Explain the Concept of Capacitance in Electronics Circuit Boards

Concept of Capacitance in Electronics Circuit Boards

Along with resistors and inductors capacitors are among the most common passive components that form the circuits we use every day. While the basic concept of storing opposite charges on plates separated by an insulator is easy to grasp, the wide variety of manufacturing techniques and form-factors available in capacitors make figuring out their exact role in a given circuit rather complicated.

The most basic model of a capacitor consists of two thin parallel conductive plates each with an area A displaystyle A and separated by a uniform gap d displaystyle d filled with a dielectric material of permittivity e displaystyle varepsilon . The larger the plates and the closer they are to each other the greater their capacitance, where C displaystyle C is the total charge stored on the plates and the electric field between them.

In this simple model the electronics circuit board on both plates have the same polarity, so no current is flowing between them and they remain at rest. The applied voltage however creates an electric field between the plates. This field causes extra free electrons to collect on the negative plate while stealing them from the positive plate. The difference in polarity between the plates gives rise to an electric potential which can be tapped by connecting the plates to a power source (or to each other via resistance, but this is not typically done in capacitors). The energy of these potential differences represents the stored voltage of the capacitor and is called its capacitance.

Explain the Concept of Capacitance in Electronics Circuit Boards

Capacitors can be combined together in either parallel or series within a circuit. Combining them in parallel increases their surface area A displaystyle A by adding each individual capacitor’s plate and dielectric areas, while combining them in series decreases their overall capacitance because the voltage across each capacitor is divided by the number of plates.

It is important to note that the amount of energy that a capacitor can store is not proportional to its voltage, as is sometimes misunderstood. Instead, it is a function of the plate size and separation and the dielectric material’s relative permittivity. The higher the permittivity of the dielectric material and the closer the plates are to each other the greater the capacitance.

For very large values of capacitance, it is often practical to increase the plate size and/or separation by putting multiple stacks of capacitors together in what is known as a multi-chip package. This allows the maximum possible capacitance to be obtained in a small package and at lower cost.

During operation the electrons in a capacitor will disperse into the surrounding environment and over time they will lose their stored voltage. This process is called self-dissipation and the length of time it takes depends on the type of capacitor and its ambient temperature. This is one of the reasons that it is important to keep capacitors away from sources of heat and in well-ventilated environments.

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