All You Need to Know About Capacitors

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Are you planning to work with capacitors on your next project and need a little bit of an insight about these little packages of awesomeness? If yes, then you’re at the right place! Read on to know everything about a capacitor, ranging from its basic working principle till using it incircuits.

Black Transistor Beside Capacitor · Free Stock Photo

What Is a Capacitor?

In simple words, a capacitor is an electrical charge storing element used in circuits. It is a passive electronic component and, just like resistors and inductors, is used in every other electronic circuit. To remember it better, you can consider the example of a battery. Capacitors store electrical charge just like a battery does and the unit used to measure the amount of charge stored in them is called Farad (F). The capacitors that we usually use in electronic circuits have capacitances in picofarad (pF), nanofarad (nF) or microfarad (μF), as you may have noticed on their outer packaging.

How Is a Capacitor Constructed?

To know how a capacitor works, lets first understand how it is constructed. Essentially, a capacitor is like a sandwich – two metal plates separated by an insulating material called a dielectric. The two metal plates on the outside are connected through terminals to the rest of the circuit while the dielectric acts as a separating layer between the two metal surfaces.

Parallel plate capacitor vector drawing | Free SVG

What happens when a DC voltage is applied across the terminals of a capacitor? Positive charges are accumulated on one of its plates and negative charges on the other. An electric field is generated across the plates of the capacitor and the dielectric material reduces the electric field while increasing the capacitance. The intensity of electric field generated and the capacitance also depends on the distance between the two plates as well as their surface areas. The mathematical formula connecting these parameters is:

 Where C is the capacitance, ε is the permittivity of dielectric, A is the area of plates and d is the distance between the plates. Using this equation, the capacitance can be varied during the construction of a capacitor.

What Are the Key Types of Capacitors?

Capacitors can be classified into two groups – Polar and Non-polar.

Polar Capacitors

As the name suggests, this type of capacitor has a certain polarity associated with its terminals. Its positive and negative terminals need to be considered while connecting it in a circuit, unlike resistors.

The most common type of polar capacitors are the electrolytic ones. These capacitors are cylindrical in shape, with one leg longer than the other one. The longer terminal is positive one while the shorter one is negative. Their polarity is also clearly mentioned on their outer packaging. Always make sure to connect these capacitors the right way or else you might end up with an explosion. We will discuss the right way to connect a capacitor in the next section.

Non-Polar Capacitors

The most common types of non-polar capacitors are ceramic and foil capacitors. Ceramic capacitors are the ones shaped like a miniature pill, usually brown in color while foil capacitors are rectangular blocks of different colors.

Non-polar capacitors, as their name suggests, do not have any polarity just like resistors. Ceramic capacitors are used in places where voltages vary and they available in low capacitance values (usually picofarads and microfarads) but they offer high temperature resistance and low losses. On the other hand, foil capacitors are used in high-voltage applications such as working with the mains voltage. They range from nanofarads to microfarads and offer low losses.

How to Connect a Capacitor?

You should be very vigilant while working with polar capacitors because oftentimes, connecting them in the wrong way leads to explosions. As soon as you pick the capacitor in your hand, inspect its outer covering for its operating voltage and signs of polarity. Right above the negative terminal, you will find a series of minus (-) signs printed in a column. Also, notice that the negative terminal would be shorter than the positive one. This is how you can make sure you know the polarity of its terminals.

When connecting the polar capacitor to a DC voltage supply such as a battery, keep in mind the voltage rating you just read on its covering. Do not exceed the mentioned voltage or you might end up frying the capacitor. When you’re sure about the voltage, then connect the negative terminal of the battery to the negative electrode of the capacitor and similarly, connect the positive terminal of the battery to the positive electrode of the capacitor. Never ever connect a capacitor the other way around because that might permanently destroy the capacitor.

With non-polar capacitors, you don’t need to worry about the polarity of the terminals. You can connect any of its legs to a higher voltage and the other one to a lower voltage.

