Next to the resistor, the capacitor is one of the most common electronic components out there. And, like resistors, there are many different types of capacitors with each one having its pros, cons, and applications that it’s good for.
A while ago, I published a post about several common resistor types you’re likely to run into.
This post will be similar in that we’ll take a quick look at the common types of capacitors. Topics like the theory behind capacitors or deciphering their markings will appear in future posts.
The post will give a quick over-view of some of the applications for each type of capacitor, but will not go into great detail about the applications (again, this type of info will appear in future posts).
It will also give the reader an idea of the various common capacitors out there, their strengths and weaknesses, and a quick look at their applications. More exotic capacitor types (such as ultracapacitors and supercapacitors) or rare types will probably pop up in a future article.
This should enable one who’s not totally familiar with the various types of capacitors and their uses to hopefully pick the right one for their application.
Also, I suggest bookmarking this post (and the resistor one) as it will serve as a quick reference for the future.
After all, unless you work for a capacitor manufacturer or have a memory like a steel trap, you may find yourself asking questions like …which capacitor has the tolerance I need? Or what’s the voltage range of this type of capacitor?
And trust me; you WILL need to use capacitors in your circuits and creations.
Enough said, let’s dive right into the different types of capacitors.
Two Basic Types of Capacitors
Like resistors, capacitors come in two basic flavors: fixed and variable.
Both operate on the same basic principles.
A fixed capacitor is just like it sounds – its value is fixed and cannot be changed.
Of course, the capacitance of a variable capacitor can be changed.
The type of dielectric (insulating material between the plates) used in the capacitor classifies it.
For variable caps, we have air, mica, ceramic, and plastic.
Fixed value capacitors come in mica, ceramic, plastic, metal film, electrolytic, and more types.
Let’s start by taking a look at two interesting variable capacitors.
If you’re into working on old radios and other older equipment, you’ve likely run into variable capacitors that use air as the dielectric. These are also known as air core capacitors.
These work by keeping one set of plates fixed while the other set connects to a rotating shaft. Rotating the shaft varies the effective area of the plates, thus changing the capacitance. The plates are usually made of aluminum to prevent corrosion. Figure 1 shows this type of capacitor.
Figure 1: old style variable capacitor.
On top, we see the real deal, an actual picture of a variable air core capacitor. The bottom shows a somewhat simplified diagram of how the device works.
These capacitors are very stable over a wide range of temperatures and leakage losses are low. The downside is that they’re big and bulky. Other types of capacitors can achieve the same capacitance in a much smaller package (though they may not be as stable).
Unfortunately, these types of capacitors are showing up less and less these days due to newer technology and the ever increasing demand to shrink electronics. If you come across one, be sure to grab it, even if just for nostalgia’s sake.
The second common type of variable capacitor often finds its home on circuit boards and is the trimmer capacitor.
These usually adjust via a small screw which varies the distance between the plates. They’re good for fine-tuning circuits. Use only a non-metallic tool to adjust these types of capacitors because a metal tool can affect the capacitance making it very difficult to get the right value.
Figure 2 sports a picture of a typical trimmer cap. Note that these capacitors can use several different dielectrics, depending on the application. We’ll go into more detail on specific types of dielectrics when we discuss fixed capacitors.
Figure2: typical PCB trimmer capacitor.
On top, we can see what it looks like. Note that they are usually smaller than it appears in the picture. The bottom gives you a good idea on how the trimmer works.
Trimmer capacitors usually have values in the picofarad range.
Fixed Value Capacitors
Types of Capacitors: Mica Capacitors
Mica capacitors are composed of thin foil plates (usually aluminum or silver) that are alternately stacked to form the two plates of the cap. A thin layer of mica isolates the plates from each other. The whole shebang is sealed inside a protective casing.
The figure below depicts some typical silver mica capacitors.
These caps are very stable and have a good temperature coefficient. The cons are that they usually don’t come in high capacitance values and can be more costly than other types (silver is expensive, ya know).
You’ll find them in high frequency filters, resonance circuits, and even high voltage circuits. They have good insulation, and therefore are able to operate at higher voltages.
