1. ### 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...
2. ### 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...
3. ### 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...
4. ### 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...
5. ### 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?
6. ### 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...
7. ### 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...
8. ### 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...
9. ### 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 +...
10. ### 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?
11. ### 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...
12. ### 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...
13. ### 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...
14. ### 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?
15. ### 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...
16. ### 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...
17. ### 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...
18. ### 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...
19. ### 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
21. ### 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...
22. ### Engineering AC circuit: Find the current through the inductor & capacitor

Hi! I wonder if it is correct. Can someone confirm (maybe with a software) ? I(L) = I2 I(C) = I2 - I3 -- Thanks.
23. ### Engineering Homework: Rx=? to get maximum power transfer at point M

Hi, after calculations I end up in the circuit below¨ (Thevenin equivalent) So now I have to say Rth=RL and I will find Rx ? The initial circuit is this: Thanks
24. ### Engineering I can't determine the capacitive and inductive resistance of the circuit

Hi, I'm trying to solve this but it becomes difficult. I'm using KCL and I repalce ZL = j0,1ω (Ω) , ZC=... etc. Finding 3 equations with 3 unknown variables (plus the ω). And now is the time for Cramer's rule. I'm not sure if I should move on. What do you say ? I'm on track ? Thanks. ..
25. ### Engineering Dependent source problem using KVL

Hi all, I was trying to solve this but I'm stuck as you can see in my notes below: Using simulator the I1=3.125 A | I2=-1,857 A | I3=4,375 A and Power of the dependent current source = -46.875 W Any idea, what could be wrong ? Thanks.
26. ### Engineering Measuring the damping frequency from an oscilloscope reading

I know the following equations for if the damping ratio is less than 1: $$\sigma = -\zeta \omega_n$$ $$\omega = \sqrt{(1 - \zeta ^2)\omega^2_n}$$ I am given the following circuit that I built on LTSpice: Measuring the voltage between node 2 and ground (blue), and the voltage Vc4(t) (green) I...
27. ### Engineering Determine if the dependent source of the circuit delivering power or...

Hi all ! I want a confirmation for this exercise please. The circuit: This is my try: https://www.docdroid.net/EFuTDMp/new-doc-2019-10-03-234340-1-converted.pdf -- Thanks
28. ### Help with Circuit Nodal Analysis

Summary: Perform nodal analysis on a circuit to find voltages. For a laboratory I am trying to find the nodal voltages for a circuit we built using hand calculations. I have the answer as we ran the simulation which shows all the nodal voltages, however my nodal analysis seems to be wrong as I...
29. ### Engineering Transient circuit analysis problem with a dependent source

Hi all, I tried to solve this, but I can't find the R(equal). I use the following method. The circuit: For t<0 the switch is closed so the iL(0-)=4 A For t>0 it opens and the iL(∞)=0 A Now, I want to find the value τ=L/R(equal) Then I will use the: iL(t) = iL(∞) + ( iL(0-) - iL(∞) )* (...
30. ### Find the Vo of the AC circuit

This is the circuit: I try with KVL: But the given answer is 6.66L33.67 Volts. So, I'm confused, any suggestions ?