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

当从RC电路中突然移除直流电源时，该电路便成为无源电路。
假设充满电的电容器的初始电压为 V0，则可求得其初始能量，该能量用于激励电路。
在顶部节点应用基尔霍夫电流定律，并代入各元件上的电流值，可得到一个一阶微分方程。
重新整理各项，进行积分并对两边取指数，可得到电路的自然响应，其中积分常数等于初始电压。
电压随时间变化的图像显示，初始电压随时间呈指数衰减。
时间常数 tau 表示电容器放电至其初始电压的 36.8% 所需的时间。
将 tau 的值代入电压响应表达式后，即可确定电阻中消耗的电流和功率。
对时间积分耗散功率可得到电阻吸收的能量。
随着时间趋于无穷大，该能量趋近于电容器中存储的初始能量，表明电容器的初始能量在电阻器中逐渐耗散。

无源rc电路

RC Circuit without Source

当直流电源（DC）突然与电阻电容（RC）电路断开时，该电路将会变为无源状态。假设在移除电源之前电容器已经变为充满电的状态，则其初始电压（记为V0）可被视为激励电路的初始能量。

在电路的顶部节点处应用基尔霍夫电流定律并代入各元件的电流值，从而得到一阶微分方程。对该方程中的各项进行重新排列、积分，然后在两边取指数，能够以此来确定电路的自然响应。该方程中的积分常数等于其初始电压。

电压与时间关系图显示了初始电压会随时间呈指数的趋势进行衰减。这意味着电容器上的电荷会逐渐减少，从而降低了其两端的电压。

电路的时间常数用希腊字母tau(τ)来进行表示，以此来表示电容器放电至其初始电压的36.8%所需的时间。该时间常数通常在确定电容器的放电速率以及电路响应变化的速度方面起着至关重要的作用。

将tau值代入到电压响应表达式中，可以计算出流过电阻器的电流以及电阻器中所消耗的功率。电阻器中所消耗的功率是能量以热能的形式发生损耗的速率。

对随时间消耗的功率进行积分即可得出电阻器所吸收的总能量。随着时间的流逝，该能量最终会接近存储在电容器中的初始能量。这意味着电容器的初始能量会逐渐消散在电阻器中，最终会将该电容器中的电荷耗尽。

总之，提供了解去除直流源后电阻电容电路可以为了解这些电路的瞬态响应提供有价值的见解。这些知识对于信号处理、电力电子和通信系统等应用中的电路设计和分析是至关重要的，其中电容器的快速充电和放电是一个基本过程。

无源RC电路

当直流电源突然从RC电路中断开时，该电路变为无源电路。  
假设电容器充满电后的初始电压为……

Education

教育

JoVE Core

Electrical Engineering

电气工程

Unit 1

第一单元

First and Second-Order Circuits

一阶与二阶电路

KEY TERMS AND CONCEPTS

关键术语与概念

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