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EXPERIMENT NUMBER 2
PSPICE RC, RL, and RLC Simulations
Preface:
Preliminary exercises are to be done and submitted individually.
Laboratory simulation exercises are to be done in individually.
Laboratory hardware exercises are to be done in groups.
Work done in notebooks to be submitted individually.
The laboratory notebooks to be submitted immediately following the laboratory.
For this laboratory simulation exercise, students must submit the individual work done in
their laboratory notebooks. This work in the notebooks may be similar, but each student
will be tested individually in the practical examination.
This laboratory does not have any technical memorandum to be submitted. Later on, you
will need to submit individual technical memorandums that will be evaluated
individually.
The laboratory notebooks must include all settings, steps and observations in the
exercises. All statements must be in complete sentences and all tables and figures must
have a caption.
Review the guidelines for plagiarism to be aware of acceptable laboratory and classroom
practices.
Understanding the use of simulation tools and being able to operate these programs well are
fundamental for Electrical and Computer Engineers. The use of PSPICE to handle transient
behavior in circuits is relevant to many areas of practice.
Objectives:
To learn how to create RC, RL, and RLC circuit models in PSPICE.
To learn how to simulate models for transient analysis of source-free circuits.
References:
PSPICE experiments in EE 152 and PSPICE Tutorials (See departmental website)
Background:
PSPICE can be used to calculate transient voltages across components and transient currents
through components. To illustrate this, we will build RC, RL, and RLC circuit networks.
Preliminary:
(Work on separate paper and turn in at the beginning of the laboratory session.)
Sketch a circuit diagram with a resistor R and a capacitor C. No sources are included. Label
the voltage across C as V1 and the current through the resistor R as I1. (A-1) Derive the
theoretical first-order differential equation for voltage V1 and the associated characteristic
equation. (A-2) Give the natural response for the transient voltage V1 for t>0 s in terms of A
(constant to be determined), R1, and C. (A-3) Determine the theoretical expression for the
constant A if the initial value of the voltage V1 at t = 0 s is V0.
Sketch a circuit diagram with a resistor R and an inductor L. No sources are included. Label
the current through L as I1 and the voltage across the resistor R as V1. (B-1) Derive the
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theoretical first-order differential equation for current I1 and the associated characteristic
equation. (B-2) Give the natural response for the transient current I1 for t>0 s in terms of A
(constant to be determined), R1, and L. (B-3) Determine the theoretical expression for the
constant A if the initial value of the currentI1 at t = 0 s is I0.
The natural response of first-order circuits is of the form A exp(-t/ ) where is the time
constant. For t = , the natural response has decreased by exp(-1) = 0.3679. (C-1) Give an
expression in terms of R and C for the in the prior RC circuit. (C-2) Give an expression in
terms of R and L for the in the prior RL circuit.
Sketch a circuit diagram with three parallel elements: a resistor R, a capacitor C, and an
inductor L. No sources are included. Label the voltage across C as V1 and the current
through the inductor L as I1. (D-1) Derive the theoretical second-order differential equation
for voltage V1 and the associated characteristic equation. (D-2) For this case, the damping
coefficient is = (1/2R)√(L/C). Show the condition on R in terms of L and C for the circuit
natural response to be underdamped. (D-3) Sketch the underdamped response.
Equipment:
PSPICE simulation program in the CLC.
Experimental Procedure:
(Record specifics in the Laboratory Notebook.)
1. Use PSPICE to create a circuit model with a resistor R and a capacitor C using values given
by the Laboratory TA (R =
470
and C =
10
µF.
A resistor can be
obtained by typing “r” in the Recent Parts Box as shown in Figure 1, and a capacitor can be
obtained by typing “c” in the box. Place a 5 V DC voltage source in front of the resistor.
Connect the components like those shown in Figure 4. Place the GND connection and add a
voltage probe for the capacitor as shown.
Recent Parts
Box
Analysis
Setup
Voltage
Probe
Parts
Browser
Simulate
Add
Wire
Figure 1 - PSPICE Setup Screen
The transient analysis is setup by clicking the Analysis Setup box as shown in Figure 1 and
then clicking the Transient box as shown in Figure 2.
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Figure 2 - Analysis Setup Dialog Box
After clicking the Transient box, another dialog box will open. In this box, there are two
places information must be entered to simulate the transient solver. One is the Print Step and
the other is the Final Time (see Figure 3).
Figure 3- PSPICE .TRAN Setup
The Final Time should be six times the RC time constant. Once the Final Time is found, a
Print Step can be calculated by dividing the Final Time by 100. By using this many points,
we will gain a smooth curve. If a smoother curve is desired, more points should be added.
To shorten the length of the simulation time, fewer points may be added at the expense of the
curve becoming grainy. Your circuit should now look like the one shown in Figure 4.
Figure 4– RC Circuit for Experiment
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The initial conditions for a capacitor must be set for a Transient Simulation. This setting is
accomplished by double clicking on the capacitor to open up the dialog box which lists the
capacitors attributes as shown in Figure 5. The initial condition of the capacitor is labeled
“IC=” and is left blank by default. Set the initial condition to 0 volts to simulate a circuit
where the capacitor has no charge on it.
Initial
Condition
Figure 5 - Capacitor Attributes
Simulate the circuit by clicking the Simulate the icon (Refer to Figure 1).
Save the schematic and the transient response.
(Your laboratory notebook should list the steps, give a table of the values for R, C, and the
initial conditions, and include a printout of the PSPICE schematic and transient response.)
Q1: Calculate the time constant with the given values for R and C using the theoretical
expressions derived for the preliminary and compare it to the simulated value. Do they
match?
2. Use PSPICE to create a source free circuit model with a resistor R and an inductor L using
values given by the Laboratory TA (R =
and L =
H. Add a current
probe for the inductor. The initial condition for the inductor must be set like the capacitor in
step 1 (Inductor needs to be initialized with a value above 0).
Simulate the circuit. Save the schematic and the transient response.
(Your laboratory notebook should list the steps; give a table of the values for R, L, and the
initial conditions; and include a printout of the PSPICE schematic and transient response.)
Q2: Calculate the time constant with the given values for R and L using the theoretical
expressions derived for the preliminary and compare it to the simulated value. Do they
match?
3. Use PSPICE to create a circuit model with a parallel resistor R, capacitor C, and inductor L
using values given by the Laboratory TA
(R =
,C=
F, and L =
H. Add a voltage probe for
the capacitor. The initial condition should be set as before (Either capacitor or inductor
needs to be initialized above 0).
Simulate the circuit. Save the schematic and the transient response. Zoom in the transient
response and find resonant frequency.
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(Your laboratory notebook should list the steps; give a table of the values for R, L, and the
initial conditions; and include a printout of the PSPICE schematic and transient response.)
Q3: Calculate the damping coefficient with the given values for R, C, and L using the
theoretical expressions in the preliminary. Is the circuit underdamped or overdamped?
Does the transient response behave as expected?
4. Modify the RLC circuit model by changing the value of R (keep the same values of C and L).
If the prior transient response was underdamped use an R giving an overdamped response. If
the prior response was overdamped use an R giving an underdamped response. Simulate the
circuit. Save the schematic and the transient response.
(Your laboratory notebook should list the steps, give the new value for R and include a
printout of the PSPICE schematic and the transient response.)
Technical Memorandum:
A Technical Memorandum is not required for this laboratory experiment.