What is a capacitor?

A capacitor is a passive electrical device that can store electrical energy for a shorter period of time. You can consider the capacitor as a small battery, but unlike typical batteries, it can’t produce electricity. It can only hold some charged particles for a brief amount of time after charging it from a power source. The amount of charge a capacitor can hold is known as capacitance. And it is denoted by farad.

What does it do?

The most basic construction of a capacitor consists of two parallel metal plates usually known as conductors which are separated by a dielectric material such as glass, ceramic etc. these conductors are extended to the outer shell and this is where we apply the input voltage.

There are two types of capacitor that we generally use,

●     Ceramic capacitor

            Ceramic capacitors generally have low capacitance and they are not polarised. They exhibit large nonlinear changes against temperature and as a result are used as decoupling or by-pass capacitors

●     Electrolytic Capacitor

            The electrolytic capacitors on the other hand are polarised and there is a marking on it that indicates the polarity. They are generally used when very large capacitance values are required. One main disadvantage of electrolytic capacitors is their relatively low voltage rating. Also due to the polarisation of electrolytic capacitors, it can’t be used on AC supplies. Even in the DC circuit If connected inversely it can break down the insulating oxide layer and cause permanent damage. Electrolytic capacitors generally come in two basic forms; Aluminium Electrolytic Capacitors and Tantalum Electrolytic Capacitors.

How does it work?

When we connect a voltage source across the capacitor, the conductor terminal is attached to the positive terminal of the source becomes positively charged, and the conductor connected to the negative terminal of the source becomes negatively charged.

Because of the presence of dielectric in between the conductors, ideally, no charge can migrate from one plate to another.

So, there will be a difference in charging level between these two conductor plates. Therefore an electric potential difference appears across the plates.

The charge accumulation in the capacitor plates is not instantaneous rather it is gradually changing.

The voltage appears across the capacitor exponentially rises until it becomes equal to that of the connected voltage source.

Where to use it?

Electrolytic Capacitors are mainly used in the DC power supply circuits due to their large capacitance and small size. It is used to eliminate ripples. If a line carrying DC voltage has ripples or spikes in it, a big capacitor can even out the voltage by absorbing the peaks and filling in the valleys.

Capacitor is used in the analog circuit to block the passage of DC current and to filter the AC signal.

Capacitors used as a charging unit or discharge unit in power consuming events like triggering a flash light, ignition etc as a temporary power source.

The reactance of the capacitor decreases as the frequency increases. Therefore in certain applications it is used in parallel with other components to bypass it at a specified frequency.

The ability of capacitor to pass AC signal, allows it to couple a section of an electronic circuit to another circuit.In high speed electronic logic switching causes a draw of significant amount of current which in turn would cause disturbance in the logic voltage level. Decoupling capacitor is typically located very close to the IC output and serves as a local energy source to provide the needed extra current and therefore minimizes the noise and disturbances to the logic signal.

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