Charging and Discharging of a Capacitor

Discharging and charging capacitors is that the capacitor’s have the capacity to both control and anticipate the pace at which they charge and discharge, which makes them valuable in electronic timing circuits. It occurs when a voltage is applied across the capacitor, and the potential does not immediately rise to the applied value. The charge on the terminals tends to oppose the addition of further charge as it accumulates to its final value. Now that we know the meaning let us look further to see the charging of capacitor’s importance.

Factors affecting the charging and discharging rate:

The following are the factors that influence the rate at which a capacitor can be charged or discharged:

I) The capacitor’s capacitance.

II)The resistance of the circuit that it is charged or discharged through.

Let us go through discharging and charging a capacitor separately to better understand.

Charging a capacitor:

Consider an RC Charging Circuit with a capacitor (C) in series with a resistor (R) and a switch connected across a DC battery supply (Vs). 

When the switch is first closed at zero, the capacitor gradually charges up through the resistor until the voltage across it meets the DC battery supply voltage. The switch is open at time t=0, and the capacitor is fully charged.

 At t = 0, I = 0, and q = 0, these are the circuit’s beginning conditions. When the switch is closed, the time starts over at t = 0, and current flows into the capacitor via the resistor, collecting charge on the capacitor.

At t = 0, the capacitor is in a condition of a short circuit to the external circuit since the initial voltage across it is zero, i.e. (Vc = 0). In this case, the circuit’s maximum current passes through it, with just the resistor R acting as a barrier. 

The voltage drops around the circuit are now calculated using Kirchhoff’s Voltage Law (KVL): The current flowing in the circuit is referred to as the Charging Current, and it can be calculated using Ohm’s law: I = Vs/R.

Vs-Ri(t)-Vc(t)=0.

The potential difference across the capacitor plates gradually develops as it charges up. The time it takes for the charge on the capacitor to reach 63 per cent of its maximum possible voltage in the curve time is equal to one Time Constant, i.e. 0.63Vs.

 The capacitor continues to charge, and the voltage differential between Vs and Vc decreases. The circuit current reduces as well. When the capacitor is fully charged at a condition greater than five-time constants, t =∞, I = 0, q = Q = CV. 

The charging current eventually falls to nothing as the time approaches infinity. The capacitor now works as an open circuit, with the supply voltage value completely across the capacitor as Vc = Vs.

A positive charge emerges on one plate, and a negative charge shows on the other when a capacitor is linked to a battery. The difference in potential between the plates eventually equals the battery’s emf. The entire process takes some time, and an electric current flows between the connecting wires and the battery.

 q= CV(1-e -T/CR)

where q= charge on the capacitor at time t=0

t= time

CR= Time Constant 

Discharging a capacitor 

The charge contained in a capacitor is released when the capacitor is discharged. Let’s look at an example of a capacitor that has been discharged.

In series with a resistor of resistance R ohms, we connect a charged capacitor with capacitance C farad. Then, as demonstrated, we short circuit this series combination by turning on the push switch releasing a capacitor.

The capacitor begins to discharge as soon as it is short-circuited.

Assume that the capacitor has a voltage of V volts when fully charged. The circuit’s discharge current would be − V / R ampere as soon as the capacitor is short-circuited.

However, after the circuit is switched on at t = +0, the current through it is:

i= Cdv/dt

The faster the charging and discharging rate of the Capacitor, the smaller the Resistance or Capacitance, the smaller the Time Constant, and vice versa. Almost all electrical devices contain capacitors. They can be used as a power source. A discharging and charging of a capacitor example is a capacitor in a photoflash unit that stores energy and releases it swiftly during the flash.

Conclusion:

Timing Circuit is the most important and useful advantage of a capacitor’s charging-discharging characteristics. A capacitor is required for the construction of an analogue timer circuit. Capacitors are also used in the flashlight for the camera on our smartphone. When we take images with the camera, the capacitor is first electrified with high energy, and then that energy is applied to the led, which glows with a very high light for a short period. The voltage boosting, signal boosting, and other applications benefit from the capacitor charging-discharging features. A capacitor’s fast charging-discharging characteristics are employed as an energy reservoir in electrical and electronic power supply circuits such as rectifier circuits.