Capacitors are typically categorized by form factor, or the physical design, and the dielectric material used to store and release energy. Each type of capacitor offers unique characteristics that make each suitable for certain applications, environments, and products.Matthew Burris / CC BY 3.0 / Wikimedia Commons
Types of Capacitors
Capacitors are common components in an electronics lab and come in a variety of types. Each type of capacitor presents significant differences in typical and available values for capacitance tolerance, voltage rating, temperature stability, equivalent series resistance, size, and reliability. These differences influence how capacitors behave in the real world, making certain capacitors ideal for specific applications.
Common materials used for film capacitors include polyester (mylar), polystyrene, polypropylene polycarbonate, metalized paper, and Teflon. Film capacitors are available in values from a few picoFarads (pF) up to 100s of microFarads (uF). Some high-voltage film capacitors have voltage ratings exceeding 500 volts. The major advantage of film capacitors, especially those that use plastic films, is their long life and stable capacitance values.
Film capacitors are available in several package sizes and form factors. The most common form factors for film capacitors are cylindrical, oval, round, and rectangular. Most form factors are available with axial and radial style leads.
Electrolytic capacitors have some of the highest capacitance values of any type of capacitor. These capacitors are constructed with thin metallic films and an electrolytic semi-liquid solution. The flexibility of these materials allows them to be rolled up, providing ample surface area to create a large capacitance. Since the electrolytic solution is conductive and used as the second electrode, a thin dielectric oxide layer is grown on the metallic film to prevent it from shorting.
Electrolytic capacitors come with some limitations due to their polarization and voltage ratings. A downside of electrolytic capacitors is that most are polarized, so care must be taken to ensure they are used correctly. Placing an electrolytic capacitor in backward can cause a small explosion with the potential to damage anything nearby. All polarized electrolytic capacitors mark the polarity with a negative sign indicating which pin must be kept at the lowest electrical potential. The voltage rating of most electrolytic capacitors is low and can be found with voltage ratings up to several hundred volts.
The two common types of electrolytic capacitors are aluminum electrolytic capacitors and tantalum capacitors. Tantalum capacitors differ from most electrolytic capacitors. These look more like ceramic capacitors, but unlike ceramic capacitors, these are polarized. However, tantalum capacitors are more resilient for reversed polarities than aluminum electrolytic capacitors. Tantalum capacitors are sometimes placed in series with both negative terminals connected to form a non-polarized tantalum capacitor. Tantalum capacitors are smaller than aluminum electrolytic capacitors and have lower leakage currents, making these a better choice for many signal blocking, by-passing, decoupling, filtering, and timing applications.
Ceramic capacitors are some of the most common capacitors used, especially in surface-mount applications. These are made by coating a ceramic disc or plate with a conductor and connecting several together. The ceramic used has a high dielectric constant, which lets ceramic capacitors have a relatively high capacitance value despite the small size.
Unlike an electrolytic capacitor, a ceramic capacitor isn't polarized. However, its capacitance goes through a non-linear shift as its temperature changes. For this reason, ceramic capacitors are often used as decoupling or bypass capacitors. Ceramic capacitors are available in values ranging from a few pF to several uF and have voltage ratings from a few volts to tens of thousands of volts.
Other Types of Capacitors
Several specialty types of capacitors are available for specialized applications. For example, trimmer or variable capacitors offer adjustable capacitance and are useful for fine-tuning or compensation in the circuit. Ultracapacitors, on the other hand, are capacitors with high capacitance values, typically greater than one farad. These are often low-voltage and store enough energy to replace batteries in certain applications.