Thevenin equivalent circuit

An equivalent Thevenin circuit is shown in Fig. 6.72. If VL is the potential difference across the impedance of the load 2EL (e.g. the recorder in the above example), then ... 

Fig. 15 Crosstalk noise due to parasitic of the switch and its Thevenin s equivalent circuit...

Then applying Thevenin s " theorem, the equivalent circuit can be represented as show n in Figure 18.18(b). On application of a voltage surge, the arrester will start... 

Figure 18.18 Equivalent circuit applying Thevenin s theorem...

According to this model, the SEI is made of ordered or disordered crystals that are thermodynamically stable with respect to lithium. The grain boundaries (parallel to the current lines) of these crystals make a significant contribution to the conduction of ions in the SEI [1, 2], It was suggested that the equivalent circuit for the SEI consists of three parallel RC circuits in series combination (Fig. 12). Later, Thevenin and Muller [29] suggested several modifications to the SEI model ... 

The diode voltage is 0.75251 V, and the diode current is 4.248 mA. The diode voltage and current of this circuit are the same as the diode voltage and current of the previous example. This result should be expected since the Thevenin equivalent of V1, Rl, R2, and R3 in this exercise is exactly the same as the circuit of die previous example. ... 

Capture and PSpice can be used to easily calculate the Norton and Thevenin equivalents of a circuit. The method we will use is the same as if we were going to find the equivalent circuits in the lab. We will make two measurements, the open circuit voltage and the short circuit current. The Thevenin resistance is then the open circuit voltage divided by the short circuit current. This will require us to create two circuits, one to find the open circuit voltage, and the second to find the short circuit current. In this example, we will find the Norton and Thevenin equivalent circuits for a DC circuit. This same procedure can be used to find the equivalent circuits of an AC circuit (a circuit with capacitors or inductors). However, instead of finding the open circuit voltage and short circuit current using the DC Nodal Analysis, we would need to use the AC analysis. 

For this example, we will find the Thevenin and Norton equivalent circuits for the circuit attached to the diode in EXERCI5E 3-5. The circuit is repeated below ... 

This circuit is difficult because it contains a nonlinear element (the diode) and a complex linear circuit. If we could replace VI, Rl, R2, and R3 by a simpler circuit, the analysis of the nonlinear element would be much easier. To simplify the analysis of the diode, we will find the Thevenin and Norton equivalent circuits of the circuit connected to the diode that is, we will find the Thevenin and Norton equivalents of the circuit below ... 

We will convert this circuit into the Thevenin equivalent ... 

For determining the diode voltage and current, this circuit is much easier to work with than the original. This example is concerned with finding the numerical values of the equivalent circuit. The analysis of the circuit above was covered in Section 3.C. We will now find the Thevenin and Norton equivalent circuits of the circuit shown below ... 

EXEHCI5E 3-B Find the Thevenin and Norton equivalent circuits for the circuit below ... 

Other methods to simplify the circuit are Thevenin s and Norton s theorems. These two theorems can be used to replace the entire circuit by employing equivalent circuits. For example, Figure 2.34 shows a circuit separated into two parts. Circuit A is linear. Circuit B contains non-linear elements. The essence of Thevenin s and Norton s theorems is that no dependent source in circuit A can be controlled by a voltage or current associated with an element in circuit B, and vice versa. 

Thevenin s theorem states that a section of a linear circuit containing one or more sources and impedances can be replaced with an equivalent circuit model containing only one voltage source and one series-connected impedance, as shown in Figure 2.35. 

To determine the Norton equivalent impedance ZG in Figure 2.36, we can kill all the sources in circuit A and then calculate the impedance from n-n terminals by looking back into circuit A. Thus, the Norton impedance ZG is equal to the Thevenin impedance. The Norton current IQ is a constant current that remains the same regardless of the impedance of circuit B. It can be determined by... 

