# What is Thevenin equivalent: Definition and 160 Discussions

As originally stated in terms of direct-current resistive circuits only, Thévenin's theorem states that, "For any linear electrical network containing only voltage sources, current sources and resistances can be replaced at terminals A-B by an equivalent combination of a voltage source Vth in a series connection with a resistance Rth."

The equivalent voltage Vth is the voltage obtained at terminals A-B of the network with terminals A-B open circuited.
The equivalent resistance Rth is the resistance that the circuit between terminals A and B would have if all ideal voltage sources in the circuit were replaced by a short circuit and all ideal current sources were replaced by an open circuit.
If terminals A and B are connected to one another, the current flowing from A to B will be Vth/Rth. This means that Rth could alternatively be calculated as Vth divided by the short-circuit current between A and B when they are connected together.In circuit theory terms, the theorem allows any one-port network to be reduced to a single voltage source and a single impedance.
The theorem also applies to frequency domain AC circuits consisting of reactive and resistive impedances. It means the theorem applies for AC in an exactly same way to DC except that resistances are generalized to impedances.
The theorem was independently derived in 1853 by the German scientist Hermann von Helmholtz and in 1883 by Léon Charles Thévenin (1857–1926), an electrical engineer with France's national Postes et Télégraphes telecommunications organization.Thévenin's theorem and its dual, Norton's theorem, are widely used to make circuit analysis simpler and to study a circuit's initial-condition and steady-state response. Thévenin's theorem can be used to convert any circuit's sources and impedances to a Thévenin equivalent; use of the theorem may in some cases be more convenient than use of Kirchhoff's circuit laws.

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1. ### Determine Thevenin equivalent circuit.

Here is the circuit that we need to find the Thevenin equivalent of I am really not confident that the attempted solution below is correct. Let's put a test current source between the terminals we're interested in First let's compute the open circuit voltage. We set the newly introduced test...
2. ### Differential Amplifier Common Mode Thevenin Equivalent

I am currently reading about small signal analysis of a MOSFET differential amplifier. The text I am using has the below two figures for a common-mode equivalent circuit for the amplifier. The first makes sense to me except where it calls it a "Norton equivalent circuit", whereas I thought a...
3. ### Engineering How to Calculate Thevenin Equivalent Circuit

First, I calculate the Thevenin resistance by treating the independent current source I0 as an open circuit and noticing that the resistance of the dependent voltage source is α (since V=IR and the voltage across the dependent voltage source is given by αi. In this way, I have: RTH = 1 / (1 /...
4. ### Engineering Problem with the Thevenin equivalent resistance

Good day I have a problem to find the equivalent resistance from the capacitor point of view the solution says it's R1 but for me we still have R2 and R3 we have not deal with ! many thanks in advance

6. ### Finding the Thevenin equivalent by zeroing

I am asked to find the Thevenin equivalent for the circuit above. I already got the equivalent voltage by node analysis on the nodes B and A3. What I'm trying to do is to zero the 10V-source and then calculate the equivalent resistance between A3 and GND. Whatever expression I come up with...
7. ### Thevenin equivalent by source transformation

Homework Statement Find the Thevenin equivalent at terminals a-b V1 = 70V V2 (dependent) = 4Vo R1 = 10Kohm R2 = 20Kohm Homework Equations ##V=RI## ##1/req = 1/r1 + 1/r2 + ... +1/rn## The Attempt at a Solution Found the current i = 1mA by KVL using Vo = 10ki then did source...
8. ### Thevenin Equivalent : Wrong value for Rth

Homework Statement The problem ask for Thevenin Equivalent for the circuit attached. Homework Equations Vth = Vab Rth = Req Rth = Vth / Isc Rth = 1 / It The Attempt at a Solution Already calculated Vth = 166.67 V. I've no problem with that. Already confirmed by textbook answer. However, my...
9. ### Thevenin equivalent (symbolic circuit calculation)

Homework Statement I have trouble to find the right procedure to transform the circuit below to a thevenin equivalent. I am looking for a symbolic solution a step by step guidance of where to start and how to add/locate all the impedance in series and parallel in order to calculate the sum of Z...
10. ### Engineering Finding the Thevenin Equivalent Circuit for a Network with a Load Resistor

Homework Statement I just want to check to see if my understanding in anything here has gaps. Q: Find the Thevenin equivalent circuit for the network external to he load resistor ##R_L##: Homework Equations Ohm's Law: ## V = IR ## Kirchoff's Voltage Law: Σ##V_{drops}## + Σ##V_{gains}## = 0...
11. ### Engineering Find the Thevenin equivalent circuit

