Name: rc capacitor discharge after power loss
Uploaded: 2024-04-11T12:48:43.000Z
Duration: 1 min 16 s
Channel: JoVE

Lorsqu’une source CC est retirée brusquement d’un circuit RC, le circuit devient sans source.
En supposant que la tension initiale du condensateur complètement chargé est V0, son énergie initiale, qui stimule le circuit, peut être obtenue.
En appliquant la loi du courant de Kirchhoff au nœud supérieur et en substituant les valeurs de courant aux composantes, on obtient une équation différentielle du premier ordre.
En réarrangeant les termes, en intégrant et en prenant l’exponentiel des deux côtés, on obtient la réponse naturelle du circuit, où la constante d’intégration est égale à la tension initiale.
Le graphique de la tension en fonction du temps montre que la tension initiale diminue de façon exponentielle avec le temps.
La constante de temps, tau, signifie le temps nécessaire au condensateur pour se décharger à 36,8 % de sa tension initiale.
En substituant la valeur de tau dans l'expression de la réponse en tension, le courant et la puissance dissipés dans la résistance peuvent être déterminés.
L’intégration de la puissance dissipée dans le temps fournit l’énergie absorbée par la résistance.
Lorsque le temps s'approche de l'infini, cette énergie se rapproche de l'énergie initiale stockée dans le condensateur, ce qui implique que l'énergie initiale du condensateur se dissipe progressivement dans la résistance.

Aucun conflit d’intérêts n’a été déclaré.

circuit rc sans source

RC Circuit without Source

Lorsqu'une source CC est brusquement déconnectée d'un circuit RC (Résistance-Condensateur), le circuit devient sans source d'alimentation. En supposant que le condensateur était complètement chargé avant que la source ne soit retirée, sa tension initiale, notée V0, peut être considérée comme l'énergie initiale qui stimule le circuit.

En appliquant la loi du courant de Kirchhoff au nœud supérieur du circuit et en remplaçant les valeurs de courant entre les composants, une équation différentielle du premier ordre est obtenue. En réorganisant les termes de cette équation, en intégrant, puis en prenant l'exponentielle des deux côtés, la réponse naturelle du circuit est déterminée. La constante d'intégration dans cette équation est égale à la tension initiale.

Le graphique tension/temps montre que la tension initiale décroît de façon exponentielle avec le temps. Cela signifie que la charge sur le condensateur diminue progressivement, ce qui réduit la tension à ses bornes.

La constante de temps du circuit, représentée par la lettre grecque tau (τ), désigne le temps nécessaire au condensateur pour se décharger à 36,8 % de sa tension initiale. Cette constante de temps joue un rôle essentiel dans la détermination de la vitesse à laquelle le condensateur se décharge et, par conséquent, de la vitesse à laquelle le circuit réagit aux changements.

En remplaçant la valeur de tau dans l'expression de réponse en tension, le courant circulant à travers la résistance, ainsi que la puissance dissipée dans la résistance, peuvent être calculés. La puissance dissipée dans la résistance est la vitesse à laquelle l’énergie est perdue sous forme de chaleur.

L'intégration de la puissance dissipée au fil du temps fournit l'énergie totale absorbée par la résistance. À mesure que le temps se rapproche de l’infini, cette énergie se rapproche de l’énergie initiale stockée dans le condensateur. Cela implique que l'énergie initiale du condensateur se dissipe progressivement dans la résistance, épuisant finalement la charge du condensateur.

En conclusion, comprendre le comportement des circuits RC lorsque la source DC est supprimée fournit des informations précieuses sur la réponse transitoire de ces circuits. Ces connaissances sont essentielles pour concevoir et analyser des circuits dans des applications telles que le traitement du signal, l'électronique de puissance et les systèmes de communication, où la charge et la décharge rapides des condensateurs constituent un processus fondamental.