Capacitance values range from 1 ρF to about 0.1 µF.
Voltage ratings range from 50 V to 500 V.
Figure 3: silver mica capacitors.
These types of capacitors come in two main varieties: single layer and multilayer.
Ceramic caps (along with electrolytic caps) are the most widely available and popular capacitors.
You might be familiar with the small, round, disc-like capacitors found on many PCBs. These are single layer ceramic capacitors which consist of two plates with a ceramic dielectric in between.
They sport low inductance, so they can find use in high frequency applications.
Using different types of ceramics varies the dielectric constant resulting in several different types of ceramic capacitors.
Therefore, they also have varieties (ultrastable or temperature compensating) that are very stable across a range of temperatures. These can last many years.
The semistable single layer ceramic cap isn’t as temperature stable as the above, but it does have a higher capacitance.
Finally, the HiK ceramic capacitor has a high dielectric constant (and capacitance), but lacks stability and suffers from a phenomenon known as dielectric absorption.
Single layer ceramic caps have a capacitance range of 1 ρF to 0.1 µF.
Voltage ratings range from 50 V to 10,000 V.
Figure 4 shows a typical single layer ceramic capacitor.
Figure 4: single layer ceramic capacitors.
Like mica caps, many ceramic capacitors consist of several alternating layers of ceramic and metal plates. These are the multilayer ceramic capacitors.
They meet the demand for high density ceramic caps, and, like the mica caps, have many layers to boost the total capacitance.
They are also compact and have better temperature characteristics than the single layer variety.
Just like the single layer type of capacitor, they come in ultrastable, stable, and HiK varieties.
Their capacitance ranges from 0.25 ρF to 22 µF depending on the type.
Voltage ratings range from 25 V to 200 V, again depending on the type.
Many surface mount capacitors are multilayer, as we can see in figure 5.
Figure 5: an example of multilayer ceramic capacitors.
There are two main types of electrolytic capacitors: aluminum and tantalum.
Aluminum electrolytics have a chemical paste (the electrolyte) filling the space between their foil plates. When voltage is applied, a chemical reaction forms a layer of insulating material on the positive plate. Because this film is very thin, they can pack a good amount of capacitance in a small package.
The film and the plates are then rolled into a cylindrical shape before being placed in a protective case.
The chemical reaction also gives these capacitors a polarity that should be carefully observed. They can explode if the rated voltage is exceeded or the polarity is reversed, therefore do not connect an AC source to an electrolytic cap.
Don’t try this at home, but if you hook an aluminum electrolytic cap to a 120 VAC source, it will explode. Of course, if you do this and injure yourself I take no responsibility.
Both aluminum and tantalum electrolytic capacitors will be marked with either a “+” or a “-“ to indicate which plate is which.
These capacitors are popular due to their low cost and ability to provide a relatively high capacitance in a small package.
Aluminum electrolytics also leak badly, have bad tolerances, and have a high inductance. Because of this, they are good for low frequency applications and not so good for high frequency ones.
They should also not be used if the DC potential is well below the capacitor’s rated voltage.
These capacitors also have a limited life, even if they’re just sitting in your parts bin. When grabbing one that’s more than a few years old, be sure to check to see if it’s still in spec.
Typical values range from 0.1 µF to 500,000 µF or more.
Applications include power supply ripple filters, audio coupling, and bypassing.
A typical aluminum electrolytic capacitor appears in figure 6.
Figure 6: an aluminum electrolytic capacitor. Notice the stripe on the side that marks the negative plate.
Tantalum electrolytic capacitors are made with tantalum pentoxide and are polarized like their aluminum cousins.
They’re also smaller and more stable. They leak less and have less inductance than aluminum electrolytics. They sport a longer lifespan. The downside is that they’re more expensive and have a lower maximum voltage and capacitance.
Like aluminum electrolytics, tantalum caps can explode and/or burst into flames if the polarity reverses.
They often take up residence in analog signal systems that lack high current spike noise (spikes can damage them). Other applications include blocking, bypassing, decoupling, and filtering.
Tantalum caps are not good for high frequency applications. Like the aluminum versions, they should not be used if the DC potential is far below the rated voltage.
