How To Select a Capacitor

When I was working on the capacitors section for the next version of Common Parts Library, I realized that it would be helpful to explain why one might pick one capacitor type over another. This information is important because there are a lot of factors (temperature characteristics, package, etc.) which might make a type of capacitor (electrolytic or ceramic) better than others for your project.

In this blog, we will explain all the different types of capacitors, their merits and demerits, and popular applications. We have included some recommendations for commonly used capacitor series with high supply chain availability from Common Parts Library and Seeed Studio’s Open Parts Library and linked to pre-created searches on Octopart, such as the following for 50V rated Panasonic’s ECA-1HM series for 10µF to 3300µF:

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This is the first of a series of guides for passive selection: a deep-dive into selecting the correct capacitor for your project. Let’s dive into the world of capacitors:

Capacitors  capacitors2ceramiccapacitor tantalum

Capacitors are two-terminal components used for filtering, energy storage, voltage spike suppression, and many other applications. In their simplest form, they consist of two parallel plates separated by an insulating material called a dielectric. Capacitors store electrical charge. The unit of capacitance is Farad (F), attributed to Michael Faraday who was a pioneer in using capacitors for practical applications.

Capacitors can either be polarized or non-polarized. Polarized capacitors — nearly all electrolytic and tantalum capacitors — can only be connected one way in a circuit: if the “-” terminal goes above “+” terminal, it could lead to a short. Non-polarized capacitors — ceramic, mica, and film capacitors — can be connected either way in a circuit, so they are suitable for AC.

Even though capacitors are so commonly used, it can be tricky to select one for your project. While you might know what capacitance or voltage rating your project requires, capacitors have lots of other characteristics — such as polarization, temperature coefficient, stability, equivalent series resistance (ESR) and so on — that might make them a great (or poor) choice for your project. The most popular types of capacitors are presented below with this in mind.


TYPES
There are several different types of capacitors which differ by polarity, performance and cost. Below are some of the common capacitor types: aluminum electrolytic, ceramic, tantalum, film, mica and polymer capacitors, along with their characteristics, applications, package information as well as info on part selection.

I. Aluminium Electrolytic Capacitors capacitors3

Characteristic: Aluminum Electrolytic Capacitors are polarized, so they cannot be used with AC. They can achieve high capacitance value but with large variations, typically 20%.

Applications: These are useful in applications which do not need tight tolerances or AC polarization. They are most commonly used in power supplies for decoupling purposes, i.e. to reduce voltage ripple reaching the circuit. They are also used widely in DC/DC switching voltage converters.

Package: Available in through-hole as well as surface mount package.

Part Selection:
Through-Hole: 6.3V rated Panasonic’s ECA-0JM series for 220µF to 22000µF.  
                          50V rated Panasonic’s ECA-1HM series for 10µF to 3300µF.
                          
Surface Mount:
 6.3V rated Panasonic’s EEE-HD0J series for 330µF to 1000µF.
                           50V rated Panasonic’s EEE-HD1H series for 1µF to 100µF.

II. Ceramic Capacitorsceramiccapacitor

Characteristic: There are two main types of ceramic capacitors: Multi-layer chip capacitors (MLCCs) and ceramic disc capacitors. MLCCs are very widely used in electronic devices and are popular because they have high stability and low losses. They have lower Equivalent Series Resistance (ESR) and variation compared to electrolytic or tantalum capacitors but can achieve lower capacitance (only up to a few µF) . Because of high packing densities, MLCC capacitors provide a size advantage and are great for printed circuit boards (PCBs).

Applications: Since these are not polarized, they can be be used with AC. They are widely used as a ‘general-purpose’ capacitor and used for high frequency blocking, filtering, oscillator tuning and EMI suppression.

Both MLCCs and ceramic disc capacitors are further divided into two application classes:
Class I ceramic capacitors are accurate (+/- 5%) and temperature-compensated- they have very low change of capacitance with temperature. NP0/C0G are popular, and have a tolerance of 30ppm/K, but are available only up to the nanoFarad (nF) range. Because they are very stable and accurate, they are used in frequency control applications such as resonant circuits for radio applications.
Class II ceramic capacitors are less accurate but provide higher volumetric density (up to µF range) and hence suitable for smoothing or decoupling applications.  Also, they have a large voltage coefficient – a 50% decrease in capacitance value at half the maximum VDC is common.
X5R: Can operate from -55C to 85C with variation of +/- 15%
X7R: Can operate from -55C to 125C with variation of +/- 15%
Y5V: Can operate from -30C to 85C with variation of +22/-82%

Package: 0201, 0402, 0603, 0805, 1206 and 1812 packages are most common. The numbers represent the dimensions in imperial system, with 0402 being 0.04 X 0.02 inches and 0603 being 0.06 X 0.03 inches and so on.

