Download Bias Point Calculations - CVL Wiki

PSpice Version 9.1 Schematics
Objective of Lecture
 Demonstrate how to use PSpice Schematics to
calculate node voltages and the currents flowing into
and out of nodes.
 Most circuit simulation packages use nodal analysis.
Download Instructions
 Instructions on how to download and install PSpice
are posted on the Virginia Tech ECE Computer and
Visualization Laboratory (CVL) website.
 http://computing.ece.vt.edu/wiki/PSpice_FAQ
After Launching PSpice Schematics
Select Draw/Get New Part, which will
cause a pop-up window to open with a list
of all of the parts available in the student
version of Schematics.
- Note that there is a key stroke shortcut
.
Pick a Part
Type the name of the part in the
box located by Part Name or
scroll through the list of parts and
click on the name of the one that
you want put into the circuit.
Then, click Place if you have more
parts to select or Place and Close
if this is the last part.
If You Know the Name of Your Part
You can type it in directly into the box below the Toolbar
Help and then hit Enter.
 Either way, a symbol for a dc battery will appear on the
schematic when you move your cursor on to it.




Left Click to place the part in a specific location on the
schematic.
Right Click to end the process of placing the part Vdc.
Control-R will rotate the part 90 degrees for each CNT-R.
Control-F will flip the part about a vertical axis.
Names of Components
Component
PSpice Name
Component
PSpice Name
DC voltage supply
Vdc
Resistor
R
DC current supply
Idc
Capacitor
C
Ground
gnd_earth
Inductor
L
Connect Parts
Click on the pencil.
Then click the pencil tip to
one end of a part and then to
the end of another part to
place a wire between them..
Save Your Schematic
 PSpice will not run a simulation unless your circuit is
saved.
 You can select any directory in which to save the .sch
file.

Note: You can send the .sch file to me if you need assistance
finding errors that prevent the simulation from running.
Select Type of Simulation
 Click on Analysis/Setup or the
button.
 Bias Point Detail should be clicked. If not, do so.
Ground
 A ground must be included in the circuit as the
program calculates all voltages with respect to this
point.
 Note: The first step that I identified in the lecture on
nodal analysis was to select one node as the reference or
ground, which means that the voltage at the node will be
set to 0V.
 A common error message in PSpice is that the ground is
not connected.

After verifying that you did place a ground in the circuit
schematic, make sure that a node (dot) connects ground to
the circuit.
Run the Simulation
 Click Analysis/Simulate or click on the
A pop-up window should
open, text should scroll by
in the bottom left box.
After “Simulation complete”
is printed, the run is
finished.
button.
To Display DC Values
 Click on Analysis/Display Results on Schematic and
enable the voltage and/or current display.
Node Assignment
 Click on the box containing the value of the node
voltage.
 The node associated with that voltage is changed to a
dashed line.
Direction of Current
 Click on the box containing the value of current
flowing at a node.
 An arrow will appear on the schematic, indicating the
direction that the program assigned to the flow of that
current.
Voltage Across Components
 Note that the calculation performed by PSpice is a
nodal analysis. The voltage dropped across a
component is the difference between node voltages.
Summary
 PSpice may be used to verify the calculations that you
perform to calculate the currents and voltages in a
circuit, but should not replace your own calculations.
 The results from PSpice should be the same as the
results that you obtain for the circuit when using nodal
analysis.
 The voltages and currents from nodal analysis can be
converted to the voltage drops and mesh currents used
in mesh analysis.