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Questions tagged [circuit-theory]

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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 ...
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2answers
72 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 ...
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1answer
77 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 ...
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2answers
50 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 ...
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1answer
64 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 ...
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1answer
27 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 ...
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3answers
2k 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 ...
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1answer
55 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 ...
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1answer
40 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: ...
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3answers
71 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 ...
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1answer
65 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 ...
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0answers
71 views

When deriving the instantaneous power equation for an AC power system, I get different answers depending on how I model the V & I signals. Why?

When I define \$v(t)\$ & \$i(t)\$ like this: \$v(t)=V_m\cos(\omega t)\$ \$i(t)=I_m\cos(\omega t-b)\$ where \$V_m\$=Voltage Amplitude, \$I_m\$=Current Amplitude, \$\omega\$=rotational frequency,...
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3answers
209 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][2]][2]
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3answers
90 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 ...
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2answers
87 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 $$I_{D1}=0.2mA$$ $$I_{D2}=-0.5mA$$ ...
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3answers
57 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). ...
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2answers
366 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 ...
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1answer
139 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 ...
0
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1answer
118 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 ...
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0answers
76 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 ...
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2answers
3k 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 (...
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7answers
681 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 ...
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1answer
86 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 ...
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4answers
319 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 ...
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4answers
1k views

Definition for self-commutated switches

PSIM (an electronic circuit simulation software package) classifies GTO, IGBT, MOSFET as self-commutated switches. However, I ...
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0answers
89 views

Filament and brightness confusion

So I've been reading mixed explanations on the following questions I've been pondering: Does a brighter (incandescent) bulb use thinner more resistance filament or a larger less resistance one? Which ...
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2answers
480 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 ...
0
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1answer
39 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 ...
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0answers
46 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 ...
0
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1answer
63 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 ...
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6answers
313 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 ...
3
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1answer
2k 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 ...
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2answers
98 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 ...
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2answers
151 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 ...
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1answer
94 views

Flow of electricity. Need explanation [closed]

simulate this circuit – Schematic created using CircuitLab People are taught how to calculate this very simple thing, and the calculation goes from source plus to minus, and the diode is there ...
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3answers
116 views

What is the current - voltage relation in a wire?

This is a question from a TV game show. Fill the blank with appropriate words. Current flowing through a wire is ... to the voltage drop across the wire. The answer in the dots is "proportional"....
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1answer
38 views

Network theorem origin

While finding the norton's equivalent curcuit,we 1.find the short circuit current through the load 2.Find the resistance between the two points across which load is connected shorting the voltage ...
3
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1answer
97 views

What hypothesis are needed to support the following argument on a three phase system?

Given the following three-phase system: simulate this circuit – Schematic created using CircuitLab Suppose to set 2 wattmeters as follows: \$P_{21}\$ which measures current \$I_2\$ and ...
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8answers
8k views

Am I insane to question that only with a closed path can electrons move?

First of all let me just state that I do not feel confident enough to tell anyone anything about how electric circuits work or anything about the physics behind them because I simply do not know or ...
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4answers
301 views

Discharging Circuit with LED indicators?

I'd like to create discharging circuit with four LEDs indicating how much charge is left from the discharging battery. It needs to be a low cost solution (no Arduinos; only simple circuit components) ...
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2answers
106 views

What does this circuit show?

I am just starting out looking at more complex circuit diagrams, and I really do not understand what is being shown here My initial guess was that this was a series circuit with the probe (consisting ...
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2answers
96 views

Basic circuit with diodes analysis

I have the following circuit: How to determine the waveform of Vout, maximum values for positive and negative half-period segments, and the average value of Vout? Input voltage Vin has a sinusoidal ...
0
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1answer
501 views

Adding a delay to a door alarm?

Hi guys I saw these window/door alarms https://m.dollartree.com/h5/r/product/Battery-Powered-Window-Alerts/p328789/index.pro at the dollar tree that work off a reed switch. When the magnet bar is ...
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2answers
2k views

Is voltage and current sources linear or nonlinear?

From the circuit theory it is known that an element whose response is linear is called linear element such as resistor, capacitor. For example, in case of resistor the slope between V and I is a ...
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1answer
111 views

capacitive proximity sensor - how does it work

I know 3d printers such as the i3 use a Capacitive proximity sensor to try compensate for the uneven surface of the print bed. for example this one seems to be popular https://www.amazon.co.uk/gp/...
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2answers
265 views

CMRR for an ideal op amp

In the question, he told me from the begging that it is an ideal op amp .. so A(cm) =0 !! How can I find the CMRR then !! I tried to analyze the circuit to be sure!! And i got the same !
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3answers
276 views

Why is the current in this circuit 100mA?

I am just learning electronics and trying to reason some figures I measure in simple circuits. I need a bit of a hand with this one. I have a 3.2V power source, and 2, 1 ohm resistors wired in ...
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1answer
934 views

RL circuit Step-Response Equation explaination

Im having difficulty understanding the integral calculation in number 4. How does (Response) section of "V/L" convert into "V/R"? Where does exponents go? The last equation is from the textbook. *I ...
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2answers
349 views

Simple KVL Problem Not So Simple

We're only a week in to the first EE class here at Uni and I'm already stumped. I can build a power supply in my sleep but anything theory-related turns me upside down. Now, I've done KVL on the ...
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2answers
2k views

First order circuit with t=0+ , t=0-?

Yesterday I tried to solve a question in a second order circuit , but I couldn't ! because I have problem understanding the concept of 0+ , 0- ! So let me try it in a first order circuit , it ...