In PSPICE, the transient analysis option is used to do both steady and transient analysis of
circuits. This can involve both AC and DC signal sources. Steady-state AC time-domain
results are obtained by the same setup as for transient analysis. Let’s try it out.
1. Start a new project called “boing” and build the following schematic into it. (Make sure to
completely close the previous project).
Place the two voltage probes by clicking the probe button on the toolbar. Note the color of each probe; it will match the color of the trace in the PROBE readout during simulation. The source used is called “VPULSE” and the parameters on the source have the following meanings:
• V1 is the “off” voltage
• V2 is the “on” voltage
• The simulation begins with the source in the OFF state. TD is the time delay in seconds before the pulse turns on.
• TR and TF are the rise and fall times of the step function.
• PW is the pulse width (how long the source stays “on” after TD has passed.)
• PER is the period. Enter 0 for a one-shot pulse, or a non-zero period for the pulse to be periodic.
2. Build a new simulation profile called “transient” and make it look like this:
***“Run to time” says how long to run the simulation. 10 seconds is forever in the world of circuits, but this one is special.
***“Start saving data after 0 seconds” means to use all simulation results starting with time = 0. Entering a non-zero value causes initial data points to be discarded.
*** “Maximum step size” is a very important setting. It specifies how often PSPICE will recalculate the circuit parameters during simulation. If you’re expecting sinusoids to look good, you need at least 100 or more calculations for each sine wave period.
3. Press the F11 key. (Warning: Stand several feet back from the circuit when doing this!)
You should get the following display:
4. Try replacing the DC pulse source in the circuit with an AC signal source and repeat the
analysis again. You might want to change the “Run to time” in the analysis profile to 20
seconds. The circuit looks like this:
For the VSIN signal source, the parameters have the following meanings:
• VOFF is the DC offset
• VAMPL is the peak voltage of the sine wave
• FREQ is (you guessed it), the frequency of the signal in Hz.
You can set other parameters of the VSIN source by double-clicking the body of the part. You’ll get a complete listing of the settable parameters and their values.
#PSPICE Seminar / DeVry KC – Spring 2002