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ELEC 2110 Experiment 9 1 of 9 EXPERIMENT 9 Problem Solving: First-order Transient Circuits I. Introduction In transient analyses, we determine voltages and currents as functions of time. Typically, the time dependence is demonstrated by plotting the waveforms using time as the independent variable. PSPICE can perform this kind of analysis, called a Transient simulation, in which all voltages and currents are determined over a specified time duration. To facilitate plotting, PSPICE uses what is known as the PROBE utility, which will be described later. As an introduction to transient analysis, let us simulate the circuit in Figure 1, plot the voltage vC(t) and the current i(t). Figure 1. The inductor and capacitor parts are called L and C, respectively, and are in the ANALOG library. The switch, called SW_TCLOSE, is in the EVAL library. There is also a SW_TOPEN part that models an opening switch. After placing and wiring the switch along with the other parts, the Schematics circuit appears as that shown in Figure 2. Figure 2. PSPICE schematic To edit the switch’s attributes, double-click on the switch symbol and the ATTRIBUTES box in Figure 3 will appear. Deselecting the Include Non-changeable Attributesand Include
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ELEC 2110 Experiment 9 2 of 9 System-defined Attributesfields limits the attribute list to those we can edit and is highly recommended. The attribute tCloseis the time at which the switch begins to close, and ttranis the time required to complete the closure. Switch attributes Rclosedand Ropenare the switch’s resistance in the closed and open positions, respectively. During simulations, the resistance of the switch changes linearly from Ropenat t = tCloseto Rclosedat t = tClose+ttran. When using the SW_TCLOSE and SW_TOPEN parts to simulate ideal switches, care should be taken to ensure that the values for ttran, Rclosed, and Ropenare appropriate for valid simulation results. In this example, we see that the switch and R1 are in series; thus, their resistances add.
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