Homework Statement Find the Thevenin equivalent circuit for the portions of the networks in the following circuit: Homework Equations Kirchoff's Voltage Law: ΣVdrops = ΣVgains Kirchoff's Current Law: ΣIclosed loop = 0 Ohms Law: V = IR The Attempt at a Solution Determination of the Thevenin...
12. ### I finding the Thevenin equivalent resistance

Homework Statement https://imgur.com/a/XD3Km4t I'm trying to find the thevenin equivalent resistance across the opened terminals. Homework Equations I know you short circuit the voltage source and do simple circuit analysis, however I'm getting confused in determining what resistors are...
13. ### Engineering Attempt at Thevenin Equivalent Circuit

Hi, I am having trouble trying to determine Voc on this circuit. I have done the following to attempt it: 1) Converted my Voltage source to rectangular format (from polar) 2) Converted my capacitor and inductor to Xc and XL 3) I tried using KCL to find Va that's at the three-way on the circuit...
14. ### Engineering Find the Thevenin Equivalent circuit

Find Thevenins Equivalent circuit external to RL, then find I. Here's my work : 5Ω & 5Ω series → R(1) = 5+5 = 10 Ω 10Ω & R(1) parallel→ R(2) = (10*10)/(10+10) = 5 Ω 2Ω & R(2) series → R(3) = R Th = 5+2 = 7Ω V = I R R = (R Th * RL)/(R Th + RL) R = 70/17 Ω V = 5 * (70/17) = 350 / 17 V = 20.6...
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### Why do I get different answers with different methods - Thevenin

Homework Statement Determine the Thevenin equivalent of the following circuit: https://imgur.com/a/74UjA (Top image) Homework Equations - The Attempt at a Solution The last 3 images in the Imgur album are all different approaches. I can't figure out what the right one is, and why the other...
16. ### How Do Controlled Sources Impact Thevenin Equivalent Calculations?

Homework Statement [/B] Homework EquationsThe Attempt at a Solution First I found the equivalent resistance since the 3 ohm resistor and 6 ohm resistor are in series. 9ohm. Then I did chose the node where the arrow points to as Voc, which is also va. KVL: (va+24V)/9ohm=1.33va I get va to be...
17. ### How to know when to use Voc/Isc or Vtest/Itest for Thevenin?

should you only apply the test sources when there are only independant sources in the circuit. Also would it be valid to zero all dependant source so that you are only left with independant sources and then apply the test source. It seems like i am always applying open and short circuit...
18. ### Current through an Ammeter in an Electric Circuit

Homework Statement [/B] It is required to find the current through the ammeter, marked A, in the above figure.Homework Equations ##V=iR##The Attempt at a Solution I've redrawn the circuit as follows - But don't know how to obtain the value ##i_3##
19. ### Engineering Open-circuit voltage in Thévenin equivalent

Homework Statement Determine the Thévenin equivalent of the following circuit with respect to terminals A-B Homework Equations $$U=RI$$ The sum of the currents in a node is zero. The sum of voltages in a mesh is zero. I'm always considering the currents in the resistors directed downwards...
20. ### Computation of Thevenin Equivalent

Hello! Recently I was going through some old exams and upon encountering this problem (which seemed pretty easy) I got stuck. Exams at my university are composed of individual tasks, each having three subquestions with four plausible answers respectively. Solution sheet gives results only, so...
21. ### Thevenin equivalent diamonda shaped

【Mod Note: thread moved from technical forum, so homework template is missing】 Hi every one! I am encountering difficulties on finding the Req. in the sense that i can't really see which is in parallel end which is not, especially on the diamond shape. I haven't really understood how to treat...
22. ### Engineering Converting to a circuit's Thevenin equivalent?

Homework Statement Homework Equations Finding the Thevenin equivalent? The Attempt at a Solution I found the thevenin resistance to be 185/47 ohms, which came out to be correct. I've been struggling with this question all day. I ended up attempting to find the norton equivalent and then...
23. ### Engineering Understanding thevenin's circuit in linear circuits

Homework Statement This is one of the problem i had had some help in solving but some things remain unclear to me and i will highlight them by posting the exact question in the brackets next to the line of solution so that you can see what bothers me. Hopefully you can help me better understand...
24. ### Engineering Finding Thevenin Equivalent Circuit for a Complex Network

Homework Statement Homework Equations Thevenin Equivalents V = IR The Attempt at a Solution To try to find R_th, I replaced all the voltages with short circuits but I do not what to do next. Then I believe V_th would just be the same as the voltage of the rightmost resistor.
25. ### Engineering Finding Thevenin Equivalent Voltage for a Circuit with Multiple Voltage Sources

Homework Statement See attached image Homework Equations Thevenin EquivalentThe Attempt at a Solution a) Find the total resistance between A and B by short circuiting the voltage sources: Rt = 100Ω in parallel with the two 150Ω Two 150Ω in series: R = 300Ω 1/Rt = 1/100 + 1/300 Rt = 75Ω I...
26. ### Thevenin reduction of network for fault analysis trouble.

