# Circuit analysis Definition and 218 Discussions

A network, in the context of electrical engineering and electronics, is a collection of interconnected components. Network analysis is the process of finding the voltages across, and the currents through, all network components. There are many techniques for calculating these values. However, for the most part, the techniques assume linear components.
Except where stated, the methods described in this article are applicable only to linear network analysis.

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1. ### Engineering Need help answering questions (Voltage source and 3 Resistors)

Hello. I need help arriving to the answers to the following question above. You will find the circuit attached for Number 1 I though that crrent would be maximum when resistance is replaced with a wire but I couldnt get a an expression for ut. as for question number 2 I tried applying node...
2. ### Engineering How do I find Vth with the node voltage method?

Hello. I'am practicing circuit analisis about the norton and thevenin's circuits and I can't seem to manage to get the right thevenin's voltage using the node voltage for a) resolution 1) I did source transformation turning the current source(2A) into a voltage source (10V) applied node voltage...
3. ### Engineering First Order RL Circuit: Finding a Current I2(0-)

I shorted the inductor and performed mesh analysis. The solutions to the linear system were done using a calculator. The book says that the value for i2(0-) should be 15 mA but I'm getting -2mA. What am I doing wrong? I'm completely confused. Maybe mesh isn't the most efficient way to find I2...
4. ### Engineering Circuit analysis on a supernode

Hello. Can someone give m e pointers on how to find the value of vx given that it is inside a supernode(will it be the valueof the voltage inside or the difference of potential between the two nodes?): here's the exercise and what I've done so far attached. Your time and attention are deeply...
5. ### Engineering Opamp subtractor circuit

So after using superposition and setting the ratio R2/R1 = R4/R3 the same or R2=R4 and R1=R3,i come to the eq. for output voltage Vout= R2/R1 * (V2-V1) or R4/R3(V2-V1). And in the book foundations of analog and digital electronics by agarwal and lang, they are saying that this circuit is a...
6. ### Engineering Opamp adder circuit: Where does the "-" come from?

So i used KCL and both currents are flowing into the node, and then leaving together to go to the resistor R3. So my eq can be seen in the picture. I was looking in a book and they had a minus infront of the parantheses. Is the current flowing from R3 into the node??
7. ### Engineering OPamp circuit - how to simplify this term?

So this is the circuit. And here i tried to calculate Uout/ Uin , any suggestion how to simplify this term?? I used Uout= Uin * (1+ Z2/Z1)
8. ### Engineering Constant current source transistor circuit - differences between 2 types?

So basically we can have a constant current but i dont understand this circuit. for example: i can have the Ia what ever I want with current divider rule: Ia = Iq * R2/R3. So Ia is proportional to the ratio of R2/R3. And if i give a resistor at the collector terminal, if i change it between...
9. ### Engineering Op amp circuit -- Did I calculate the output voltage correctly?

can someone check, if i calculated the output voltage correct? i used virtual ground because V+-input of the op amp is 0 --> V- input is then also 0.
10. ### Simple voltage divider -- why does this work?

Summary:: dont understand how can we use a voltage that has been already dropped. I dont understand the voltage divider. So R1 and R2 are the same. I have 10 V in beginning, then 5V drop across R1 and then i have 5V drop across R2. But how can I use the 5V if they already dropped at R2??? If...
11. ### Engineering Black box which contains 5x 1ohm resistors

You are given a black box with three terminals, as shown below. The box is known to contain five 1-ohm resistors. Using an ohm-meter, you measure the resistance between the terminals to be the following: A - B: 1.5 ohms B - C: 3 ohms A - C: 2.5 ohms Determine the configuration of the five...
12. ### How to use Kirchhoff's voltage law on this circuit?

In this circuit, I have to find the potential at point O. I tried using Kirchhoff's voltage law for the three open loops AOC, AOB and BOC to arrive at potential at O. According to my calculations the potential at O should be 0, but that is not the case according to the source. So I must be using...
13. ### Superposition Principle for two Voltage Sources (confusions about...)

I have a question about natural limitations when the superposition principle for circuits is applicable. Possibly there is a quite elementary reason why the problem I'm going to present next fails, but up to now I haven't a precise reason why that's exactly the case. Could somebody help...
14. ### Find frequency such that two components have same average power

(This is my first time posting here, sorry in advance for any difficulties. ) All componenets of same type has same magnitude, so e.g. the two resistors both have $R$ resistance. Given the difficulty of the previous exercises, I believe I'm over complicating the problem. However, here is what...
15. ### Receiver Circuit Question -- What role does this antenna capacitor play?

Which role plays an additional capacity in a receiver circuit between the antenna and the matching-box part like in this example (found in https://www.frostburg.edu/personal/latta/ee/twinplex/schematic/twinplexschematic.html): Is it neccessary for this receiver circuit or just optional? What...
16. ### Which lamp is dimmed in the circuit?

