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424 ⏐⏐⏐ CAPACITORS
more than one cursor is used. By moving the cursor to 200 ms, we find
that the magnitude (A1) is 19.865 V (in the Probe Cursor dialog box),
clearly showing how close it is to the final value of 20 V. A second cursor
can be placed on the screen with a right click and then a click on the
same V1(C) on the bottom of the screen. The box around V1(C) cannot
show two boxes, but the spacing and the width of the lines of the box
have definitely changed. There is no box around the Pulse symbol since
it was not selected—although it could have been selected by either cursor.
If we now move the second cursor to one time constant of 40 ms,
we find that the voltage is 12.633 V as shown in the Probe Cursor dialog
box. This confirms the fact that the voltage should be 63.2% of its
final value of 20 V in one time constant (0.632 � 20 V � 12.4 V). Two
separate plots could have been obtained by going to Plot-Add Plot to
Window and then using the trace sequence again.
Average Capacitive Current As an exercise in using the pulse
source and to verify our analysis of the average current for a purely
capacitive network, the description to follow will verify the results of
Example 10.13. For the pulse waveform of Fig. 10.59, the parameters
of the pulse supply appear in Fig. 10.79. Note that the rise time is now
2 ms, starting at 0 s, and the fall time is 6 ms. The period was set at
15 ms to permit monitoring the current after the pulse had passed.
Simulation is initiated by first selecting the New Simulation Profile
key to obtain the New Simulation dialog box in which AverageIC is
entered as the Name. Create is then chosen to obtain the Simulation
FIG. 10.79
Using PSpice to verify the results of Example 10.13.