Circuit RC sans Source

Lorsqu’une source CC est retirée brusquement d’un circuit RC, le circuit devient sans source.
En supposant que la tension initiale du condensateur complètement chargé est ...

Education

Enseignement

JoVE Core

Electrical Engineering

Génie électrique

Unit 1

Unité 1

First and Second-Order Circuits

Circuits du premier et du second ordre

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

rc capacitor discharge after power loss

An RC circuit discharges after the DC source is removed. If the capacitor was fully charged first, its initial voltage, V0, provides the energy that drives the source-free circuit.

Kirchhoff’s current law is applied at the top node of the circuit. The current terms for the resistor and capacitor are then substituted, which leads to a first-order differential equation. Rearranging, integrating, and taking the exponential gives the natural response of the circuit. The integration constant in this expression equals the initial voltage.

The voltage-time graph shows an exponential drop in voltage. As the capacitor loses charge, the voltage across it also falls. The time constant, tau (τ), is the time needed for the capacitor to discharge to 36.8% of its initial voltage. It helps determine how fast the capacitor discharges and how quickly the circuit responds to change.

Using tau in the voltage response expression also allows the current through the resistor to be found. From that current, the power dissipated in the resistor can be calculated. Power is the rate at which energy is lost as heat. When that power is integrated over time, the total energy absorbed by the resistor is obtained.

As time approaches infinity, the energy absorbed by the resistor approaches the initial energy stored in the capacitor. In other words, the capacitor’s initial energy is gradually converted into heat in the resistor until the charge is depleted. Understanding this transient response is useful for analyzing RC circuits in signal processing, power electronics, and communication systems, where capacitor charging and discharging are key processes.

RC Capacitor Discharge After Power Loss

first-order circuits

First-Order Circuits in Flashing Lamps

First-order circuits use a resistor and one energy storage element, either a capacitor or an inductor. They are common in electronic systems and are described by a first-order differential equation that links the input and output signals. One important example is the RC circuit, which uses a resistor and a capacitor. In a relaxation oscillator such as a neon lamp circuit, the capacitor starts charging when voltage is applied. At first, the lamp behaves like an open circuit. When the capacitor...

rc circuit without source

An RC circuit discharges after the DC source is removed. If the capacitor was fully charged first, its initial voltage, V0, provides the energy that drives the source-free circuit. Kirchhoff’s current law is applied at the top node of the circuit. The current terms for the resistor and capacitor are then substituted, which leads to a first-order differential equation. Rearranging, integrating, and taking the exponential gives the natural response of the circuit. The integration constant in...

rc circuit with source

RC Circuit Charging After a DC Step

An RC circuit with a DC source shows how a capacitor charges after a sudden voltage step. The applied source is treated as a unit step function, and the capacitor voltage is the step response of the circuit. This response describes how the circuit reacts right after the input changes. A capacitor cannot change its voltage instantly. So, immediately after the switch closes at t=0, the capacitor voltage stays at its initial value. Kirchhoff’s current law is then applied at that moment and...

rl circuit without source

RL Circuit Decay After Source Removal

An RL circuit begins to decay after the DC source is removed. At that moment, the circuit becomes source-free. If the inductor has an initial current, I0, it also stores initial energy. That stored energy drives the natural response of the circuit. Kirchhoff’s voltage law is applied around the loop. The inductor voltage and resistor voltage are substituted into the equation. This gives a first-order differential equation for the current. Rearranging the terms produces a logarithmic form, which...

rl circuit with source

RL Step Response Under a DC Source

An RL circuit connected to a DC source has a step response that changes over time. The response has two parts: the transient response and the steady-state response. The transient response is the short-lived reaction that happens right after the source is applied. During the transient phase, the current changes exponentially. If the circuit starts with current in the inductor, that current decays toward zero as time goes on. At this stage, the inductor acts like a short circuit, so the source...

