CapacitorsSimilar to resistors, capacitors are also an inevitable component in an electric circuit. Most of you have wondered why these cylindrical-shaped components are used in these circuits. In this article we’ll discuss capacitors, capacitance, what are they, why are they used, and different kinds of capacitors.

A capacitor is a two-terminal passive electrical component that is used to store electrical energy. The basic structure of a capacitor consists of two parallel metal foils and they are separated using an insulator. This insulating layer is called dielectric. These meal foils store electrical energy in the form of electric charges.

Structure of a Capacitor
Source: Google

When a capacitor is connected to a power source, it accumulates energy which can be released when the capacitor is disconnected from the charging source, which is similar to batteries. The difference is that a battery uses electrochemical processes to store energy, while a capacitor simply stores charge. As such, capacitors are able to release the stored energy at a much higher rate than batteries, since chemical processes need more time to take place.

The ability of a conducting body to accumulate charge is called electric capacitance or simply capacitance. The capacitance value tells you the maximum amount of charge the capacitor can store. More capacitance means more capacity and less capacitance means less capacitance. Unit of capacitance is Farad [F].

The capacitance value of a capacitor is obtained by using the formula:

C= Q/V; euation to find capacitance

where C →  capacitance, 

Q →  amount of charge stored on each electrode, and 

V →   voltage between the two electrodes.

From the formula, it can be deduced that 1 F capacitor holds 1 C of charge when a voltage of 1V is applied across its two terminals. In reality, 1F is a lot of capacitance, even 0.001F (1 millifarad → 1mF) is a big capacitor.

The amount of charge stored in each of the plates is equal but they are of different signs.

Structure of Capacitor with positive and negetive charges.

 

All capacitors share the same basic principle components, but the material choice and configuration can vary widely. 

Symbol for capacitor

There are two common ways to draw a capacitor in a schematic. 

The capacitors symbol consists of two parallel lines which actually represent how the capacitor is made. This symbol is used for unpolarised capacitors. Another symbol that is used has a curved line indicating the capacitor is polarized.

Representation of a Capacitor (Symbol)

How a Capacitor Works

Electric current is the flow of electric charge. When current flows into a capacitor, the charges get “stuck” on the metal plates because they can’t get past the insulating dielectric. Electrons — negatively charged particles — are sucked into one of the plates, and it becomes overall negatively charged. The large mass of negative charges on one plate pushes away like charges on the other plate, making it positively charged.

Structure of Capacitor with positive and negetive charges.

The positive and negative charges on each of these plates attract each other because that’s what opposite charges do. But, with the dielectric sitting between them, as much as they want to come together, the charges will forever be stuck on the plate (until they have somewhere else to go).

For example, in the circuit below, a battery can be used to charge the capacitor. This will cause equal but opposite charges to build upon each of the plates until they’re so full they repel any more current from flowing. An LED placed in series with the capacitor could provide a path for the current, and the energy stored in the capacitor could be used to briefly illuminate the LED.

Charging and Discharging of a capacitor.
Source: learn.sparkfun.com

Combination of Capacitors

Similar to resistors, multiple capacitors can be combined in series or parallel to create equivalent capacitance. 

Capacitors in Parallel

When capacitors are placed in parallel with one another the total capacitance is simply the sum of all capacitances. This is similar to resistors in series.

Capacitors in Parallel and equation to find total capacitance

      CTOT  = C1 + C2 + … + CN-1 + CN

So, for example, if you had three capacitors of values 10µF, 1µF, and 0.1µF in parallel, the total capacitance would be 11.1µF (10+1+0.1).

Capacitors in Series

Similar to resistors added in parallel, the total capacitance of N capacitors in series is the inverse of the sum of all inverse capacitances.

Capacitors in Series and equation to find total capacitance

  1/CTOT  = 1/C1 + 1/C2 + … + 1/CN-1 + 1/CN

Types Of Capacitor

Ceramic Capacitors

Ceramic Capacitors are the most commonly used and produced capacitor out there. The name comes from the material from which their dielectric is made. Ceramics were one of the first materials to be used in the production of capacitors, as it was a known insulator. Ceramic capacitors are usually both physically small and have a small capacitance value. It’s hard to find a ceramic capacitor much larger than 10µF. They are usually the least expensive option too. These caps are well-suited for high-frequency coupling and decoupling applications.

Ceramic Capacitor

Electrolytic Capacitor

An electrolytic capacitor is a type of capacitor that uses an electrolyte to achieve a larger capacitance than other capacitor types. An electrolyte is a liquid or gel containing a high concentration of ions. Almost all electrolytic capacitors are polarized, which means that the voltage on the positive terminal must always be greater than the voltage on the negative terminal. They are commonly made of tantalum or aluminum, although other materials may be used. Since they are polarized, they may be used only in DC circuits.