Homework Statement Reduction from top network to bottom network in the screen shot. I can not find the steps that have been taken to do this. Fault impedance = Zfa = Zfb = Zfc = j0.5 Homework EquationsThe Attempt at a Solution in hand written screenshot, sorry for the mess, just to show it...
27. ### Fault analysis -- Simplifying to Thevenin equivalent

Homework Statement [/B] All voltages and impedances are in per unit values. After all the source transformations, why is the voltage source still 1 ? Homework EquationsThe Attempt at a Solution [/B]
28. ### Find Thevenin Equivalent of Circuit

Homework Statement Find the Thorton equivalent of the circuit shown [/B] Homework Equations Voc=IscRs Rseries=R1 +R2+... Rparallel=R1-1+R2-1+... The Attempt at a Solution So, I thought I should first solve for the Rsource, by shorting all of the voltage sources: However, I don't think the...
29. ### Rth = (8 || 12) + 36 = 74.2 Ohms

Homework Statement Find the thevenin equivalent of the cicuit shown below with V=500 V and i=10 A Homework Equations Voc=Vth Isc=VN The Attempt at a Solution [/B] So, to solve this, I used my instructors method of first finding the Rth. So, what I did was set the independent sources to...
30. ### Find thevenin equivalent resistance with diode.

Homework Statement I have a circuit with a diode in it. I have to find the thevenin equivalent in order to reduce the circuit to a DC source, single resistor and single diode. How do I account for a diode when trying to find Rth and Vth? Do I just remove it and have it act as a short circuit or...
31. ### Engineering Find the Thevenin Equivalent Circuit

Homework Statement Homework Equations Node Voltage Method V=IR The Attempt at a Solution KCL at Node 1: KCL at Node 2: i is the current moving towards "a" I've simplified the two equations down but the problem I run into is that normally I'm able to write a third equation to define i0...
32. ### Thevenin Equivalent & Available Power?

Homework Statement Homework Equations V=IR Node Voltage Thev/Nort The Attempt at a Solution So I set up my equations in the picture below, but I'm kinda confused about the Vx's in the equations. First, did I set these up correctly? If so, solving them I get that V2=0 which would mean my...
33. ### Engineering Thevenin Equivalent of AC RLC Circuit w/ Dependent Voltage

Homework Statement Find Vth and Zth. frequency = 2kHz Homework Equations w = 2 * (pi) * f ZL = j w L ZC = -j / (w * C) V = I*Z ZR = R The Attempt at a Solution At first I tried using nodal analysis which I receive the value V = 0 v. I believe this is because this circuit only has dependent...
34. ### Engineering How do I find the Thevenin Equivalent of this circuit?

Homework Statement I need to find the Thevenin Resistance and the Thevenin Voltage Homework Equations Vth =Rth I (Short Circuit) The Attempt at a Solution I know the answer is supposed to be Rth = 3Ω and Vth = 0.5V, but I couldn't get there with my method. I only get the Rth to be 3 Ω if I...
35. ### Determining Thevenin equivalent and time constant

Homework Statement Homework Equations ; 3. The Attempt at a Solution [/B] Here is my thought process and assumptions. Without Vs1 and R2, the open-circuit current would be Vs2/R2, but I know Vs1 and R1 must be contributing in some way. I'm thinking of summing the Voltage sources and using...
36. ### Engineering What are the implications of Thevenin equivalent circuits on circuit behavior?