Note that only at the output terminals n-n are the Thevenin and Norton equivalents the same. In other words, at the output terminals n-n the voltage and current of the Thevenin equivalent circuit and the Norton equivalent circuit are identical. 

The equivalent circuit fed from a Thevenin voltage source is shown in Fignre 15.11. 

However, this may not be quite the case (another case of bad notation). In fact, the author suggests a relaxed condition for an MSA, namely one that scatters (in total) only as much as it absorbs—that is, one that is constrained only by condition 1 above (most antennas scatter more in total than they absorb, never less). As we shall see, this relaxed condition leads to a much broader class of antennas, some of which are truly noteworthy. The three examples presented above are excellent illustrations of these concepts. However, let us briefly remind the reader about the Thevenin equivalent circuit as it applies to receiving antennas. 

It is well known that any receiving antenna can be described by a Thevenin equivalent circuit, shown in Fig. 2.13. Here the power delivered to the load impedance Zl will always correctly represent the power being absorbed by the antenna, while the power being lost in represents power being reradiated somewhere in space by the antenna. However, the antenna may actually scatter considerably more power than is being lost in Za-... 

Fig. 2.13 The Thevenin equivalent circuit for a receiving antenna always yields the correct power delivered to the load impedance Zl. The power lost in the antenna impedance Za represents power scattered somewhere, not necessarily in the back direction. Additional scattering not accounted for by Za will in general take place.

Thus, this antenna is truly an MSA in the rigorous classical sense. In addition, the Thevenin equivalent circuit will correctly describe all of these features as far as the array in Example I is concerned. 

It was further demonstrated that if we relaxed the conditions above to merely the first, namely that the antenna should scatter no more total energy than it absorbs, it could lead to antennas with virtually no residual scattering (but not necessarily so). An interesting feature of this class of antenna is that the Thevenin equivalent circuit may no longer correctly predict that the total scattered power as merely associated with under all load conditions. This should be accepted as a fact of Ufe, and failing to realize this can lead to fatal mistakes. 

The second scheme is shown in Fig. D.13. Here aU elements are loaded directly with the same load impedances Zi and exposed to an incident plane wave (note no connectors are necessary, strictly speaking). From the Thevenin equivalent circuit shown in the insert we then have... 

Eq. (10) indicates that the sources in the heart can be replaced by an equivalent double layer on the surface of the heart. From a theorem of Helmholtz, this double layer should be o times the voltage which would appear on the surface of the heart when it is insulated (Helmholtz, 1853) (Thevenin s theorem in circuit theory is a special case of Helmholtz theorem.) From Eq. (6) it is evident that Eq. (10) is consistent with Helmholtz theorem. 

The modeling of an accumulator or battery of accumulators is a highly complex task. There are many different approaches, which will be more or less appropriate depending on the objectives reqnired of the model. In order to replicate electrical behavior similar to that of a battery, we nse a model in the form of an equivalent electrical circuit. Many different circuits are put forward in the existing body of literature Thevenin equivalent circnit, improved Thevenin equivalent circuit, FreedomCar, etc. In all cases, the parameters nsed for these models are determined experimentally. 

Calculate the potential-drop on a given resistivity in an arbitrary DC circuit. Prove that this task could be solved by the minimization of the sum of dissipation potentials or by the principle of minimal entropy production, like we did in the serial connection of the Figure 5., when the circuit regarding the contacts of the resistor is replaced with the Thevenin s potential source equivalent circuit p],... 

The Thevenin equivalent circuit is the simplest combination, since it is the association of an ideal voltage source and a resistor connected in series. This is a much more realistic way of modeling a lead-acid battery. Indeed, the resistor illustrates the voltage drop due to the current passing through the components of the battery. In the case of LABs, this instantaneous voltage drop mainly results from the low electrical conductivity of electrolyte and is proportional to the current. But, such a simple combination does not account for the polarization of the electrodes happening later on, when the battery is operated. 

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