Re: gEDA-user: How to do transient analysis?

[Daniel Nilsson <daniel@xxxxxxxxxxxxxxx>]

On Sat, Apr 09, 2005 at 08:39:14AM -0600, David Logan wrote:
> Daniel Nilsson wrote:
> 
> >On Fri, Apr 08, 2005 at 05:34:14PM -0600, David Logan wrote:
> > 
> >
> >>What would be the best way to do transient analysis using geda? I have 
> >>pspice instructions, which are easy enough. I just define a circuit like:
> >>
> >>gnd -> IDC -> t_Close (t=0) -> R -> L -> gnd. Then I go into "Transient 
> >>analysis" setup, set "Print Step" and "Final Time", and I get a graph of 
> >>my capcitor voltage or inductor current.
> >>   
> >>
> >
> >I'm not sure I understand what your circuit is supposed to do, are you
> >sending a DC current through an inductor ? That should not produce
> >anyting interesting in simulation at all...
> > 
> >
> It actually does produce something interesting between t=0 and t=L/R, 
> because current changes at a rate of If+(Ii-If)e^(-t/(L/R)), and the 
> voltage changes at L*di/dt of that.

Ok, I must not understand your initial circuit description then or
potentially how pspice does this... The way I read your description
was that you connected a current source into a switch, and the switch
closed at time=0. I don't know how pspice does this (I use HSPICE
normally and I can't remember much of pspice any longer), but one idea
is that pspice solves the DC condition with the switch open and the
starts the transient analysis at time step 0 with the switch closed ?

If so, how does it figure out the DC voltage at the output node of the
current source if there is no DC path to ground from this node (the
switch is open) ?

There are switches available in ngspice as well, see section 3.1.9 and
3.1.10 in online help  (type help at the ngspic prompt) or search for
switch in the manual.

-- 
Daniel Nilsson