Capacitor is an element that stores electrical charge. The capacitor consists of two close conductors (usually plates) separated by a dielectric surface. Once attached to the power source, the plates accumulate electrical charge. One plate accumulates positive load, while the other plate accumulates negative load.
The capacitance is the amount of electrical charge deposited at a voltage of 1 Volt in the capacitor.
The capacitance is expressed in units of Farad (F).
The capacitor disconnects current in circuits of direct current (DC) and short circuits in circuits of alternating current (AC).
In a diagram, there are two common ways to draw a capacitor. We always have two terminals that link to the rest of the circuit. The capacitor symbol consists of two parallel lines, either straight or curved; both lines should be parallel to each other, near, but not touching (this is actually representative of how the capacitor is made.
Not every capacitors is created equal. To have a particular capacitance, each capacitors is made. A capacitor’s capacitance tells you how much charge it can store, more capacitance means more charge storage capacity. The standard capacitance unit is called the farad, abbreviated F.
It turns out a farad is a lot of capacitance, even a big capacitor is0.001F (1 milifarad— 1mF). Typically you will see a pico-(10-12) to microfarad (10-6) range of capacitors.
You start talking about special caps called super or ultra-capacitors when we get into the farad to kilofarad capacity range.
Types of Capacitors-
There are all sorts of capacitor types out there, each with some benefits and drawbacks that make it better than others for certain applications. There are a few factors to consider when deciding on capacitor types:
Size – Size in both physical volume and capacity.
Maximum voltage-The maximum voltage that can be dropped across each capacitor is classified. Some capacitors may be classified as 1.5V, others may be classified as 100V. Usually exceeding the maximum voltage will result in the capacitor being destroyed.
Current leakage-Capacitors are not flawless. Each cap is likely to leak any tiny amount of current from one terminal to the other through the dielectric. This tiny current loss is called leakage (usually nanoamps or less). Leakage allows the energy stored in the capacitor to drain away slowly, but surely.
Equivalent Series Resistance (ESR) — A capacitor’s terminals are not 100% conductive, they will always have a slight amount of resistance (usually less than 0.01). When a lot of current passes through the cap, this resistance becomes a problem, causing heat and power loss.
Tolerance-It is also impossible to make capacitors have an accurate, precise capacity. Can limit will be valued for its nominal strength, but the exact value can vary from ±1% to ±20% of the desired value depending on the type.
The ceramic capacitor is the most widely used and manufactured capacitor out there. The name comes from the material that makes up their dielectric.
Ceramic capacitors are usually small physically as well as capacitance-wise. Finding a ceramic capacitor that is much larger than 10μF is difficult. A ceramic surface mount cap is commonly found in a small package of 0402 (0.4 mm x 0.2 mm), 0603 (0.6 mm x 0.3 mm) or 0805. Through-hole ceramic caps typically look like small bulbs with two protruding terminals (usually yellow or red).
Ceramics are a more near-ideal capacitor (much lower ESR and leakage currents) compared to the equally popular electrolytic caps, but their small capacitance may be limited. They are usually the least expensive option too. Such caps are ideal for applications of high frequency coupling and decoupling.
Aluminum and Tantalum Electrolytic-
Electrolytics are great because in a relatively small volume they can pack a lot of capacity. If you need a 1μF-1mF capacitor, you will most likely find it in an electrolytic form. Due to their relatively high peak voltage levels, they are particularly well suited to high-voltage applications.
The most popular of the electrolytic family, aluminum electrolytic capacitors, usually look like small tin cans, with both leads extending from the bottom.
Unfortunately, electrolytic caps are usually polarized. We have a positive pin— the anode— and a negative pin called the cathode. The anode must be at a higher voltage than the cathode if voltage is applied to an electrolytic cap. An electrolyte capacitor’s cathode is usually identified by a’-‘ label and a colored strip on the shell. As another indication, the anode leg may also be slightly longer. They can fail spectacularly (making a pop and bursting open) and permanently when voltage is applied in reverse on an electrolytic cap. An electrolytic can behave like a short circuit after bursting.
Also known for leakage, these caps allow small amounts of current (on the order of nA) to flow from one terminal to the other through the dielectric. This makes electrolytic caps less than suitable for energy storage, which, despite their high capacity and voltage level, is unfortunate.
Look no further than supercapacitors if you’re looking for a capacitor designed to store energy. These caps are specially designed in the range of farads to have very high capacity.
Supercaps can’t handle very high voltages, although they can hold a huge amount of charge. Only 2.5V max is rated for this 10F supercap. Anything more is going to destroy it. Super caps are usually placed in series to achieve a higher voltage rating (while reducing overall capacity).
Supercapacitors ‘ main application is to store and release energy, such as batteries, which are their main competition. Although supercaps are not capable of holding as much energy as a battery of equal size, they can release it much faster and have a much longer lifespan.
