# Questions tagged [circuit-theory]

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### Norton Equivalent and current convention

Consider that we are trying to find the Norton equivalent of a certain circuit . According to my understanding , while finding the short circuit current or the Norton current , we should point it ...
27 views

### Equivalent circuit with voltage buffer

let's consider this circuit: Consider the node A: it is at GND (0 V) because of the voltage buffer at right. So my question is: is it possible to remove it and to consider the following simplified ...
94 views

### Initial Condition in Series RLC Circuit

I have the following RCL circuit simulate this circuit – Schematic created using CircuitLab After using the Laplace transform my lecture notes mention that we get the following circuit ...
29 views

### Current going into the positive pole of a battery while discharging a capacitor

Please bear with me if this is a fundamental question. Let's suppose we have an RC circuit, charging a capacitor up to the voltage of a battery of 9V. The capacitor is currently at 9V, we switch the ...
38 views

### Electric Power in Frequency Domain

Let's consider an impedance Z inside a certain circuit. Let's suppose that we are working with a generic non periodic signal (so it is possible to analyze the circuit with the Fourier Transform). How ...
90 views

### Dissipation and Impedance

it is known that power losses (which become heat) in circuits are due to resistances, because of Joule Effect. But sometimes I read that dissipation is due to the real part of a certain impedance, and ...
44 views

### Isolated circuits: can their reference voltages (GNDs) be at the same potential?

Suppose there are two independent circuits isolated from each other. If they are isolated, the impedance is very high between them (ideally infinite) and there is no current flowing from one to the ...
104 views

### Current Source and Short Circuit

let's consider this circuit: How can I analyze it? Which is the expression of the current in the short circuit? Is it correct to split the circuit in the following way (I always did it when there was ...
36 views

Can I connect two headphone to each other using a female to female connector and setup communication between the headphones?
30 views

### Why is any general cutset equation a linear combination of fundamental cutsets?

I have currently started studying circuit theory and my professor introduced graphs to form kvl and kcl equations. When we form the cutset matrix using fundamental cutsets it is easy to understand ...
61 views

### PC Racing Pedals

I have very limited knowledge of electrical engineering and mechanics (I'm hoping to learn) so please forgive me if this is a stupid/noobish question. I've been thinking about making a steering wheel ...
39 views

### Current flow on this branch [duplicate]

What happens in this current branch? In circuit analysis how to deal with branches like this?
26 views

### What is the contribution of dependent sources while calculating the Thevenin’s Voltage?

I was solving a problem and while calculating the Thevenin’s voltage the dependent voltage source contribution was not taken into account.Why?What important concept am I missing?
81 views

### NMOS High Side switch circuit solving

I'm trying to get my head around the circuit theory behind the high side NMOS switch, here is the shematics: My question is not about whether this is a good or a bad way to make a high side switch (I ...
236 views

### How does one relate an RC circuit's time domain solution to phasors?

It seems to be a given for phasor analysis that the voltage across a capacitor can be defined as follows: $$V_{C}(t) = V_{A}\cos(\omega t + \phi)\tag{1}$$ Where Vc(t) is the capacitor's voltage at ...
106 views

### Determining the Thevenin Equivalent

How could I proceed with this circuit to determine the Thevenin Equivalent? I have the values of $R_1, R_2, R_3, I_2$ and the time value for g. I first tried to figure out the total voltage for the ...
269 views

### Why the opposite of the passive sign convention is not the active sign convention?

Studying the fundamentals of circuit theory, I was reading the Wikipedia article on the Passive Sign Convention and found out about the Active Sign Convention (ASC). After searching many introductory ...
89 views

### How is voltage divided between two reverse-biased ideal diodes?

Suppose we have two identical ideal diodes (without any resistance or voltage drop). We connect these two diodes in series, in the same direction, and reverse-bias them with voltage V. Now we have two ...
785 views

### mesh analysis with current sources + dependent current source

I need to find Ix with mesh analysis method. I will really appreciate your help. So, I turned Is2 to a voltage source and tried writing equations for a super mesh and KCL. anyway, I miss something in ...
99 views

### What are the initial conditions used to find the coefficients in the current equations?

Suppose a RLC series circuit. R, L and C are in series with a battery and a switch. The switch is open. L and C are discharged. At t=0, the switch is closed and the battery (V1) feeds the circuit. I ...
172 views

### How do I find the current equations for the RLC Series Circuit?

Let's talk about a RLC series circuit. R, L and C are in series with a battery and a switch. The switch is open. L and C are discharged. At t=0, the switch is closed and the battery (V1) feeds the ...
32 views

### Is shorting and removing independent sources related to superposition theorem?

I was looking at a derivation of differential gain for a BJT differential amplifier. Along the derivation the power supply and the tail current sources are nulled. I mean the Vcc is shorted to ground ...
3k views

### How do I really calculate these resistors?

I am learning about it. I would like to focus on this circuit I am trying to calculate R10 and R11. I want Ic = 10 mA. Transistor is 2N2222A. This is an amplifier. If I understood how amplifiers ...
61 views

### Finding the unknowns of a current equation leads to non-sense

Suppose a series RLC circuit that is critically damped. Circuit is RLC in series with a DC voltage source $V_S$ and a switch initially open. Capacitor and inductor are both discharged. at t=0 ...
50 views

### How do I calculate the unknowns of the current equation for a RLC series circuit?

Suppose I was dealing with the following voltage equation for the RLC series circuit: $v(t) = Ae^{m_1t} + Be^{m_2t} + V_s$ To know the values of A and B I would do the two initial conditions: ...
190 views

