RC Dynamics

Load the series RC circuit in PSPICE file rc-trans.sch, Figure 21. Here,

$\begin{displaymath}v_{in} = 5 u(t) \ {\rm V} , \ \ \ v_C(0^-) = 2 \ {\rm V} . \end{displaymath}$

**Figure 21:** RC circuit.
$\begin{figure} \begin{center} \epsfig{file=images/clab3img1.eps}\end{center}\end{figure}$

**Figure 22:** RC transient waveform.
$\begin{figure} \begin{center} \epsfig{file=images/clab3img2.eps}\end{center}\end{figure}$

Exercise:

1.

Simulate the circuit and obtain the transient response of Figure 22 (capacitor voltage - add a voltage marker if necessary).

2.

From the graph, determine the time constant $\tau$ and the final DC steady state value.

You will need to estimate the initial slope of the waveform to determine $\tau$ as shown in Figure 23. Use two probe cursors to obtain data values.

Figure 23: RC transient waveform: estimation of time constant from straight line with slope equal to initial slope of waveform.
$\begin{figure} \begin{center} \epsfig{file=images/clab3img2a.eps}\end{center}\end{figure}$

3.

**Figure 23:** RC transient waveform: estimation of time constant from straight line with slope equal to initial slope of waveform.
$\begin{figure} \begin{center} \epsfig{file=images/clab3img2a.eps}\end{center}\end{figure}$

Experiment with different component values and record the effect on the time constant in a table. Determine an empirical relationship between the time constant $\tau$ and resistance R. Compare with theory.

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