Questions tagged [circuit-analysis]

Circuit (Network) analysis is the process of finding the voltages across, and the currents through, every component in the network.

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49 votes
2 answers
72k views

STM32 Understanding GPIO Settings

In STM32 Standard Peripheral library, we need to configure the GPIO. But there are 3 functions which I not sure how to configure them; GPIO_InitStructure.GPIO_Speed GPIO_InitStructure.GPIO_OType ...
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40 votes
13 answers
10k views

Why can current only flow in loops? [duplicate]

In the following image: Why can't current flow across the following wire? It's a simple question, but I've kind off always wondered. Thanks!
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40 votes
5 answers
38k views

Why use complex numbers to represent amplitude and phase of AC

Why is it that in AC circuits, sine waves are represented as a complex number in polar form? I don't logically understand from a physical perspective why there is an imaginary part at all. Is it ...
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38 votes
3 answers
15k views

How do Circuit Simulators actually work?

I recently had the opportunity to play around with LiveWire, which is a circuit simulator and began wondering how exactly they computed the voltages across each component and the current going through ...
37 votes
5 answers
33k views

Why is the time constant 63.2% and not 50% or 70%?

I am studying about RC and RL circuits. Why is the time constant equal to 63.2% of the output voltage? Why is it defined as 63% and not any other value? Does a circuit start working at 63% of output ...
34 votes
8 answers
3k views

Two black boxes display the same impedance at all frequencies. Which has the single resistor?

Two black boxes display the same impedance at all frequencies. The first contains a single 1 Ohm resistor. Each end is connected to a wire, so that two wires protrude from the box. The second box ...
30 votes
7 answers
9k views

Why is root mean square used when calculating average power, and not simply the average of voltage/current?

$$P = I_{\text{eff}}^2 \times R$$ where \$I_{\text{eff}}\$ is the effective current. For power to be average \$I\$ must be average current, so I am surmising that the effective current is the average ...
27 votes
6 answers
9k views

What is a flip flop?

There seem to be a number of different definitions of flip-flops and latches out there, some of which are contradictory. The Computer Science text book for the course I teach is probably the most ...
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22 votes
4 answers
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Do electrons actually flow when a voltage is applied?

It's said in books that a circuit is a closed path and thus that electrons come back to the source. If that's the case, what would happen when there were an earth fault in a circuit? How would the ...
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22 votes
5 answers
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How can we test the lifespan of electrical components?

We work with some electronic devices in our projects. We are at the stage where we need to create some test strategy to validate the lifespan (e.g. 1 to 5 years) of our devices for which we provide ...
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22 votes
2 answers
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Half-wave diode rectifier - is textbook wrong?

I've noticed that in all resources on diodes and rectifiers, they show the output voltage as the positive half-wave of the input signal. However, that seems wrong. I understand that there's a voltage ...
21 votes
6 answers
6k views

Why would a circuit designer use parallel resistors?

I've been reviewing this reverse engineered schematic of a bmax6 style lipo charger. To my understanding this circuit is used to dissipate excess charge in a cell when balance charging. The circuit ...
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20 votes
5 answers
3k views

What is the true circuit behind an opamp?

So, first year EE student, and I just learned about op-amps. I understand the ideal model, and know how to analyze them, and understand the idea behind them/the circuit that we were shown that is ...
20 votes
3 answers
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I think I found an error in an electronics book. Are my equations correct here?

I'm reading Practical Electronics for Inventors, 4th edition, to freshen up my long forgotten knowledge of electronics. I love the book so far, but I just came across an equation there which seems ...
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19 votes
4 answers
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What is the use of an op-amp whose output and inverting input are connected to ground?

I am in first year of Engineering school and I was given an assignment containing this circuit, which drives pressure sensors in a pitot tube : I am struggling to understand the whole circuit, and ...
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19 votes
9 answers
6k views

Why do I need a ground when simulating a circuit? I thought voltage was relative between two nodes!

Electronics is very new to me. I took the most basic circuit I could think of: A voltage source of 1V and resistor of 1 Ohm As far a I understand I should get a current of (I = V/R) 1 Ampere. But ...
19 votes
4 answers
62k views

How does the tester screwdriver work?