The true answer is B. But I dont understand why! I know: Kirchhoff's circuit laws : ∑In=0 If we assume that a current that goes from plus to minus, before it passes through lamp B, I know that according to Kirchhof's laws, part of the current will pass through the bottom path where there is no...
17. ### DC current through a resistor circuit

Summary:: Current through a certain resistor in a mixed dc circuit. Hi, Sorry if this is the wrong forum. I'm trying to work out the current through R1.The answer I need is 2 Amp, which I have confirmed with a simulation software. I have calculated the source current as 8A, the current past...
18. ### I Checking for negative feedback in a circuit

This is the circuit in question. During lecture, when checking whether this was negative feedback, my instructor said that if the v_out increases, then v- increases as well, which would lead to the next v_out decreasing because v_out = A(v+ - v-). I get how if v- increases the next v_out would...
19. ### PWM signal generating circuit based on LM393

This is a PWM signal generating circuit based on LM393. When I was running this LM393 circuit, I found that this circuit only consumes about 10 milliwatts of power at a voltage of 5V. Not only that, this circuit can work normally at 3.3V, 12V and 18V. But later I found that this circuit...
20. ### Engineering W0 = 1/RC? Transfer Functions and Bode Plots

Here is the example and solution in full. I have circled where I'm at and highlighted the part that's tripping me up. I managed to get... and getting everything in terms of the angular frequency seems to be critical for getting the plots for the Frequency Response. I checked my notes on RC...
21. ### Engineering Circuit theory: capacitor energy storage and discharging/charging times?

This is not my homework. I took it upon myself to answer a textbook question for mental stimulation. I wanted to know if someone can verify if these were the correct values that needed to be solved for, process, and final answer, and if not, what needed to be considered. For the initial...
22. ### Engineering [Circuit Analysis] Am I on the right track with this problem?

*A is the node all the way to the left above the 30V but I didn’t end up using it because I don’t think you need it since the same as 30V, right? * I know I messed up somewhere because shouldn’t V1-4 = 30? After finding my V1 I used that value to find the other Vs and it ended up being close to...
23. ### Calculating the resistance in a compensating circuit for a thermocouple

Homework Statement:: A K-type thermocouple is connected as shown to sense temperature. The temperature zone is at 25°C. The RTD has a resistance of 100 at 0°C and a TCR coefficient of 0.00385. A 5V power supply drives the circuit. Calculate R2 for proper compensation. What is the emf produced...
24. ### Circuit problem with two sources and three resistors (Nodal Analysis)

Ans: 0.123A Tried mesh analysis and got it but didnt for nodal analysis
25. ### Finding the resonant frequency of this "discriminator" demod circuit.

This is the FM demodulation "discriminator" circuit. It is one of the simplest analog demod setups one could think of. An RF (FM) voltage signal is applied at V12 and the voltage at ' a' ' is supposed to contain the AF signal in its amplitude. The idea behind the circuit is that it resonates at...
26. ### Circuit theory - Resistor function for dynamic non linear circuits

Hi, I'm reading the following paper (L. Chua) about the state-of-art of dynamic non linear circuit analysis -- Chua_Dynamic_Circuits I've a doubt about Theorem 2 on section 3.2 On the Existence of the Resistor Function that establishes sufficient conditions for the existence of network...
27. ### Voltage restriction for nodes on the same branch?

originally ,I wanna prove (TT:current can only flow from c to d),thus I try to figure out what will happen if Vd >Vc,then I label corresponding current direction.Afterwards,I know whats wrong: (A:current doesnt flow out of d ),then I attempted to prove A ,yet I consider that A might not be...

29. ### Checking Kirchhoff's current law

Im trying to apply KCL to the serial c and parallel rl circuit. IZ = = = 330.562 mA but this means incorrect proof. Anyone can help please?
30. ### Electrical How to wire an LED switch based on rated voltage and current

Could someone please help. i need to connect a 12vdc motor which can draw 16 amps to a switch that has an led on it. the led is rated at 3v 20mA. The power supply i am using is rated to put out 12vdc at 30A I thought of the possibility of adding a resistor to the positive pole of the led. In...
31. ### Engineering Understanding the output waveform and using LTSpice

For the following circuit I need to find the output waveform. A. Conceptually I am at sea here but I will have a stab at it. My though process is as follows : At a given instant, the AC voltage is at a fixed value and this value drops (##V_drop##) across the resistor ##R##. The voltage...
32. ### What approach should be used when solving a circuit?