Electrolytic and ceramic caps cover about 80% of the capacitor types out there (and only about 2% supercaps, but they’re good!). Another common type of capacitor is the film capacitor, which has very low parasitic losses (ESR), which makes them great to deal with very high currents.
There are plenty of other less popular capacitors. Variable capacitors can provide a variety of capacitances, making them a good alternative to variable resistors in tuning circuits. Twisted wires or PCBs may generate capacitance (sometimes unwanted) because each one consists of two independent conductors separated by an insulator.
Capacitors in Parallel-
When capacitors are placed in parallel, the total capacitance is simply the sum of all capacitances. This is similar to how, resistors connect,in series.
For example, if you had three parallel capacitors of 10μF, 1μF, and 0.1μF, the total capacitance would be 11.1μF (10 + 1 + 0.1).
Capacitors in Series-
Just as resistors are a pain to attach in parallel, once put in series, capacitors become funky. The maximum capacitance in series of N capacitor is the inverse of the number of all reverse capacitances.
If you only have two capacitors in series, you can calculate the total capacitance using the “product-over-sum” method:
If you have two equally valued capacitors in series, take the formula further, the maximum capacitance is half of their value. Two 10F supercapacitors in series, for example will produce a maximum capacitance of 5F (it will also have the advantage of doubling the total capacitor voltage level from 2.5V to 5V).
Application of capacitor-
For this nifty little (actually they are usually pretty big) passive component there are tons of applications. Here are a few examples to give you an idea of their wide range of uses:
Decoupling (Bypass) Capacitors
Many of the capacitors you see in circuits are decoupling, especially those with an integrated circuit. The role of a decoupling capacitor is to eliminate high frequency interference in the signals of power supply. They take tiny voltage ripples out of the voltage supply, which might be dangerous to delicate ICs.
In a way, capacitors for decoupling act as a very small local power supply for ICs (the computers are almost like an uninterruptible power supply). If the power supply drops its voltage very temporarily (which is actually quite common, especially when the circuit it is powering constantly switches its load requirements), a capacitor can supply power at the correct voltage for a short time. That’s why these capacitors are also called bypass caps; they can act as a power source temporarily, bypassing the power supply.
The power source (5V, 3.3V, etc.) and ground binding capacitors. Use two or more equal-valued, even different types of capacitors to bypass the power supply is not unusual, as some capacitor values will be stronger than others to filter out certain noise frequencies.
While this may seem to create a short distance from power to ground, only high-frequency signals can run to ground through the capacitor. As desired, the DC signal will go to the IC. Another reason these are called bypass capacitors is because the high frequencies (in the kHz-MHz range) bypass the IC to get to the ground instead of running through the capacitor.
They should always be placed as close as possible to an IC when physically positioning decoupling capacitors. The further away they are, the less effective they are going to be.
Always add at least one decoupling capacitor to each IC in order to follow good engineering practice. Typically 0.1μF is a good choice, or some 1μF or 10μF caps may be applied. These are a cheap addition and help ensure that the chip is not exposed to significant voltage drops or spikes.
Power Supply Filtering
Diode rectifiers can be used to convert the AC voltage to the DC voltage that most electronics require. Yet diodes alone can not transform an AC signal into a clean DC signal, they need capacitor help! A rectified signal like this: by adding a parallel capacitor to a bridge rectifier:
Can be converted to a near-level DC signal like this:
Capacitors are stubborn components, they will always attempt to resist sudden voltage changes. As the rectified voltage increases, the filter capacitor will charge. When the rectified voltage entering the cap starts its rapid decline, the capacitor will access its stored energy bank, and it will discharge very slowly, providing the energy to load. Before the input rectified signal begins to increase again, the capacitor should not discharge fully, recharging the cap. Over and over as long as the power supply is in use, this dance plays out many times a second.
When you break any AC-to-DC power supply, at least one very large capacitor will be identified. Below is a 9V DC wall adapter’s guts. Do you Notice any capacitors in there?
Maybe there are more capacitors than you think! Four tin-can-looking electrolytic caps range from 47μF to 1000μF. A high-voltage 0.1μF polypropylene film cap is the big, yellow rectangle in the foreground. Both ceramics are the blue disc-shaped cap and the small green one in the centre.
Energy Storage and Supply
It seems clear that if a capacitor stores power, just like a battery, one of its many uses would be supplying the energy to a circuit. The concern is that capacitors have a much lower density of energy than batteries; they obviously can not carry as much power as a chemical battery of the same volume (but that distance is narrowing!).
The capacitors ‘ upside is that they usually lead longer lives than batteries, making them an environmentally better choice. These are also able to deliver energy much faster than a battery, making them perfect for applications that require a quick but high power burst. A camera flash could get its energy from a capacitor (which, in effect, a battery was possibly charging).
Also Read – Ohm’s Law – Definition, Formula, Applications
Also Read – Resistor Colour Code