1. EENG 2920: Circuit Design and Analysis Using PSpice Class 4: Transient Analysis (2)
Oluwayomi B. Adamo
Department of Electrical Engineering
College of Engineering, University of North Texas

2. Switches
PSpice allows the simulation of a special kind of switches, whose resistance varies continuously depending on the voltage or current.
When the switch is on, the resistance is RON, and when it is off, the resistance is ROFF.
Switch
On state
Off state
EENG 2920, Class 4

3. Voltage-Controlled Switch
The symbol for a voltage-controlled switch is S. The name of this switch must start with S, and the general form is:
S<name> N+ N- NC+ NC- SNAME where N+ and N- are the two nodes of the switch. The current is assumed to flow from N+ through the switch to node N-. NC+ and NC- are the positive and negative nodes of the controlling voltage source. SNAME is the model name of the switch.
Model parameters for voltage-controlled switch (Table 4.8, page 113)
VON: control voltage for ON state, unit: V, default: 1.
VOFF: control voltage for OFF state, unit: V, default: 0.
RON: ON state resistance, unit: Ohms, default: 1.
ROFF: OFF state resistance, unit: Ohms, default: 1E6.
Note: RON and ROFF must be greater than zero and less than 1/GMIN. The default value for GMIN is 1E-12 mhos. The value of ROFF should be as high as possible and that of RON should be as low as possible as compared to other components in the circuit.
The voltage-controlled switch device from “breakout.olb” can be edited and new models can be defined in the same way as resistor. For example,
.MODEL Smod1 VSWITCH (RON=0.5 ROFF=10E6 VON=0.7 VOFF=0)
EENG 2920, Class 4

4. Current-Controlled Switch
The symbol for a current-controlled switch is W. The name of this switch must start with W, and the general form is:
W<name> N+ N- VN WNAME where N+ and N- are the two nodes of the switch. The current is assumed to flow from N+ through the switch to node N-. VN is the voltage source through which the controlling current flows. WNAME is the model name of the switch.
Model parameters for voltage-controlled switch (Table 4.9, page 118)
ION: control current for ON state, unit: A, default: 1E-3.
IOFF: control current for OFF state, unit: A, default: 0.
RON: ON state resistance, unit: Ohms, default: 1.
ROFF: OFF state resistance, unit: Ohms, default: 1E6.
Note: The current through voltage source VN controls the switch. The voltage source VN must be an independent source, and it can have a zero or a finite value. Limitations on other parameters are similar to voltage-controlled switch.
The current-controlled switch device from “breakout.olb” can be edited and new models can be defined in the same way as resistor. For example,
.MODEL Wmod1 ISWITCH (RON=0.5 ROFF=10E6 ION=0.07 IOFF=0)
EENG 2920, Class 4

5. Time-Dependent Switches
Time dependent close switch: Sw_tClose
This switch is normally open; setting the closing time closes it.
Time dependent open switch: Sw_tOpen
This switch is normally closed; setting the closing time opens it.
From library:
The devices Sw_tClose and Sw_tOpen are from the library “eval.olb” in the lite version of Capture (the one you got with book)
The devices Sw_tClose and Sw_tOpen are from the library “ANL_MISC.olb” in the Capture CIS, the version in the EE Labs
Model parameters for time-dependent switches (Table 4.10, page 120)
TClose/TOpen: time at which switch begins to close/open. unit: s, default: 0.
ttran: time required to switch states from off state to on state (must be realistic, not 0), unit: s, default: 1us.
Rclosed: closed state resistance, unit: Ohms, default: 10mOhm.
Ropen: open state resistance (Ropen/Rclosed < 1E10), unit: Ohms, default: 1MEGOhm.
EENG 2920, Class 4

6. Example 4.7 Draw circuit as shown in the figure.
Vs is VSIN from “source.olb”
Parameters for SMOD:
.MODEL SMOD VSWITCH ROFF=10E9 RON=5M VOFF=0 VON=25M
Run simulation to obtain the result
Analysis type is Time Domain (Transient)
Run to time: 1ms
Max step size: 5us
Figure 4.7.1
EENG 2920, Class 4
Figure 4.7.2

7. Example 4.8 Figure 4.8.1 Draw circuits Run Simulation Figure 4.8.2
S1 is the Sbreak from “breakout.olb”
Model for SMOD:
.model SMOD1 VSWITCH RON=0.01 ROFF=10E5 VON=0.1 VOFF=0
Run Simulation
Transient Analysis
Run to time: 20ms
Max step size: 5us
EENG 2920, Class 4
Figure 4.8.2

8. Example 4.9 Run simulation Draw circuit W1 is from “analog.olb”
Analysis type: Time Domain (Transient)
Run to time: 160us
Max step size: 1us
Figure 4.9.1
EENG 2920, Class 4
Figure 4.9.2

9. Example 4.10 Run simulation Draw circuit
Sw_tClose is from “eval.olb” in the Lite version of Capture.
Sw_tClose is from “ANL_MISC.olb” in the Capture CIS version (the version in the EE Labs).
Run simulation
Run to time: 160us
Max step size: 1us
Figure
EENG 2920, Class 4
Figure

10. Example 4.11 Run simulation Draw circuit
Sw_tOpen is from “eval.olb” in the Lite version of Capture.
Sw_tOpen is from “ANL_MISC.olb” in the Capture CIS version (the version in the EE Labs).
Run simulation
Run to time: 100us
Max step size: 1us
Figure
EENG 2920, Class 4
Figure

11. (Your final circuit schematics)
Problem 4.22 (page 129)
Please note that the following changes have been made to the original problem
The control voltage of the voltage controlled switch S1 is Vc, i.e., the voltage across the capacitor.
Simulate the circuit and obtain the following result for the voltage across the capacitor C, i.e., Vc.
You need to include your final circuit schematics in your assignment report.
(Your final circuit schematics)
Figure P4.22.1
EENG 2920, Class 4
Figure P4.22.2

12. Assignment 4 Assignment is due next week before class.
Repeat and reproduce the results for Examples 4.7, 4.8, 4.9, 4.10, and 4.11, and Problem 4.22 on page 129 in the book.
Reproduce the figures on the previous slides and explain the functionality and the behavior of each circuit:
Figures 4.7.1, 4.7.2
Figures 4.8.1, 4.8.2
Figures 4.9.1, 4.9.2
Figures ,
Figures ,
Figures P4.22.1, P4.22.2
Assignment is due next week before class.
Compile all your results in a report and turn in the print-out of the document. See Class 1 notes for the report format.
EENG 2920, Class 4