design example: frog muscle response

RL Circuit and Frog Leg Current Response

An RL circuit is used to model the frog leg’s response to electrical stimulation. In this setup, the student studies how current changes in a resistor-inductor circuit can trigger muscle contraction. The circuit provides a way to control and measure the electrical impulses involved in the experiment. When the switch is closed, the frog’s leg shows a brief contraction. At steady state, the inductor acts like a short circuit. That lets current bypass the resistor and produces a mild, short...

second-order circuits

RLC Damping and Resonant Frequency

Second-order circuits use two energy storage elements, such as a capacitor and an inductor, to shape how current and voltage change over time. These circuits include RLC circuits, along with RC and RL circuits that have two capacitors or two inductors. Their behavior is described by second-order differential equations that connect the input signal to the output signal. The input usually comes from a voltage source or a current source. The output is often the voltage across the capacitor, the...

series rlc circuit without source

Natural Response of a Source-Free RLC Circuit

A source-free RLC circuit is a series circuit with a resistor, inductor, and capacitor, but no external energy source. It begins with the energy already stored in the capacitor and inductor. That stored energy drives the circuit at first. The circuit is described by a second-order differential equation. This equation shows how the resistor, inductor, and capacitor interact over time. The resistor removes energy from the circuit, so the solution has an exponential form. When the exponential...

types of responses of series rlc circuits

types-of-responses-of-series-rlc-circuits

Damping in Series RLC Circuit Responses

A source-free series RLC circuit shows three response patterns based on damping. The circuit is described by a second-order differential equation. Its complete solution is made from two distinct solutions. Those solutions depend on the roots, which are written in terms of the damping factor and the resonant frequency. When the damping factor is greater than the resonant frequency, both roots are real and negative. This gives an overdamped response. The circuit output decays slowly over time. <br...

series rlc circuit with source

Forced Response in a Series RLC Circuit

A series RLC circuit with a DC source can model an automobile ignition system. The circuit shows how a battery can produce the high voltage needed for a spark. In this case, the input DC voltage acts like a forcing step function. Applying Kirchhoff's voltage law leads to a second-order differential equation. A second-order differential equation is an equation with a term for the second derivative. The form of this equation is very similar to the one used for a source-free RLC circuit, so the...

parallel rlc circuits

Parallel RLC Step Response in Surge Protectors

Parallel RLC circuits help explain how a surge protector works in a street lamp. The circuit model uses a DC input source that creates a step response when the switch is turned on. This setup shows how the lamp’s components can be protected from sudden voltage spikes. When the switch closes, Kirchhoff’s current law is applied to the parallel RLC circuit. That leads to a second-order differential equation. The solution has two parts: a transient response and a steady-state response. The...

second-order op amp circuits

Second-Order Op Amp Low-Pass Filters

Second-order op-amp low-pass filters remove unwanted high-frequency noise from audio signals. They are used in audio systems to refine sound quality. These filters are often built as voltage followers and have two nodes with storage elements. The circuit analysis follows the same basic method used for second-order RLC circuits. In practice, bulky inductors are usually avoided because of their size and weight. For that reason, the focus here is on RC second-order op-amp circuits, which are...

design example: underdamped parallel rlc circuit

design-example-underdamped-parallel-rlc-circuit

Oscillator Design with a Parallel RLC Circuit

A parallel RLC circuit can be designed to work as an oscillator with underdamped behavior. This example targets a damped natural frequency of 4 kHz and a damping factor of 4 radians per second. A fixed resistance of 200 Ω is used as the starting point for the design. The first step is to find the capacitance. The damping factor is the reciprocal of twice the product of resistance and capacitance. Using that relationship, the needed capacitance value can be calculated from the given resistance...

key terms and concepts

Learn how a source-free RC circuit discharges after the DC source is removed, including exponential voltage decay, time constant, current, and energy loss.

RC Capacitor Discharge After Power Loss | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

RC Capacitor Discharge After Power Loss

Description

Transcript

Tags