Questions tagged [time-constant]

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2answers
79 views

Finding time constant in terms of R and C

I got a different expression for the time constant than the actual solution. Can anybody tell me where I went wrong? Why is it that in the solution all three resistors were put in parallel? What do ...
0
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0answers
40 views

inductor/coil - time to reach a given current

I understand that there's a simple forumla for calculating the time it takes for an inductor to reach 63.2% of it's maximum current: t = L/R But is there a way to calculate how long it would take to ...
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1answer
48 views

Time constant of inverting amplifier, filter

simulate this circuit – Schematic created using CircuitLab I want to calculate the time constant τ of the filter. Can anybody help me?
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5answers
199 views

why does RC time constant happen to equal 1/e?

I understand that the time constant in AC RC circuits is defined the value of resistance (in ohms) x the value of capacitance (in farads). Indeed, ohms(R) x farads(C) yields time (seconds). $$\tau ...
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1answer
59 views

Finding the time constant of an RL circuit

I've the following circuit: simulate this circuit – Schematic created using CircuitLab And I've to find the time-constant of the voltage across the inductor. I did the following: The voltage ...
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2answers
80 views

Calculating time-constant with z-Diodes

I'm a student in Computer Sciences and am currently preparing myself for an Exam in Electronics. I came across this Exercise: (U_0(t) = 10V), u(0) = 0V) I don't have any solutions for the exercise, ...
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2answers
144 views

Derivation of time constant for single source, single capacitor RC circuit

Take a circuit comprised of resistors, a single capacitor, and a single step response voltage source. Then: Every single voltage and current in the circuit, except at the voltage source, will have a *...
0
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1answer
132 views

Time Constant of a Complex RC Circuit

I'm trying to model a diode as two capacitances, a conductance, and a series resistance, as shown here: In order to generate an expression for the capacitance I'm equating 1/w3db to the time constant ...
0
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1answer
104 views

Frequency vs time constant

What happens when I have a low pass filter with R = 1kΩ C = 0.1 µF and I input a square signal with different frequencies? Will the time constant be the same for all frequencies? τ = 100 µs for 1 kHz ...
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2answers
111 views

What does t2-t1 represents in the expression t2-t1 = RC*ln|9|?

And how do I find t2-t1 with an oscilloscope? I was given the following problem, I derived the expression in the title of the question and I need to use the oscilloscope to find t2-t1... Resistors ...
29
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5answers
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 ...
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2answers
137 views

Iterative simulation of RC low pass filter, strange correction required

To get further understanding in how iterative simulators work, like circuitJS for an example, I decided to make my own of a simple RC low pass filter. The voltage I am interested in is the one across ...
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4answers
2k views

What is time constant in LC circuit?

The excerpt below is from ASDTIC control and standardized interface circuits applied to buck, parallel and buck-boost dc to dc power converters. On page 2, introduction section: The electrical ...
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2answers
321 views

RC circuit charging and discharging by square wave not giving a square wave across input on oscilloscope [closed]

question shifted to Input across RC circuit is not showing a square wave though the input is a square wave as it was unclear
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1answer
516 views

Time constant in an RC circuit

Is it possible for this circuit to have two different time constants? One from 0 to 30µs and the other one from 30µs. I tried to calculate the values and I get τ1=20µs and τ2=...
0
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0answers
197 views

Calculating the time constant for an RC circuit

I have this circuit where \$C1 = 2~\mu F, C2 = 4~\mu F, R1 = R2 = 1~\Omega \$. Here, I want to calculate the time constant of the following circuit. I calculated the equivalence resistance and ...
0
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2answers
422 views

RC time constant changes with introducing LED

I am testing time constants for a capacitor. Practical implementation is almost accurate as theoretical calculation. But the Time const changes(rises) when I introduce an LED in series with R AND C. ...
0
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2answers
209 views

Double CMOS inverter time constant

The problem involves finding the time constant for the circuit that arises when the switch is flipped to the U position. What excactly is happening here? I am having trouble visualizing what is going ...
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2answers
602 views

Precision control of current to an inductive coil (coilgun)

I have students building a coilgun. At first they used a manual switch, despite my suspicion that it would not switch on cleanly. After looking on the oscilloscope at the trace of a one shot, we can ...
0
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1answer
108 views

Working out equivalent resistance

I understand this has been asked before, but I've never been able to find a satisfactory answer to the question I have, which is: in general, how do we treat the dependent sources in the small signal ...
0
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1answer
81 views

LTC3106 solar harvester example - different resistance values but same ratio

I've highlighted the voltage divider on the LTC3106 solar harvester example: The datasheet explains that the RUN pin is connected to a comparator which enables a ...
0
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2answers
461 views

