# 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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### 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 ...
51k 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 ...
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 ...
11k 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 ...
14k 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 ...
6k 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 ...
6k 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 ...
2k views

### 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 ...
2k views

### 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 ...
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 ...
2k 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 ...
4k 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 ...
44k views

### 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 ...
3k views

### 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 ...
2k 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 ...
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 ...
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 ...
1k 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 ...
6k 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. ...
41k 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. ...
3k 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
2k 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 ...
2k 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 ...
5k 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. ...
8k 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 ...
1k 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 ...
1k 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-...
3k 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....
1k views

### Hacking Circuits Together Using Existing Schematics

I am working on a prototype using existing breakout boards from open source hardware manufacturers (Sparkfun, Adafruit, Teensy etc...). Everything is going great! I am at the stage where I'd like to ...
8k views

### How is current split with two parallel LED's?

I have two LED's in parallel with different forward voltages, and want to know how much current flows through each of them. They have one series resistor connected before being split. Like so: As LED'...
1k views

### Help understanding this LED lighting transistor circuit

I simulated this circuit from a reference design but I'm not entirely sure how it's working or how you would go about designing such a thing. In simulation it looks like it's designed to hold the ...
1k views

### What role does the capacitor and the resistor play in the following circuit?

I opened up an LED light bulb at my home and sketched its circuit diagram as follows: I don't understand what the initial 470n capacitor connected to the live wire and the final 100ohm resistor ...
7k views

### Are there any quick way to tell if a filter is high-pass, low-pass, or band-pass, just by looking at the transfer function in the s domain?

How can I quicly determine if a given filter's transfer function like: $H(s)=\frac{k}{s^2+ks}$, or $H(s)=\frac{1}{s+k}$, is either a low-pass, high-pass, or band-pass ?
27k 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 ...
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 (...
503 views

### Finding the Transfer Function of Spring Mass Damper System

I have been going through Ogata Modern Control Engineering book and working through several exercises to improve my understanding of basic control principles. I came across the following example which ...
425 views

### Beginner electronics hobbyist needing my schematic looked over

I only very recently started getting into electronics as a hobby, and the little amount of theory I got in college did help, when I actually started remembering things :P Anyway, my next project is a ...
3k views

### What is AC actually?

What is actually alternating current (AC)? And direct current (DC)? I've been reading several books about basic electric circuits analysis and they are contradictory. Some books say that AC is the ...
2k views

### Why doesn't it matter if a resistor is before or behind an LED wrt voltage drop?

I have read that current is always the same within a circuit, but as far as I understood voltage is not. Every electronic part I use lowers the voltage more or less, even simple wires do this. So far, ...
2k views

### Does this circuit problem have a solution without an Op-Amp?

I was going through the definition of a voltage follower in this site http://www.learningaboutelectronics.com/Articles/Voltage-follower And a basic problem was presented, and an op-amp voltage ...
2k views

### Emergency light circuit - What is the function of resistors, diodes and capacitor?

simulate this circuit – Schematic created using CircuitLab I found this circuit on the internet. In this, the bulb glows when AC supply is OFF and bulb goes off when AC supply is present. So, ...
6k 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 ...
68k 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 ...
1k views

### What are the limiting factors of these op-amps?

I designed a multiple feedback band pass filter ...
284 views

### Calculate the resistances of all the possible connections inside a N-terminals black box based on measurements between terminals

Although it would seem that this is not the right SE for this thread since it is about creating an algorithm, the problem is actually about finding a systematic approach to the simplification of ...
2k views

### What is the silver strip behind crystal in the PCB?

Consider: I came across a PCB, and I found a silver strip behind the crystal. What is that strip? Has anyone used it?
2k views

### Does a diode block current but not voltage?

When running this test circuit on CircuitLab and my expected result was that only M1 would open but then i noticed that the M4 mosfet is also open even though there is a diode between it and the the ...
2k views

### Logic level converter using Transistors

I am trying to make a logic level converter using transistor BC547. This is to convert Voltage level of Rpi Gpio from 3.3 to 5V. I have wired the circuit according to this diagram: I have done this ...
I have found a plenty of documents and books that model how the voltage across a capacitor behaves within a transient RC circuit, using the following equation: $$V_C=V_{MAX}(1-e^{-t/RC})$$ ...