Message-ID: <a122194d067751cf4d45af085e91cf10.squirrel@webmail.strucktower.com>
Date: Sat, 27 Oct 2012 19:51:55 -0700
Subject: [geda-help] Another new user question on ngspice- how to export plots, and using
 current
From: keitho AT strucktower DOT com
To: geda-help AT delorie DOT com
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Reply-To: geda-help AT delorie DOT com

Hi all-

I'm using ngspice on Linux/Debian. I guess the graphing/plots are done
using X11 by default? I haven't figured out how to export my graphs to
PNG's so that I can send them in emails to folks helping me learn. Is
there a way to do that, or do you recommend using a different program for
graphing the plots that provides that feature?

Second question: in general, I'm confused about the way ngspice handles
current. Just as an example, here's a trivial netlist of a circuit using a
current source to drive the base:

common-emitter amplifier
i1 0 1 dc
q1 2 1 0 mod1
r 3 2 5000
v1 3 0 dc 15
.model mod1 npn
.control
dc i1 0 50u 2u
run
plot v(2)
.endc
.end

Here's the output of display:

ngspice 2 -> display
Here are the vectors currently active:

Title: common-emitter amplifier
Name: dc1 (DC transfer characteristic)
Date: Sat Oct 27 22:39:55  2012

    V(1)                : voltage, real, 26 long
    V(2)                : voltage, real, 26 long
    V(3)                : voltage, real, 26 long
    i-sweep             : voltage, real, 26 long [default scale]
    v1#branch           : current, real, 26 long


The graph of this is the correct shape, but I'm confused about why it is
sweeping voltage rather than current. Can someone explain what's going on
here, or point to a tutorial that would help?

The above netlist if taken from, and is diagrammed at,
http://www.allaboutcircuits.com/vol_3/chpt_4/5.html

Thanks,
Keith Ostertag