RC time constant calculation

I have a circuit and I need to calculate the RC time constant. Here is the circuit and how I simplified some of the resistors: simulate this circuit – Schematic created using CircuitLab where ...
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3answers
2k views

Step response and time constant of RC circuit with multiple capacitors

I need to find the step response and the time constant of the given RC circuit: : Can anybody please share the method to solve this circuit? Also, if R1=R2=R and C1=C2=C; then is the step response a ...
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1answer
221 views

RC time constant and delay

I understand that for an RC circuit acting as a load of a driver will afftect the delay of the output after the RC load. So as long as RC for different values of R,C are equal, delays are equal, is ...
3
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1answer
157 views

Relaxation oscillator with two time constants

I have the following circuit and I have to find the duty cycle of the output signal and its frequency: I figured out that if \$v_{cond} > 0\$, then D4 will be forward biased and D3 reverse biased, ...
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5answers
9k views

Capacitor across an ideal current source

How long will the capacitor below charge? Given that both the current source and capacitor are ideal. If someone says the capacitor will be charging up to its capacity, what is the capacity of this ...
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2answers
1k views

Effective resistance seen by capacitor

I needed to find time constant of the above circuit. I guess we should first draw small signal analysis. The book found time constant as (RD+RL)*Cc. It says that we can find time constant using the ...
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2answers
2k views

Time for capacitor charging in RLC circuit

Time constant is the time taken by a capacitor to charge to 0.63% of source voltage and in rc circuit time constant is RC. But in series RLC circuit how much time it takes for capacitor to charge to 0....
3
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1answer
119 views

Calculating pulse width

The following circuit is taken from The Art of Electronics book. Assuming the base-emitter voltage drop of 0.6V for both the transistors, the C1 charges to approximately 4.4V (left-to-right) when ...
3
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1answer
452 views

Determination of System poles through open/short circuit time constant technique

I was reading about the open and short circuit time constant technique for estimating the dominant and non-dominant poles of the system respectively. For the dominant pole (open circuit time constant) ...
0
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2answers
637 views

time constant confusion of second order system

For first order systems, its easy to get the time constant by using thevenin concept. Suppose i have a second order system ,for example consider a two stage cascaded LOW PASS FILTER with identical ...
2
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1answer
405 views

Open-circuit time constant method

Can anyone explain how Rgd is obtained? I plugged both Ix into Rgd expression but did not get the correct result. here is my attempt I cannot proceed. What did I do wrong? How can I get rid of Vx ?
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3answers
8k views

What will be the time to charge a capacitor if there is no resistance?

A capacitor charges to 63% of the supply voltage that is charging it after one time period. After 5 time periods, a capacitor charges up to over 99% of its supply voltage. Therefore, it is safe to say ...
0
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1answer
270 views

Adding capacitor for faster ADC

Vs = 5V R1 = 50k R2 = 7k (adc internal resistor) C2 = 120pF (adc internal capacitor) I have a big output impedance as R1 at the output of the sensor and i want to connect it to ADC. But max ...
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1answer
2k views

Different time constants for charging and discharging of a circuit with a constant current source and a capacitor

Consider a circuit that only has a constant current source and a capacitor. The voltage across a capacitor is proportional to the integral of the current I, times time. Since the current is constant ...
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2answers
486 views

Calculating resistance and capacitance given the time constant

I'm currently conducting an experiment where I need to determine what a black-box component consists of. After measuring input and output voltage for various frequencies I have so far determined that ...
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3answers
411 views

Simple Capacitor Charging Question

Right, I have a very simple circuit that I aim to use as a delay circuit, everything was going fine until I started to over think it all and now I have totally confused myself and it is slightly ...
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5answers
50k views

Why do farads multiplied by ohms produce a result that has a unit of seconds?

Why is the time constant (RC) measured in seconds even though the units are farads x ohms? This is to fulfill my own curiosity as I haven't had much luck at finding the answer. I would be most ...
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3answers
5k views

Different time constants for charging and discharging of modified RC circuit

I recently performed a test in an electrical measurements lab which left me confused. I measured the response of the following circuit: And obtained the following output: According to my professor, ...
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3answers
701 views

Time constant for RC common emitter circruit

Here is a simple circuit for common emitter. Is the time constant for charging \$C_1\$ equal to \$C_1R_2\$? It doesn't seem logical that \$R_1\$ would influence the charging of \$C_1\$, since it's ...
2
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1answer
3k views

Opamp relaxation oscillator (single supply)

I simulated and built current circuit. What I got was a rectangular wave generator with a duty cycle significantly lower than 50%. Than I made R3 = R4 and got 50% duty cycle. I managed to think ...
0
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1answer
563 views

Understanding rc time constant

I get that if you put a resistor in series with a capacitor and add DC voltage, the cap will take longer to charge up. How can I calculate, how long it takes for the capacitor to charge up/discharge ...