PURPOSE:

The objective of this experiment is to learn to use the PSpice circuit simulator to study the transient and steady state AC behavior of circuits. The fundamentals of PSpice were covered in an earlier experiment. The emphasis in this experiment is on the time and frequency domain properties of circuits containing energy storage elements.

EQUIPMENT:

SPICE has been ported to personal microcomputers. PSpice is the PC version used at TU. It is marketed by OrCAD. SPICE is discussed in several textbooks with examples and appendices. CLICK HERE to download the free student version of PSpice used for this class.

GENERAL THEORY:

The general concept of simulating a circuit using PSpice is described in Experiment #4 Introduction to PSpice. DC or time invariant analysis of circuits is emphasized in the introductory exercises where transfer curves of output verses input or solutions at a fixed source value are obtained. There are two other modes of analysis for SPICE circuit simulation:

TRAN = transient or time domain analysis where the output is a waveform as a function of time.

AC = steady state AC or frequency domain analysis where the output is phasor values as a function of frequency.

TIME DOMAIN ANALYSIS:

The transient analysis requires at least two parameters: tstep and tstop. The total time duration for the analysis is specified by tstop. This value should be 5-6 times the RC time constant for todays lab. Tstep should be a small fraction of a time constant to ensure enogh details, but large enough to prevent generating excessive data values. The PROBE graphical output is highly recommended for displaying the waveform output of transient analyses. The waveform type and parameters of time varying sources must also be specified.

FREQUENCY DOMAIN ANALYSIS:

The frequency domain analysis requires four arguments. The sweep type parameter can be linear with equally spaced frequency points or logarithmic. There are two logarithmic options; octaves (factors of 2) or decades (factors of ten). The parameter points specifies the total number of points for a linear sweep, or the number of points per octave or decade for a logarithmic sweep. The last needed values are the starting and ending frequencies. The PROBE graphical output is very useful for viewing frequency sweep results

PROCEDURE:

1. Enter the schematic for the circuit of Figure 1. The voltage source to use is a Vsrc. Using AC analysis, sweep the frequencies from 10Hz to 100KHZ using 100 points per decade.
2. Execute the simulation using PSpice.
3. Plot the normalized magnitude of V_C and V_R as functions of frequency, for a frequency range of 10 to 100KHz.. Sketch the curve in your notebook.
4. Plot the phase of the current versus the frequency and sketch it in your notebook. Indicate if the current leads or lags. Note: In Pspice IP(R1) displays the phase of the current phasor through R1.
5. Change the previous schematic and find the current phasor through R1 for the following resistor values: 2.8K, 1.6K, 920 at the frequency of 1.0 KHz.
6. Enter the schematic for figure 1. Use a Vpulse source with the following attributes:
   • v1=0 . v2=5.0 td=0
   • tr=1n tf=1n pw=11m
   The analysis setup should be a transient from 0 to 1.5 milliseconds with a time step of 1 microsecond.
7. Execute the simulation using PSpice.
8. Plot Vc . Calculate tau, and C from the plot given an ideal Resistor using the 90%-10% method, discussed at the start of class. Record these values in your notebook.
9. Repeat the previous three steps for each of the following resistor values (3.3K and 4.7K) (Hint: Max voltage will remain 5.0V.)
10. Use PSpice to generate a graph of the voltage across the resistor, capacitor and inductor for figure 2. The voltage source is a Vpulse with:
    v1=0 v2=2.5 td=0 tr=1n tf=1n pw=11m
    The simulation should be a transient with the time of 0 to 250 microseconds and a time step of 0.1 microseconds. Include a labeled graph of all three voltages.
11. (Analysis) What does it mean when a voltage is negative in Pspice?
12. Repeat the previous step for figure 3. Use a simulation time of 500 micro-seconds.
13. (Analysis) How are the phase of V_L and V_C related? Why?