going on??

Any help is appreciated! Thanks!
-Brad

 

[Jim Thompson]

On 17 Apr 2006 10:56:11 -0700, "BradBrigade" <sizzlefist@hotmail.com>
wrote:

Hello,

I'm new to PSPICE and it seems I need a little help. I have OrCAD 10.
I'm trying to simply put a resistor in series with a capacitor and
connect a 10V power supply (VDC). I set a voltage tester between the
resistor and capacitor and when I run a transient alanysis, I get a
straight line at 10V. No matter what time values, no matter what
values I use for the resistor and capacitor, I ALWAYS get a straight
line.

I changed the VDC to a VSTIM and set up a square wave. Sure enough, on
each pulse, I see a curved rise and a curved fall. Why don't I see a
curved rise at the start of the simulation with VDC?? I don't want to
use a square wave generator, I just want a simple voltage source like a
battery. What is going on??

Any help is appreciated! Thanks!
-Brad

(1) If you want to observe a transient response you HAVE TO USE a
transient source.

(2) Use VPULSE

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

Old Latin teachers never die...they just decline

 

[BradBrigade]

I see. That seems pretty weird. How do I know the difference between
a transient source and a source like VDC (whatever it's called). There
is nothing in the place part dialog that suggests that these two parts
are different in that respect.

Well, at least now I know I'm not doing something wrong when I use
something other than VDC.

Thanks for the help, much appreciated!
-Brad

 

[engr4fun]

Hi,

Disable the DC bias point calculation (I don't have that version so I'm
not sure how they do it). At the beginning of SPICE transient
simulations, a DC bias point is calculated where the capacitors are
treated as open circuits. It uses this calculated point as the first
point of the simulation. When this calculation is disabled, all
voltages and currents (not specified with an IC statement) start at
zero, and you should get the curve you are looking for.

Alex

 

[René]

On 17 Apr 2006 10:56:11 -0700, "BradBrigade" <sizzlefist@hotmail.com>
wrote:

Hello,

I'm new to PSPICE and it seems I need a little help. I have OrCAD 10.
I'm trying to simply put a resistor in series with a capacitor and
connect a 10V power supply (VDC). I set a voltage tester between the
resistor and capacitor and when I run a transient alanysis, I get a
straight line at 10V. No matter what time values, no matter what
values I use for the resistor and capacitor, I ALWAYS get a straight
line.

I changed the VDC to a VSTIM and set up a square wave. Sure enough, on
each pulse, I see a curved rise and a curved fall. Why don't I see a
curved rise at the start of the simulation with VDC?? I don't want to
use a square wave generator, I just want a simple voltage source like a
battery. What is going on??

Any help is appreciated! Thanks!
-Brad

I would use the IC ("Initial Condition") parameter available in the
capacitor property editor field. Just set it to "0". Otherwise it
starts to simulate the situation departing from the bias calculation
situation.

--
- René