Electrolytic Capacitor

Supercapacitor

Supercapacitors are used to store extremely large amounts of electrical charge. They are also known as double-layer capacitors or ultracapacitors. Instead of using a conventional dielectric, supercapacitors use two mechanisms to store electrical energy: double-layer capacitance and pseudocapacitance. Double-layer capacitance is electrostatic in origin, while pseudocapacitance is electrochemical, which means that supercapacitors combine the workings of normal capacitors with the workings of an ordinary battery. Supercapacitors are polar devices, meaning they have to be connected to the circuit the right way. The electrical properties of these devices, especially their fast charge and discharge times, are very interesting for some applications, where supercapacitors may completely replace batteries.

Supercapacitor

Mica capacitors

Mica is a group of natural minerals. Silver mica capacitors are capacitors that use mica as the dielectric. There are two types of mica capacitors: clamped mica capacitors and silver mica capacitors. Mica capacitors are generally used when the design calls for stable, reliable capacitors of relatively small values. They are low-loss capacitors, which allow them to be used at high frequencies, and their value does not change much over time. Mica minerals are very stable electrically, chemically, and mechanically. Mica doesn’t react with most acids, water, oil, and solvents.

Mica capacitors

Finding the value of a Capacitor

Ceramic capacitors have two to three digits code printed on them.

  • The first two numbers describe the value of the capacitor.
  • The third number is the number of zeros in the multiplier.
  • When the first two numbers are multiplied with the multiplier, the resulting value is the value of the capacitor in picofarads.

If there are only two numbers,  it means there is no multiplier, Then you just read the value of the first two numbers in picofarads(pF).

For Example, If any capacitor has 10 printed on it: Then its value is 10 PF

For a capacitor with code 104 

First 2 digits: 10

Third digit: 4

Multiplier: 10000

Capacitance:10×10000 = 100000pF

For example

  • 682 = 68x 102 = 6800pF
  • 204 = 20×104  = 200000 pF 
  • 472 = 47×102 = 4700 PF
  • 502 = 50×102 = 5000 PF
  • 330 = 33×100 = 33 PF   [100 = 1]

UNITS

  • 1000 nanofarad(nF) = 1 microfarad(µF)
  • 1 pF = 10-12F
  • Nano= 10-9
  • Micro= 10-6
  • 1 nF= 10-9 Farad
  • 1 µF= 10-6 Farad
  • 1 nF = 1000 pF
  • 1 pF = 0.001 nF

Eg: Convert 15 nF to pF

      15 nF = 15 × 1000 pF = 15000 pF

How to choose the best capacitor

There are different types of capacitors out there, each with certain features and drawbacks which make it better for some applications than others.

When deciding on capacitor types there are a handful of factors to consider:

  • Size – Size both in terms of physical volume and capacitance. It’s not uncommon for a capacitor to be the largest component in a circuit. They can also be very tiny. More capacitance typically requires a larger capacitor.
  • Maximum voltage – Each capacitor is rated for a maximum voltage that can be dropped across it. Some capacitors might be rated for 1.5V, others might be rated for 100V. Exceeding the maximum voltage will usually result in destroying the capacitor.
  • Leakage current – Capacitors aren’t perfect. Every capacitor is prone to leaking some tiny amount of current through the dielectric, from one terminal to the other. This tiny current loss (usually nanoamps or less) is called leakage. Leakage causes energy stored in the capacitor to slowly, but surely drain away.
  • Equivalent series resistance (ESR) – The terminals of a capacitor aren’t 100% conductive, they’ll always have a tiny amount of resistance (usually less than 0.01Ω) to them. This resistance becomes a problem when a lot of current runs through the capacitor, producing heat and power loss.
  • Tolerance – Capacitors also can’t be made to have an exact, precise capacitance. Each cap will be rated for its nominal capacitance, but, depending on the type, the exact value might vary anywhere from ±1% to ±20% of the desired value.

Application of Capacitor

Capacitors in Loudspeakers

Capacitors help supply loudspeakers with a steady signal. For instance, if the bass level in a particular song increases very quickly, there may not be enough voltage available to power the speaker to the levels indicated by the audio signal. In such cases, capacitors can help out in the short term by lending their charged energy.

The capacitor in series with the loudspeaker also blocks DC current which could potentially destroy both the amplifier and the speaker. The purpose of the series capacitor is to act as a high-pass filter so that the detector only receives the AC voltage across the motor’s terminals, not any DC voltage.

Capacitors as Sensors

Capacitors are used as sensors to measure a variety of things, including air humidity, fuel levels, and mechanical strain. The capacitance of a device is dependent on its structure. Changes in the structure can be measured as a loss or gain of capacitance. Two aspects of a capacitor are used in sensing applications: the distance between the parallel plates and the material between them. The former is used to detect mechanical changes such as acceleration and pressure. Even minute changes in the material between the plates can be enough to alter the capacitance of the device, an effect exploited when sensing air humidity.

Conclusion

In this article, you have learned about capacitors, different types of capacitor, the uses of capacitors, and how to calculate the value of a capacitor

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