Part Selection:
NP0/C0G type: 0402 Yageo’s CC0402JRNPO9 series for 10pF to 1nF
                           0603 Yageo’s CC0603JRNPO9 series for 8pF to 2.7nF

X7R type:   0402 Yageo’s CC0402KRX7R9BB series for 100pF to 10nF
                   0603 Yageo’s CC0603KRX7R9BB series for 100pF to 100nF
                   0603 Yageo’s CC0603KRX7R7BB series for 100nF to 1µF

Through-Hole type: Kemet’s C315C series for 1pF to 1µF

III. Tantalum Capacitors tantalum

Characteristic: These are a subtype of electrolytic capacitors and are highly polarized.  Care needs to be taken as they are known to have catastrophic failure modes which can be triggered by voltage spikes even slightly more than rated voltage. They can achieve high capacitance value and are very stable over time. They are smaller in size than aluminum electrolytic capacitors of the same capacitance but can handle lower maximum voltages.

Applications: Due to their low leakage current, stability, and high capacity, they are common for sample and hold circuits which rely on low leakage current to achieve long hold duration. They are also used in power supply filtering due to their smaller size and long term stability.

Package: Available in through-hole as well as surface mount (SMD) packages but SMD packages are more popular. In imperial system:
Series A corresponds to size 1206 (this corresponds to dimensions 0.12 X 0.06 inches)
Series B corresponds to size 1210
Series C corresponds to size 2312
Series D corresponds to size 2917

Part Selection:
Series A: AVX’s TAJA series for 1µF to 10µF
Series B: AVX’s TAJB series for 10µF to 47µF
Series C: AVX’s TAJC series for 47µF to 220µF
Series D: AVX’s TAJD series for 220µF to 680µF

IV. Film Capacitors  filmcapacitors

Film capacitors are non-polarized which makes them suitable for AC signal use. They have low Equivalent Series Resistance (ESR) and self-inductance (ESL) and are used in A/D converters.  They can handle high peak current and can thus be used as snubber capacitors to “snub” inductive kickback voltage spikes in DC-DC converters.

Part Selection: TDK’s B32 series for 1nF to 10µF

V. Mica Capacitors micacapacitors

Mica capacitors are non-polarized, have low losses, high stability, and have great high-frequency properties. They are useful for radio frequency circuits. Mica capacitors can cost a few dollars per piece, so they are being replaced by ceramic capacitors for low-power applications. However, they remain critical for high power applications such as RF transmitters due to their high breakdown voltage.

Part Selection: CDE’s MC series for 1pF to 1nF (SMD) and
                         CDE’s CD series for 1pF to 10nF (Through-Hole)

VI. Polymer Capacitors polymercapacitors

Polymer capacitors are polarized just like other electrolytic capacitors but have several advantages such as lower losses due to lower ESR and longer lifetime. For conventional aluminium electrolytic capacitors, there is a risk of electrolyte dry-out at lower temperatures, but due to the use of solid polymer material as dielectric, polymer capacitors have high reliability even at very low temperatures.

Polymer capacitors are used in place of electrolytic capacitors for high quality motherboards and DC-DC converters.

Part Selection: Panasonic’s OS-CON series for 3.3µF to 2700µF

This guide covers some of the most popular types of capacitors. Apart from these, there are supercapacitors, silicon capacitors, niobium oxide capacitors, and trimmer capacitors which all have unique advantages in either capacity, reliability or tuning ability. However, in most electronic projects you are likely to see one of the six types that we have discussed in this guide. If you have any comments or suggestions on the part selection, drop us a note in our Slack chat room or in comments below. A guide on how to select resistors and inductors is coming next. Stay tuned!

Update: March 23, 2016 4:48 PM – this article has been edited to include contributions from users online.

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  • Allen Moore

    Low ESR and ESL are mentioned several times in the article. What is the importance of these specs? In what type of designs would these specs need to be considered?

    • Sanket Gupta

      Thanks for the question!
      Low ESR and ESL mean there are lower losses. When current passes through ESR, there is a voltage drop and heat is released due to resistive element, thus reducing the durability of the capacitor. In general, capacitors with lower ESR have longer lifetime.
      If capacitors are used with LDOs for external compensation, their ESRs can potentially cause instability leading to ringing/oscillations. This note from TI explains further: http://www.ti.com/lit/an/slyt187/slyt187.pdf

      ESL affects the ripple voltage, and it needs to be ensured that the resonant frequency is further away than the frequency of operation. This becomes critical in high speed ADCs and in RF applications.

  • russnelson

    There are also tuner capacitors, for completion’s sake. I don’t know of anybody putting them into new designs.

  • dichasium

    I had hoped to have a go at repairing my Panasonic breadmaker but can’t find it’s capacitor anywhere. Anyone know how to get 1 or 2 of these : f 47ufk 250vac ? Thanks, Karen