Transient Analysis in PSPICE

ECE 240 – Electrical Engineering Fundamentals PSPICE Tutorial 2 Transient Analysis in PSPICE This tutorial describes the transient analysis in PSPICE. A. Transient Analysis of a Circuit In this section of the tutorial, you will learn to perform a transient analysis on a circuit. The transient analysis is always used when you want to view a graph of a voltage or current as a function of time. Even if the voltages are DC as in the previous tutorials, transient analysis must be used to view a graph of the output versus time. R1 R2 2K 3K V1 10 R3 5k 0 Figure 1. Circuit for PSPICE Simulation Setting up the transient analysis 1. For this part we will simulate the circuit as shown in figure 1. Open a new PSPICE project and enter this circuit as you have done previously. 2. Select PSPICE à New Simulation Profile. Name the profile "transient". Select Time Domain (transient) for the Analysis type. There are several other important settings for the transient analysis. Run to time is the length of time that the simulation will run. In general you select this value to be the maximum value that you want to display on the time axis. In this case enter 0.5 (stands for 0.5 S). 3. Do not change the default setting of zero for the time that the data starts being saved. 4. Click OK. Setting Probes Before running the simulation, we need to mark the voltages and/or currents that we want to display with probes. Select PSPICE à Markers à Voltage Level, and place the probe that appears at the top of the 5KΩ resistor. Running and Displaying the Results of the Simulation Run the simulation. This time a display window will open and a graph of the resistor voltage will appear. Of course, since this is a DC circuit, all we see is a straight line, or constant voltage. Applying a Sinusoidal Input Signal A variety of input signals can be applied to your circuit in the transient analysis. In this section, we will change the DC source to a sinusoidal input source. Two sinusoidal sources can be used in PSPICE. We will be using the VSIN source. This is the one that must be used when you are plotting a graph with time as the x-axis variable. Later in the course you will learn more about the VAC input used for the AC analysis. 1. Click on the VDC source. Press the delete button to remove it from your circuit. 2. Select Place à Part à VSIN 3. Place this part in the space left by the removal of the DC source. Fix connections as necessary. 4. There are three parameters that needs to be set for this voltage source: VOFF, VAMPL, and FREQ. By double clicking on any one of them a box will appear in which you can enter the values. Set the values as follows: VOFF = 0 (this is the DC offset of the sinusoidal source) VAMPL = 1 (this is the peak amplitude of the sine wave) FREQ = 10 (this is the frequency of the sine wave in Hz) 5. Re-run the transient analysis that you set up earlier. The display should now show a graph of a sinusoidal voltage. Confirm that this is the value you expect to see. Using the Cursor 1. The cursor is used to mark a point on the plot you have generated and read values off the curve. Display the cursor by selecting: Trace à Cursor à Display. The Probe Cursor display box will appear. 2. Click on the plot and hold down the mouse button. Note that the cursor moves along with the mouse and the display of the x and y axis values appear in the cursor box. 3. Move the cursor to any point on the graph. The Probe cursor box will display the value of the time and voltage at that point. When this screen is printed, the cursor values will also appear. Pulse Waveform A voltage pulse or pulse train can be applied as an independent source in PSPICE using the VPULSE element. VPULSE has seven parameters that describe its shape as shown in figure 2. TR TF TR TF V2 PW PW V1 TD PER Figure 2. Parameters of VPULSE PER