How does the tester screwdriver work? If I put the tester screwdriver inside the "hot wire" of an electrical socket, it lits up if I press my finger against the metal cap on top of the screwdriver. ...
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18 votes
6 answers
4k views

What does this transistor circuit do?

I found a schematic which had this bit of circuitry between the +9 V (which apparently the author assumed to be > 9 V, more like 10-11 V) barrel connector and the +9 V supply rail. I tried to ...
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18 votes
11 answers
3k views

Do working electrical engineers in circuit design ever use textbook formulas for rise time, peak time, settling time, etc

This is a very general question. In undergrad electrical engineering, students are usually taught about step response to LC (second order) circuits. This is usually when many parameters are ...
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17 votes
8 answers
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Why isn't the current split between the transistor and the LED in this NOT transistor circuit?

In the following NOT transistor circuit diagram, the current flows through the 1K resistor and through the LED when the switch is open. This turns the LED on. When the switch is closed, however, the ...
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17 votes
1 answer
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What are the various 'properties' of a diode?

I have come across various properties of a diode, phrased differently in different places (product sheet, everycircuit, etc.). For example: The wavelength is the simplest and that is the color of ...
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17 votes
2 answers
3k views

Under what conditions is the star-mesh transform invertible?

We all know and love the Δ-Y (delta-wye) and Y-Δ (wye-delta) transforms for simplifying three-resistor networks: Image from Creative Commons The Δ-Y and Y-Δ transforms have the nice property that a ...
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16 votes
5 answers
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Op-amp inverter followed by buffer. Why?

In a schematic I've been trying to understand I came across this sub-circuit: It's an op-amp inverter directly followed by a buffer. VIN comes from a DAC in a microcontroller and this circuit ...
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16 votes
4 answers
90k views

Diode Logic Gates

For some reason, I understand transistor logic gates, and I am able to solve problems, but for some reason I do not understand the and / or logic gates constructed by diodes. If someone can explain it ...
16 votes
3 answers
4k views

How do you determine the effective resistance of a finite grid of resistors?

Disclaimer: I am a geophysicist with limited electrical engineering background. I am not sure if this problem is incredibly easy, incredibly complex, or completely nonsensical. My goal: Determine the ...
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15 votes
4 answers
4k views

Shocked by beginner circuit kit

I was trying to visualize a beginner circuit problem on my breadboard and I plugged in my circuit, touched a resistor and got a nasty shock. I am a cs student playing with circuits to build some logic ...
15 votes
8 answers
3k views

Why, in a passive circuit with a sinusoidal input, do all voltages and currents have the same sinusoidal behavior as the input?

I am familiar that in any circuit composed of linear passive elements and a sinusoidal input, all voltages and currents through and across any element will exhibit the same sinusoidal behavior and ...
15 votes
6 answers
2k views

Vintage germanium transistors: How does this metronome oscillator work?

I'm trying to restore and learn from a simple metronome assembled by my uncle in the 60's. It has a nice sounding beat and used to work until very recently — although unstable. I've ...
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15 votes
4 answers
2k views

Digital Logic circuit - exam question

I have a question from exam that I failed to solve: I need to build a digital logic circuit that is receiving 4 bit number and return true if the number is ...
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15 votes
3 answers
2k views

Tips on analyzing circuit with multiple op-amps and bjts

In a homework exercise I need to sketch the Vout-vs-Vin graph, having it first obtained analytically. I know that Ur and Vin are both nonnegative, and the circuit is shown here: It seems like there ...
14 votes
4 answers
13k views

Using diode mode on my multimeter to debug circuits. A good idea?

I've seen a few YouTube videos where the presenter, who appears to be experienced in board repair of Apple (and presumably other) circuit boards recommends to use your multimeter in "diode mode" to ...
14 votes
6 answers
1k views

Can I get help troubleshooting a simple hobby electronics circuit? Multimeter not measuring current drawn

I am following the experiment in the popular electronics book - "Make: Electronics third edition". However, when replicating one of the experiments mentioned in the book (specifically ...
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13 votes
9 answers
11k views

If a circuit only has a current source and no voltage source where does the voltage come from to supply the circuit?

For example this circuit, A current source is something with would alter the voltage across it to meet a certain current. But where is there a voltage source to do this or even have a voltage at Vx. ...
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13 votes
2 answers
2k views

What is wrong about this application of Kirchhoffs Current Law?

