Node voltage analysis

The node voltage analysis performed by PSpice is for DC node voltages only. This analysis solves for the DC voltage at each node of the circuit. If any AC or transient sources are present in the circuit, those sources are set to zero. Only sources with an attribute of the form DC=l/ff/i/ff are used in the analysis. If you wish to find AC node voltages, you will need to run the AC Sweep described in Part 5. The node voltage analysis assumes that all capacitors are open circuits and that all inductors are short circuits. 

To illustrate an example with dependent sources, we will perform a node voltage analysis on the circuit below. If you are unfamiliar with wiring a circuit, review Part 1. Create the circuit below. 

It is assumed that the student has been given enough information to completely analyze the circuit. This manual assumes that the student wishes to check his or her answers (or intuition) with this program. The student would construct the circuit as shown in Part l and then run either the node voltage analysis in Part 3 or the DC Sweep in Part 4. This circuit is different from the circuits in Parts 3 and 4, but the procedure given in those parts can be applied to the circuit. 

We will run the analysis to calculate all node voltages and all branch currents. Select PSpice and then Run from the Capture menus ... 

This is an iterative technique used to solve linear electric networks of the ladder type. Since most radial distribution systems can be represented as ladder circuits, this method is effective in voltage analysis. An example of a distribution feeder and its equivalent ladder representation are shown in Fig. 10.116(a) and Fig. 10.116(b), respectively. It should be mentioned that Fig. 10.116(b) is a linear circuit since the loads are modeled as constant admittances. In such a linear circuit, the analysis starts with an initial guess of the voltage at node n. The current I is calculated as... 

Thermal analysis is really no more diffieult than Ohm s Taw. There are similar parameters to voltage, resistanee, nodes, and branehes. For the majority of elee-tronie applieations, the thermal eireuit models are quite elementary and if enough is known of the thermal system, values ean be ealeulated in a matter of minutes. If one has a temperature-measuring probe, the thermal eomponents ean also easily be measured and ealeulated. 

Electronics has, in fact, been a very fertile area for SEM application. The energy distribution of the SEs produced by a material in the SEM has been shown to shift linearly with the local potential of the surface. This phenomenon allows the SEM to be used in a noncontact way to measure voltages on the surfaces of semiconductor devices. This is accomplished using energy analysis of the SEs and by direedy measuring these energy shifts. The measurements can be made very rapidly so that circuit waveforms at panicular internal circuit nodes can be determined accurately. 

The DC Nodal Analysis finds the DC voltage at every node in the circuit. The voltages are relative to ground. 

Notice that we have added a bubble at the voltage reference node so that we can easily plot the voltage. The name for this part in Capture is Vcc. Select Place and then Power from the menus to place it. We will run the same temperature analysis as... 

The DC Sweep can be used to find DC voltages and currents for multiple values of DC sources. It can answer the following question in one simulation What is the voltage at node 1 for VI = 10 VDC, VI = 11 VDC, and VI = 12 VDC This question could be answered using the DC Nodal Analysis if the DC Nodal Analysis were run three times. 

The center frequency is 1 kHz, This frequency was chosen to match the frequency of the sinusoidal input voltage. The harmonics that will be calculated are the first nine 1 kHz, 2 kHz, 3 kHz, 4 kHz, 5 kHz, 6 kHz, 7 kHz, 8 kHz, and 9 kHz. There may be others, but we want numerical values for only the first nine. The output variable for the Fourier analysis is the voltage at node Out, VfOUt). This is the output of the amplifier. We could look at the frequency components of any voltage or current, but for this example we are interested only in the output. Click the OK button twice to accept the settings and then run PSpice. 

The analysis is set to WOCSt-Case/SenSltlVlty. The Output Variable is VfVOj because we are interested in the maximum voltage at this node. Click the More Settings button ... 

In nodal analysis, the voltages between adjacent nodes of the network are chosen as the unknowns. This can commonly be achieved by selecting a reference node from the graph of the network. Equations are then formed if KCL is employed. By equating the sum of the currents flowing through admittances associated with one node to the sum of the currents flowing out of the current sources associated with the same node, a set of equations can be established with the form of [F][V] = [/] ... 

If we do a similar analysis for the turn-off transition (right side of Figure 5-5), we will see that for the switch current to start decreasing by even a small amount, the diode must first be positioned to take up any current coming its way. So the voltage at the switching node... 

The spectral analysis of fluctuations yields also valuable information, and it can be used to test the validity of kinetic schemes describing the transitions between different channel states. In Ranvier nodes the component of the sodium current fluctuations which corresponds to the sodium inactivation process observed in voltage-clamp experiments is much larger than expected from a simple Hodgkin-Huxley scheme with statistically independent activation and inactivation processes. This finding provides a strong argument in favour of the hypothesis that the inactivation process is at least partially sequential to the activation process. 

In the EMTP, the nodal analysis method is adopted to calculate voltages and currents in a circuit. Figure 1.68 shows an example. By applying Kirchhoff s current law to nodes 1-3 in the circuit ... 

It is clear from Equation 1.265 that once the node conductance matrix is composed, the solution of the voltages is obtained by taking the inverse of the matrix, as the current vector (J) is known. In the nodal analysis method, the composition of the nodal conductance is rather straightforward, as is well known in circuit theory. In general, nodal analysis gives a complex admittance matrix because of jcoL and jcoC. 

Those analogies are not perfect for two related reasons. (1) In electrical circuits, we (generally) deal with the voltage at two points on each discrete component - the nodes of the circuit - while for thermal problems we often need to consider the temperature throughout the volume - as a function of x, y, and z. (2) In electrical circuits, the significant resistance and capacitance are usually easily separable - a resistor has negligible capacitance, and a capacitor has negligible resistance. In thermal circuits, that is not often the case - thermal circuits often have chunks of material whose thermal impedance and heat capacity are not separable. These differences make the transient analysis of thermal circuits more difficult than for electrical circuits. Such problems are expressed and solved as differential equations. 

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