How to Connect More Than One Capacitors?

There are two possible ways to connect capacitors with each other – in series or in parallel (like resistors). Connecting them in any of the configurations will affect the way their capacitances add up. Let’s look at each of the configurations one by one.

When connecting polar capacitors in series, the negative terminal of the first capacitor must be connected to the positive terminal of the second one and the positive terminal of the second one to the negative terminal of the third one and so on. You can connect as many capacitors as you like in this way. The overall capacitance can be calculated using the following formula: 

Where CTotal is the total capacitance and C1, C2 up to Cn are the capacitances of the n capacitors connected in series.

On the other hand, when polar capacitors are connected in parallel, all their positive terminals must be connected to each other and their negative terminals must be joined to each other. This is how they will be connected in parallel with each other. The total capacitance of n number of capacitors connected in parallel can be calculated as:

CTotal = C1 + C2 + … + Cn

With non-polar capacitors, you don’t need to worry about the terminals, you can simply connect them in series or parallel with whichever terminal you wish.

Applications of Capacitors

Capacitors are used in a multitude of electronic circuits be it microcontroller based circuits or simple electronic circuitry. They are used as coupling capacitors in AC circuits where the DC component needs to be suppressed. Similarly, decoupling capacitors are used to suppress the AC components and only allow the DC component to pass through. Coupling capacitors are usually required between two stages of an amplifier whereas decoupling capacitors are used where only DC voltage is required such as DC power supplies or voltage rails.

Similarly, RF coupling and decoupling requires capacitors. These circuits are generally found in the telecommunication industry, where varying frequencies are used. For this application, ceramic capacitors are the best choice because they work best in RF applications.

Capacitors are also used in many filters, most common of which are the rectifier filters. They are also called “smoothing capacitors” because they smooth out the output rectified signal by getting rid of the unwanted voltage spikes. Signal processing industry uses many different types of filters and the frequency range of these filters is decided by the value of capacitance. Hence, we can say that capacitors play a significant role in the telecommunication industry.

Another application of capacitors is that they are used as a power source in certain circuits. Since capacitors are known for storing charge, they can supply power to circuits but for a very limited time.

Oscillator circuits also use capacitors but in combination with inductors and resistors. We will discuss LC circuits in the last section.

How to Fit a Capacitor to Your Circuit?

To fit a capacitor to your circuit, you must choose a capacitor with a higher voltage rating than the voltage of your circuit. Secondly, if you are planning to build a RF filter circuit, then you must make sure that the tolerance of your capacitor must be the same as stated by the manufacturer because filter circuits require high precision since they allow certain frequencies to pass through them based on the values of capacitance and resistance.

Archivo:Capacitor-symbol-bipolar-El-Cap.svg - Wikipedia, la ...

Symbol of capacitator

If you are a student learning how to work with electronic circuits, we recommend you to first simulate your circuit on a circuit designing software and then actually implement it physically. This would save you from unnecessary accidents and explosions plus you will also save a lot of time.

What Are LC Circuits?

Archivo:Lc circuit.svg - Wikipedia, la enciclopedia libre

LC circuits are one of the most common applications of capacitors. These circuits are a combination of inductors (L) and capacitors (C) connected in series or parallel. These circuits are also referred to as “oscillators” because they oscillate at a certain frequency which is determined by the values of capacitance and inductance used. LC circuits are used where a particular frequency needs to be generated or picked out (filtered) from a group of frequencies. A very common application of LC circuits is the radio, where the channel selector knob varies the LC values to filter out a certain radio station frequency.

File:LC circuit voltage current lapse.svg - Wikimedia Commons

Who knew two metal plates separated by a piece of insulator can be so useful? Despite their minute size, capacitors are an integral part of electronic circuitry and work wonders when connected the right way. All they need is to be handled correctly and placed in the right circuit, with the right components.

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