At a recent exam I had this very simple problem concerning Kirchhoffs Laws: I am concerned with problem c Now my understanding of this is: I can combine both nodes, and since all currents in the ...
13 votes
2 answers
4k views

What is the role of the transistor and diode in a soft start circuit?

Please can someone explain the purpose of both the transistor and diode in this soft start circuit
13 votes
4 answers
11k views

A 1USD 11W led bulb circuit and parts analysis

I know this is not a huge deal, but still I want to do it because for Three reasons: 1, it only costs 1 usd. Yep, this is a very cheap led bulb, and I need to take it apart to see if it's trust worthy....
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12 votes
5 answers
3k views

Why are crystal oscillators used in clocks instead of RLC circuits?

The timing of quartz clocks is regulated by a crystal oscillator. This crystal oscillator effectively forms an RLC circuit. If this is so, what properties does a crystal oscillator have that makes ...
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12 votes
3 answers
2k views

Internal resistance of a battery

I am trying to figure out where I went wrong on the following problem: simulate this circuit – Schematic created using CircuitLab The two batteries are identical, and each has an open-...
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12 votes
2 answers
31k views

How do I use superposition to solve a circuit?

Yes, this is a pedagogical question. While answering another recent question, I wanted to refer the OP to concise instructions for using superposition to solve circuits. I found that all the easily ...
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11 votes
8 answers
6k views

Saving data without a microcontroller?

Is there a way to save voltage data directly (without a microcontroller) to anywhere, like EEPROM, SDCARD, etc.? For example, I am using an MPX pressure sensor which gives 0V to 5V analog output. ...
11 votes
6 answers
19k views

Why can I use P = I²R but not P=V²/R when calculating energy lost in a circuit?

I am working through a book of problems and am confused by the answer to this one: A 12 V battery supplies 60 A for 2 seconds. The total resistance of the wires in the circuit is 0.01 Ohm. Q1. What ...
11 votes
3 answers
2k views

Do electrons actually jump across contacts?

When we connect two conductors together in a junction, do electrons actually move from one conductor to another? Does it also affects the masses of the two conductors?
11 votes
3 answers
2k views

How do I do basic circuit analysis with resistors rated in watts instead of ohms?

In my electrical circuits class, we've spent the last six weeks learning circuit analysis with resistors rated in ohms. Now, out of the blue, every question on the next practice exam has the resistors ...
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11 votes
2 answers
9k views

Inductor equivalent of capacitor's charge

Because inductors share similar equations in their charging/discharging cycles, I am wondering if inductors have something like charge. Capacitors have capacitance and charge while an inductor has ...
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11 votes
4 answers
1k views

Night light broke after trying to dim LEDs

I purchased a cheap night light that plugs directly into a 240V wall outlet. It has three color changing LEDs. The problem was, those LEDs were way too bright. I decided to modify that night light a ...
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11 votes
7 answers
2k views

Proof that every circuit with diodes has exactly one solution

Consider an electronic circuit consisting of linear components plus a number of ideal diodes. By "ideal" I mean they can either be forward-biased (i.e. \$v_D=0\$ and \$i_D\geq 0\$ ) or reverse-biased (...
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10 votes
4 answers
3k views

The Intuition for RLC circuits

I'm reading through Hayt's Engineering Circuit Analysis 9e and it does a fairly good job of giving the intuition for "where" the energy is going in a damped RLC circuit, but I'm hoping that someone ...
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10 votes
4 answers
5k views

Why exactly does maximum power transfer happen at 50 ohms (matched impedance)?

As the title mentioned - I am not sure why exactly the maximum power delivered to the load will be max when R_L is 50 ohms. If I guess why, it's because if the resistance was greater than 50 ohm then ...
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10 votes
4 answers
2k views

How to compensate noise at the output of logic gates?

I am simulating 74HC logic family on LTSpice. The output of inverters and D-Flip-Flop are normal, but the output of NAND and AND are noisy . How can I compensate or filter that noise? What kind of ...
10 votes
4 answers
3k views

For this Art of Electronics circuit, why aren't the transistors specified? And what transistors do I use?

If I were going to EE school, then there would be a lot of knowledge transferred just by going through all of the usual things -- labs, homework, exams, etc. In teaching myself, it's so hard when they ...

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