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University of Sharjah
Electrical and Electronics Engineering Department
0402203
Circuit Analysis I Laboratory
Experiment # 8
Introduction to PSPICE – Part II (Transient Analysis)
OBJECTIVES:
1. To learn the use of PSPICE for transient analysis of circuits.
2. To simulate circuits for transient analysis containing Sinusoidal, Square and Triangular
wave sources.
INTRODUCTION:
In PSPICE, transient analysis is generally used to examine the behavior of a waveform (voltage or
current) with time. To perform transient analysis on a circuit in PSPICE usually involves three steps:
1. Create circuit in Schematics and specify the source parameters
2. Set analysis parameters and simulate the circuit.
3. Obtain graphs using the PROBE.
1. Creating circuit in Schematics and specifying the source parameters
In order to run transient analysis on a circuit, the circuit must first be created using Schematics and the
source must be specified. PSPICE has several time-varying functions or sources. Sources used in the
transient analysis include:
 VSIN : Damped Sinusoidal Voltage
The VSIN source has the following attributes, which are illustrated in Figure 1
VOFF
= Offset voltage
VAMPL
= Amplitude
TD
= Time delay in seconds
FREQ
= Frequency in Hz
DF
= Damping factor
PHASE
= Phase in degrees
The attributes that you usually need to adjust are VOFF, VAMP and FREQ. Attributes TD, DF, and
PHASE are set to 0 by default but can be assigned other values if necessary.
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 VPULSE : Pulse Voltage Source
The VPULSE source has the following attributes, which are portrayed in Figure 2
TD
PW
=
=
V1
=
Low voltage
V2
=
High voltage
Initial time delay in seconds (usually 0)
TR
=
Rise time in seconds
TF
=
Fall time in seconds
Width of the top of the pulse in seconds
PER
=
Period in seconds
We can use VPULSE source to generate Square or Triangular waveforms by adjusting TR, TF and PW
appropriately. These attributes are assigned in relation with PER.
For Square wave with time period T (=1/f), these attributes can be set as
TR=1% of T ; TF=1% of T; PW=49% of T
For Triangular wave with time period T (=1/f), these attributes can be set as
TR=49.5% of T ; TF=49.5% of T; PW=1% of T
In addition to specifying the source to be used in Transient analysis, there may be need to set initial
conditions on capacitors and inductors in the circuit. To do so, DCLICKL the part symbol to bring up
the Part name dialog box, click IC= and type in the condition. The IC attribute allows for setting the
initial conditions on a capacitor or inductor. The default value of IC is 0. The attributes of open/close
switches (with part names Sw_tClose and Sw_tOpen ) can be changed in a similar manner.
2. Set analysis parameters and simulate the circuit.
After the circuit is drawn and the source is specified with its attributes, we need to add some
specifications for the transient analysis.
These specifications control the simulation time and the display of output variables.
► Final Time specifies how long the simulation should run. In other words, the
simulation runs from t=0 to t=Final Time.
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► Print Step refers to the time interval the print part will print out; it controls how
often simulation results are written to the output file. The value of Print Step can
be any number less than the Final Time, but it cannot be Zero.
► Step ceiling is an optional parameter that refers to the maximum time between
simulation points. A smaller value gives more points but takes more time.
After the circuit is drawn, the specifications for the Transient analysis are given, and the circuit is
saved, we are ready to simulate it. To perform transient analysis, we select Analysis/Simulate.
3. Obtain graphs using the PROBE
To simulate the circuit we select Analysis/Simulate. If there are no errors, the Probe window will
automatically appear. As usual, the time axis (or X axis) is drawn but no curves are drawn yet. Select
Trace/Add and click on the variables to be displayed.
 Use of Markers
An alternative way of displaying the results is to use markers. Although there are many types of
markers, we will discuss only voltage and current markers. A voltage marker is used to display voltage
at a node relative to ground; a current marker is for displaying current through a component pin. To
place a voltage marker at a node, take the following steps while in the Schematics window;
1. Select Markers/Mark Voltage /Level.
2. DRAG the voltage marker to the desired node.
3. CLICKL to place the marker and CLICKR to end the placement mode.
This will cause two things to happen immediately. The voltage marker becomes part of the circuit and
the appropriate node voltage is displayed by Probe.
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LAB WORK:
Example 1:
Using Transient analysis in PSPICE
simulate the circuit shown in Figure
3.
The
sinusoidal
source
has
amplitude 10Vp and frequency 1kHz.
Obtain the plot of the voltage across
the resistor for 5 cycles.
Figure 3 Circuit for Example 1
1. Run Schematics and draw the circuit as shown in Figure 3.
2. DBCLICKL the VSIN source to set the parameters. You need to set only the VAMP and
FREQ. Set VAMP to 10 and FREQ to 1000.
3. Set analysis parameters. Select Analysis/Setup/Transient to open up the Transient Analysis
dialog box. The value for Final Time will depend on how many cycles do you want to display.
For 5 cycles it should be
Final Time = 5*Period of 1 cycle = 5/Frequency = 5ms
Print Step = Final Time / 1000 = 5μs
And
Step Ceiling = PrintStep = 5μs
Figure 4 Setup for Transient Analysis
CLICKL OK/Close to accept specifications.
4.
Connect voltage markers as shown in Figure 3 to view the waveforms in Probe. Simulate the
circuit.
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Example 2:
Using Transient analysis in
PSPICE simulate the circuit
shown in Figure 5. The voltage
source is a square wave with
amplitude 10Vp and frequency
1kHz. Obtain the plot of the
voltage across the capacitor for
5 cycles.
10k
+
Vs
+
0.01  F
-
v(t)
-
Figure 5 Circuit for Example 2
1. Run Schematics and draw the circuit as shown in Figure 5.
2. Use VPULSE to obtain a square wave by adjusting the parameters. You need to set only
V1=-10; V2=10; PER=1m; TR=TF=1% of PER=0.01m; PW=49% of T=0.49m
3. Set analysis parameters as in example 1.
4. Connect markers to view input (source voltage) and output voltage (voltage across capacitor) in
Probe.
5. Run simulation. Don’t forget to connect the ground.
QUESTIONS
Q 1. Repeat example 1 for triangular wave with amplitude 10 Vp-p and 1kHz. Frequency.
Use VPULSE to generate triangular wave by supplying appropriate values to TR, TF
and PW.
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