Hiya, this is my first time posting so apologies for any errors in formatting. :oldsmile: I am confused as to whether when Thevenising a portion of a circuit is it to simplify BUT provide the same output characteristics, meaning the workings of the Thevenin part of the circuit may behave...
37. ### Thevenin equivalent resistance problem

Homework Statement Homework Equations V=IR The Attempt at a Solution [/B] I found that the current around the circuit was 5mA using kirchhoffs law ( i think) If this is true then the T.E.V should be the voltage across the 120ohm resistor which is .6V (120*5e-3). Now I'm stuck and not sure...
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### Thevenin's circuit analysis. Multiple voltage sources

Hi, i am halfway through one of my assignments and i require some assistance. I do not seek the answer to the assignment just a little boost to my knowledge. 1. Homework Statement Basically, if i am calculating the Thevenin's voltage and the resistor i have removed that is in question has a...
39. ### Finding Thevenin Equivalent with Dependent Source

Homework Statement I am trying to find the Thevenin Equivalent of this circuit Homework Equations Using KCL and node voltage The Attempt at a Solution I found the open circuit voltage for the thevenin voltage so far by the mesh current method, and now I am trying to find the closed circuit...
40. ### Thevenin Equiv with just Capacitors

Homework Statement imgur link: http://i.imgur.com/TWB5rRu.png Homework EquationsThe Attempt at a Solution I can find the equivalent capacitance, 10F, but I'm not really sure how to find the equiv. Thev. voltage. I figured that with the voltage source present, half the voltage will be lost...
41. ### Thevenin Equiv.: Solving Homework Equation V=IR

Homework Statement Homework Equations V=IR The Attempt at a Solution I am not sure if I did this problem correctly. To find the thevenin equivalent do you have to get the circuit into series first? I combined the resistors in parallel and found the Vth to be 6V and Rth to be 8ohms. Is...
42. ### Engineering How Do You Calculate Thevenin Voltage Using Superposition?

Homework Statement http://puu.sh/lQPvh/d0efa216ff.png Homework EquationsThe Attempt at a Solution http://puu.sh/lQPAR/2456db4783.jpg http://puu.sh/lQPCJ/f142c25f63.jpg http://puu.sh/lQPER/5eb4af107e.jpg Is this correct? I used principle of superposition to calculate the Thevenin...
43. ### Calculating Thevenin Equivalent Doesn't Seem Practical

Ok, so I know the point of the Thevenin is to make a simpler circuit so that that it results in the same current being sent to the other connected circuit. But why do we go through all the hassle of computing the Thevenin Voltage when we could choose any arbitary Voltage and a Resistor that...
44. ### Engineering How Do You Determine Thevenin Equivalent Circuits and Maximize Power Transfer?

Homework Statement Find the Thevenin equivalent circuit for the circuit shown. You will need to find VOC and then use the test source method to find the Thevenin resistance. Using the Thevenin equivalent circuit,determine the load resistor that results in maximum power transferred to that load...
45. ### Thevenin equivalent sc current

Homework Statement [/B]Homework Equations [/B] Node-voltage method mesh current methodThe Attempt at a Solution [/B] My problem is with the short-circuit current. There are three meshes when you join the nodes a and b. Let i1 be the cw current for the bottom right mesh, i2 be the ccw...
46. ### Thevenin Equivalent Finding Isc

Homework Statement Homework EquationsThe Attempt at a Solution So far I've found Vout, but I'm a little confused about finding ISC. The solution to my homework says that in Figure 2 the 10 ohm resistor gets by passed due to the short across the open voltage. Why does this happen? Thanks!
47. ### Determining Thevenin equivalent resistance

I am currently learning about Thevenin equivalent circuits and was posed with the question attached to this post. I was wondering why I3 is equivalent to the current formed by a short circuit between nodes a and b. Shouldn't the current between a and b be I1 + I2 + I3 since in a short circuit...
48. ### Find V0, ISC, & RTH: Thevenin Equivalent Homework Soln

Homework Statement Find the open circuit voltage V0, short circuit current ISC, and RTH, Homework EquationsThe Attempt at a Solution I found the equivalent resistance to be 20 ohms(just by combining resistors in parallel and series) and V0 to be 30V, which I think might be wrong. I did a...
49. ### Engineering Exercise about Thevenin equivalent circuit

Hi all :) I'm trying to figure out the Thevenin equivalent of this circuit: I start by switching off every source and calculating the equivalent resistance: RTh = RN = (6 + 14) || 5 = 4 Ω Then I proceed with finding the voltage at 2. I note that the nodes between 1 and 2 form a...
50. ### Finding Thevenin Voltage in a Complex Circuit

Homework Statement The question is in the photo attached. Homework EquationsThe Attempt at a Solution I have found the Thevenin voltage as the 10 and 20 ohm resistors are in series (30 ohms) and the 50 and 40 ohm resistor are in series (90ohms). The 30 and 90 ohm resistors are in parallel so...