CAPACITOR

TOPIC:

Capacitor

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Topics:Introduction

Basic structure of capacitor

The characteristics of capacitors

Types of capacitor

Uses of Capacitor

What Is A Capacitor?

Capacitors are two-terminal electrical elements. It is an electrical device consisting of two conductors by an insulating or dielectric medium which carrying equal and opposite charges.

History:

• In October 1745, Ewald Georg von Kleist of Pomerania, Germany, foundthat charge could be stored by connecting a high-voltage electrostaticgenerator by a wire to a volume of water in a hand-held glass jar.VonKleist's hand and the water acted as conductors, and the jar as adielectric.

• Daniel Gralath was the first to combine several jars in parallel into a"battery" to increase the charge storage capacity.

• Benjamin Franklin investigated the Leyden jar and came to theconclusion that the charge was stored on the glass, not in the water asothers had assumed

4)Leyden jars or more powerful devices were used exclusively up untilabout 1900,They weren’t more flexible like today’s.

5)Early capacitors were also known as condensers, a term that is stilloccasionally used today, particularly in high power applications,like automotive systems. The term was first used for this purpose tostore a higher density of electric charge than a normal isolatedconductor. It was found by Alessandro Volta in 1782.

BASIC STRUCTURE OF CAPACITOR

• A basic capacitor has two parallel plates(Electrode) separated by an insulating material called dielectric.

• In the neutral state, both plates have an equal number of free electrons.

• When a voltage source is connected to the capacitor, electrons are removed from one plate and an equal number are deposited on the other plate.

• That moment no electrons flow through the dielectric.

• When the supply is removed from the capacitor, the capacitor retains the stored charge.

• The unit of capacitance is the farad(F).

as(Electrode) Plate 2

Plate 1 (Electrode)

Dielectric material

Basic capacitor construction

The dielectric material is an insulator therefore no current flows through the capacitor.

Storing a charge between the plates

Electrons on the left plate are attracted toward the positive terminal of the voltage source

This leaves an excess of positively charged holes

The electrons are pushed toward the right plate

Excess electrons leave a negative charge

A capacitor obeys coulombs law

+

+

+__

_

Characteristics of Capacitors

There are different kinds of capacitors that have been manufactured. Some of them may have numeric codes or colors, and some may use misleading letters or symbols; each family type of capacitor.

The measurement of the nominal value of the capacitance—which is expressed in picoFarads (pF), nanoFarads (nF) or microfarads (uF)—is marked onto the body of the capacitor in the form of numbers, letters or colored bands. The value on the side of a capacitor may not necessarily be its actual value since the choice of capacitance is determined by the circuit configuration.

Nominal Capacitance(C)

The plus and minus value in resistors is also seen in capacitors, which refers to the extent to which the actual capacitance is allowed to vary from its nominal value. 5% or 10% is the most common tolerance variation for capacitors, and can be as low as 1% for plastic capacitors.

Tolerance(+%)

Working Temperature(T)

The capacitance value of the capacitor can be greatly affected by the change in temperature around the capacitor due to the changes in the dielectric properties. This will also affect the correct operation of the circuit when unnoticed.

dielectric medium, around its edges or across its leads and will, over time, fully discharge the capacitor if the supply voltage is removed.

Leakage Current

Figure 3 refers to the small DC current flow in the region of nano-amps. It is a result of electrons physically making their way through the

Types of CapacitorEach of the different types of capacitors has its own performance parameters and

can be used in different applications. Check out my list to see the best capacitor type for a given application. There are many different types of capacitor that can be

used - most of the major types are outlined below:

Ceramic capacitor

The ceramic capacitor is a type of capacitor that is used in many applications from

audio to RF. Values range from a few picofarads to around 0.1 microfarads. Ceramic

capacitor types are by far the most commonly used type of capacitor being cheap and

reliable and their loss factor is particularly low although this is dependent on the exact dielectric in use.

Electrolytic capacitors are a type of capacitor that is polarized. They are able to offer

high capacitance values - typically above 1μF, and are most widely used for low

frequency applications - power supplies, decoupling and audio coupling applications

as they have a frequency limit if around 100 kHz.

Electrolytic capacitor

Tantalum capacitor

Like electrolytic capacitors, tantalum capacitors are also polarized and offer a very

high capacitance level for their volume. However this type of capacitor is very

intolerant of being reverse biased, often exploding when placed under stress. This

type of capacitor must also not be subject to high ripple currents or voltages above

their working voltage. They are available in both leaded and surface mount formats.

USES OF CAPACITOR

Spike Suppression

Computer Memory

Noise Filtering

Timer Circuits

Condenser Microphones

Supplemental Power Source

USES OF CAPACITOR

interference is AC and the capacitor will conduct this AC to ground before it can reach the radio or amplifier.

A capacitor blocks direct current (DC) but passes alternating current (AC). A capacitor makes a very good noise suppressor because most of the

USES OF CAPACITOR

Capacitors in Parallel CircuitsThe following is the formula for calculating total capacitance

in a circuit containing capacitors in parallel.

CT = C1 + C2 + C3 ...

Capacitors in Series CircuitsFollowing is the formula for calculating total capacitance

in a circuit containing two capacitors in series.

CT = (C1 + C2) ÷ (C1 × C2)

Suppression Capacitors

USES OF CAPACITOR

• Capacitors are installed across many circuits and switching points to absorb voltage fluctuations.

• Among other applications, they are used across the following:– The primary circuit of some electronic ignition modules

– The output terminal of most generators (alternators)

– The armature circuit of electric motors