Figure 7 depicts a tantalum capacitor. Notice that they look different than the aluminum versions.
Figure 7: a tantalum capacitor. Notice the + sign which marks the positive lead.
Plastic Film Capacitors
These types of capacitors have replaced paper capacitors, which we will not discuss since they’re obsolete.
There are a few varieties of plastic film caps that are common, including polyester film and polypropylene film.
Polyester film capacitors (a.k.a. Mylar capacitors) use a thin polyester film as their dielectric (as any logical person may guess). Their tolerance (typically 5-10 percent) is not as good as polypropylene capacitors but they have good temperature stability and are cheap.
Polyester film caps are good for coupling and storage purposes. They often find use in audio and oscillator circuits and moderately high frequency circuits.
Capacitance values range from 0.001 µF to 10 µF.
Voltage ratings range from 50 V to 600 V.
Figure 8: a typical polyester film (Mylar) capacitor.
Polypropylene film capacitors have a higher tolerance than polyester film caps, so use them in place of polyester for applications that require a tighter tolerance.
Like polyester, they’re good for coupling and storage purposes, but also come in handy for noise suppression, blocking, bypassing, filtering, and timing.
Capacitance values range from 0.001 µF to about 0.47 µF.
Voltage ratings range from 100 V to 600 V.
Figure 9: a polypropylene film capacitor. Notice the similarity in appearance to the polyester film version.
Polystyrene capacitors aren’t film capacitors, but I lumped them here anyway.
These have a high inductance so they’re not good for high frequency applications. Exposure to temperatures above 160⁰ F (about 70⁰ C) will permanently damage them. Polystyrene is similar to Styrofoam (there is a slight difference; Styrofoam is a brand name, hence the capitalization), and Styrofoam melts. So does polystyrene.
Due to the high inductance, they are good for filtering and timing circuits running at a few hundred kilohertz or less. They’re also cheap with good stability.
Capacitance values range from 100 ρF to 0.027 µF.
Voltage ratings range from 30 V to 600 V.
Figure 10: various polystyrene capacitors.
Metalized Film Capacitors
Like the plastic film variety, these also come in both polyester and polypropylene. Since they both exhibit similar traits, we’re not going to treat them separately as we did with the plastic film caps.
Metalized film capacitors are made by using a vacuum deposition process that laminates a film substrate with an extremely thin (literally several atoms thick) aluminum coating.
They take up residence in circuits that use small signal levels (think low current and high impedance) where small physical size is a priority.
They’re not good for large signal AC applications.
One unique trait they possess is their self-healing ability. While shorts permanently destroy other capacitor types, these caps can heal themselves. Metalized film capacitors are also temperature stable with low drift.
You’ll find them in switching power supplies, audio circuits where sound quality is important, noise suppression circuit, snubbers and more.
Capacitance values range from 47 ρF to 22 µF, depending on the type.
Voltage ratings range from 63 V to 1250 V, again depending on the type.
Figure 11: various metalized film capacitors. I’m not sure what the dots on the side are for, but notice that they can look similar to their plastic film relatives.
Types of Capacitors – Wrapping it Up
Now we know something about the most common types of capacitors and what they’re good for and not good for.
Don’t forget to bookmark this post. It’ll come in handy.
Below is a nifty little chart that summarizes some of the characteristics of some of the capacitors we talked about.
We didn’t discuss it, but ESR stands for equivalent series resistance. ESR is a measure of the capacitor’s internal resistance and in series with it. Maybe ESR and other capacitor specs we didn’t discuss here will make an appearance in another article.
Figure 12: a quick run-down of several common capacitor types.
Until next time, comment and tell us: what types of capacitors do you use the most? Also, why do you pick that particular type?
- Cook, Nigel P. Introductory DC/AC Electronics, 4th Ed. Prentice Hall, 1999. Print.
- Scherz, Paul & Monk, Simon. Practical Electronics for Inventors, 4th Ed. McGraw Hill, 2016. Print.
- Byers, TJ. “Bypass Caps Demystified [the chart].” Nuts and Volts January 2007: 18-19. Print.