I am close to graduating as an EE major but I have never been able to organize a step by step method on analyzing a circuit. It seems to me that every time I am trying to analize a circuit I end up with a bunch of equations and nothing more. I know that I should: 1. Know what im solving for...
33. ### Physical/conceptual reason for inductor voltage step response

I'm trying to understand the physical reason why when you drive an ideal inductor (no series resistance) with an ideal voltage step input (no series resistance), e.g. some Vin(t) = V0u(t), the output current will be a linear ramp. I can see how to derive this from the inductor equation, v = L...
34. ### Engineering AC transient in an RC circuit

Here, at voltage source zero crossing, cos(2to + pi/4) =0. So, 2to+pi/4 = pi/2 This gives to=pi/8 = 0.3926s. But the given answer is twice the answer I got i.e. 0.7852s. Have I missed anything here?
35. ### KCL got declined in Norton circuit of an ideal amplifier circuit

Hi. Let's say we have a circuit like that, and we want to find the Thevenin/Norton circuit from a and b points. So for Vth, we calculate the Voc, in which we remove the 2K ohm resistor and calculate the Voc. I calculated it correctly. But I have problem in calculating the Norton current. So in...
36. ### Engineering Help finding this node voltage

I am given that all the BJTs are the same. First of all, when finding node voltages like Vref should I make the node voltage a voltage source first and then do circuit analysis? If so then I would use KVL but that does not give me Vref = 2Vbe. I do know that Vref = Vb1 = Vb2. What am I doing...
37. ### Kirchoff's laws and capacitance

Equivalent capacitance before and after remains the same. Now the 10F capacitor (which was initially connected in parallel with 20F) would have 30 C charge. Hence an additional 20C must have been supplied to it. The only path which may supply the charge is through battery. However this leads...
38. ### Heat dissipated in a Resistor-Capacitor circuit

I tried to conserve the charge on the left plates of both the capacitors as intially the total charge on both is 48 and at t=t0 the total charge is 36(on c1) +4V(V is the potential across c2) so i got V=3 and then i conserved the energy Initial energy on both capacitor = final energy on both +...
39. ### Finding the fault in this circuit (UV lamp controller)

Guys this circuit and shematic is of UV lamp controller.. It burns sometime as shown in figure can someone tell the reason?
40. ### R_th wrong while applying series and parallel simple theory

Summary:: Trying to find Rth but I do not get the same value as the one from the solution. [moderator: moved from a technical forum. No template.] I am trying to find Rth to solve this problem, however once I simplified it, I get a value of 700.745 Ω while in the solution, the answer is...
41. ### Guitar effect soundwave

I built a guitar (fuzz) effect, and analysed the sine wave from a tone generator through an oscilloscope. Wondering what the wave means and how it got to be the way it is. I will attach a picture of the oscilloscope screen + the circuit I used for the Fuzz effect. My question is what the cause...
42. ### Engineering Find the output resistance in a amplifier (MOSFET) small-signal model

I have to solve a problem related with an 'invented' (non-real) MOSFET working in its saturation region (amplifier). I have solved all the questions, but I'm unable to get the last one. Basically, I need to determine the output resistance of the amplifier as a function of other given 4...
43. ### What is the total voltage?

I really don't have any clue why the total voltage is equal to the voltage drop over the 3 Ω and 2 Ω resistors and independent of the 4 Ω resistor . Does it have to do with parallel circuits?
44. ### A circuit with switches, capacitators and resistors

To solve this question first I calculated the potential energy the capacitor A stored. It's equal a: Ca.V²/2. Ok, so when switch S1 is open and S2 is closed I calculated the equivalent capacitance as if they were in series --> 1/Ceq = 1/Ca + 1/Cb --> Ceq = (Ca.Cb)/(Ca+Cb). So I used the formula...
45. ### Engineering A circuit with non-linear devices

I honestly don't know how to quite even begin this problem. Looking at Fig 3-2, the slopes of the graphs are 1/R, and hence where the slopes are 0, we have infinite resistance, in which case current wouldn't flow through that resistor and hence simplify the circuit. So I was trying to find...
46. ### Engineering Finding voltages in a linear circuit

From the circuit I have: ##-v_b + v_a + V = 0## ##v_b - V = v_a## ##i_1 = (v_b - V)/R_1## ##I + i_2 = i_1## ##(v_b - V)/R_1 = I + v_b/R_2## From this last equation I get ##v_b = 10.8## and hence ##v_a = 5.8##. However, apparently that is wrong. (And hence my answers to #2 were all wrong as...
47. ### Finding the missing current and voltage in a circuit with superposition

I don't get this. Since we have analyzed the circuit separately for each source, adding them should give me the final values of I1, V2, I2, V1 etc. However, that's not quite true—from cases 1 and 2, I should have I1 = 4 + 5 = 9 mA, but it's 8mA. Hence, I thought that the black box consumes 1mA...
48. ### Engineering Finding the Thevenin equivalent Resistance for circuit with voltage dependent sources

I am having a hard time solving this. Letting \$i\$ be the current flowing into ##R_3##, ##i_1## the current flowing through ##R_1## and ##i_2## the current through ##R_1##—and the node between R3 and R1 be e_1; Using KVL and KCL, I've managed to find that ##i + I = i_1 + i_2## Hence...

thanks
50. ### Introductory Circuit Analysis—power ratings

I am going through "Circuit Analysis for Dummies". On pg 18, it says, "If you calculate the power dissipated as 0.1 watts, then a 0.25-watt resistor can handle this amount of power. A 0.125-watt resistor should be able to handle that amount as well, but when it comes to power ratings, err on the...