### multiple RGB LEDs with common resistors for each color

I am modifying a pcb with 9 RGB LEDs having three resistors each normally. I know that it is the proper way of doing it. However what is the disadvantage of connecting them as below? Resistors being ...
137 views

### MCU sinking current from a higher voltage source

In previous designs, I have used an MCU digital output to drive the lower side of a resistor ladder to the supply voltage, to prevent power consumption when the ladder is not being sampled: Schematic ...
330 views

### How to find the value of alpha in this curcuit?

I have tried to solve this way but i am not sure how to proceed from here: [![tried solution]]
416 views

### How to find current in this circuit passing through 4ohm resistor

Below I have added my solution after the question so please let me know how I can solve it after the last step: These steps to follow to solve the question from where i left in my post , FYI :As ...
109 views

### Calculate currents of diodes

simulate this circuit – Schematic created using CircuitLab $$U_{DF}=0.7V$$ Calculate the currents of diodes. I've used KVL and KCL in 3 nodes, and I got $$I_{D1}=0.2mA$$ $$I_{D2}=-0.5mA$$ ...
65 views

### Would a diode with a different forward voltage and response time cause this circuit to behave erratically?

I accidentally substituted diode RS1BB-13-F for S1BB-13-F. RS1BB-13-F's forward voltage is 1.3V, while S1BB-13-F is 1.1V. These substitutions were at D8 and D9 in the schematic (top right corner). ...
803 views

### What happens to Filtered High Frequency Noise?

How to filter out high frequency noise from power supplies has been covered ad nauseum, but no one ever discusses what actually happens to the noise itself. Surely it doesn't just disappear? My ...
254 views

### Step Response of Ideal Inductor with Current Source

I'm taking an electronics course to get a physics minor (I'm an applied math major) and today, the professor shows a diagram of an ideal current source connected to an ideal inductor. Crazy stuff I ...
229 views

### Why are MOSFETs used on the battery gauge lines?

This is from the iPhone 10, previous models didn’t have MOSFETs on the gauge lines so I’m wondering why they’re used now. Is it so the phone can’t boot with just a voltage present from external ...
78 views

### Are GPIO outputs software or hardware controlled?

I’m trying to diagnose an iPhone 6s that’s stuck in a boot loop. iTunes error points to a baseband issue. So I’ve compared to a known working board and found that the PMU_TO_BB_PMIC_RESET_L line (at ...
4k views

### Can a thyristor be built from two transistors?

Supposedly, an SCR/thyristor is just a simple, four layer PNPN semiconductor. If that's the case.. When a circuit calls for a SCR/thyristor, and there isn't one available, can it be substituted by (...
744 views

### LEDs seem to automatically self-regulate to achieve ideal voltage across terminals

Note: the key question is now in bold at the bottom, for the people who have had trouble figuring out what I'm trying to ask. Sorry about the meandering explanation. I've been experimenting with ...
106 views

### Secondary linear lamp circuit interrupter switch

Following on from this answer to a previous question from a while back, I want to add a new lamp (with its own button/switch). The new lamp should be controlled separately (i.e. not controlled or ...
402 views

### Simplest Inverter

Theoretically, what is the simplest inverter circuit possible? I mean, really basic. With the least amount of components. It doesn't have to be nice. It doesn't have to step up the voltage, or ...
2k views

### Definition for self-commutated switches

PSIM (an electronic circuit simulation software package) classifies GTO, IGBT, MOSFET as self-commutated switches. However, I ...
706 views

### What is the simplest possible monostable 555 timer circuit?

Say for instance, the goal is to light an incandescent bulb for x amount of seconds (let's say 20). What is the simplest configuration possible? Of course, simple timer circuits aren't rare, and can ...
42 views

### Nodal Analysis #2 - Where is my mistake?

I am given a problem with its shallow solution (i.e. not all steps/formulas shown). When I tackled the problem (below), my answer didn't match the apparently correct solution. Where is my mistake? The ...
55 views

### Nodal Analysis #1 - Where is my mistake?

I am given a problem with its shallow solution (i.e. not all steps/formulas shown). When I tackled the problem (below), my answer didn't match the apparently correct solution. Where is my mistake? The ...
66 views

### Oscillator circuit operation confusion

In this circuit and explanation, it all makes sense except I'm having a hard time picturing Q2 not turning on until C1 has discharged first. When C1 is discharging through Q1 why doesn't Q2 turn on ...
599 views

### Time delayed deactivation of a circuit

In a simple electronic circuit with a momentary switched LED (or bulb, tube etc.); what can be done to trigger the LED for several seconds before proceeding to break the circuit? In other words; I ...
4k views

### Meaning of Sigma in Laplace transform

I found the question below in a forum and I also have same problem. Unfortunately, there is no answer at all so I will post it here hope someone could make it clear. A gain relation in a circuit of ...
131 views

### Basic circuit analysis - phase shifting

For the part of the circuit of sinusoidal circuit given below, the following data is given (effective values): $$E=10V,I_g=2\sqrt 3 A,I_2=2A.$$ Impedance of conductor is $$Z_C=5\Omega.$$ Current Ig ...
175 views

### Anyone an expert on mobile LCD displays? [closed]

Reason I ask is, I've noticed with water damaged iPhone 6 screens if the pins on the connectors of the screen itself have corroded and you fix them with cleaning and fresh solder or jumper wires 8 out ...