Capacitors from Wurth Electronics Midcom

At Wurth Electronics Midcom, we carry a variety of capacitors to suit your design needs. Read on to learn all about capacitors, including the different types of capacitors, popular capacitor products from Wurth Electronics Midcom, our special ABC of Capacitors design guide, and upcoming webinars on capacitors.

What Are Capacitors?

Capacitors are indispensable components in today’s electronics industry. Around two-thirds of the entire passive component market volume is attributed to capacitors.

So what exactly is a capacitor? We cover the basics below.

Technical Basics of Capacitors

The journey into the world of capacitors begins with the structure of the atom. A capacitor describes every arrangement for storing stationary electric charges.

The structure of a capacitor always consists of two conducting surfaces: the electrodes (sometimes referred to as sheets). They are always separated by an insulating material: the dielectric. You can see the relationship between the electrodes (1), the dielectric material (2), and the distance between electrodes (3) in the image provided.

These are the three key parameters used to distinguish the power and manipulate the performance of a capacitor.

The capacitance of a capacitor describes its capacity to store electric charges. It is calculated from the field constant, the relative permittivity of the dielectric used, the effective area (the overlapping area of the electrodes), and the thickness of the dielectric or the separation produced between the electrodes.

As an electronic component, a capacitor is able to store electrical energy and then release it again. This energy release takes place at a defined rate over a certain period depending on its design characteristics.

A capacitor is thus an energy reservoir, which blocks the direct flow of current with DC voltage and allows the flow of current with AC or pulsating voltage depending on its capacitance and the given frequency. That means the capacitor can assume a different role depending on the circuit:

  • In a DC circuit, it is a charge storage device.
  • In an AC circuit, it is a frequency-dependent resistor.

Essential Characteristics of Capacitors

  • The characteristics of of a capacitor are crucial in selecting one for a certain application. Here are the essential characteristics:
  • Capacitance
  • Equivalent circuit and its parameters
  • Rated voltage
  • Maximum continuous voltage
  • Insulation resistance
  • Residual current (DC leakage current)
  • Self-discharge
  • Dissipation factor and quality factor
  • Dielectric strength/voltage
  • Temperature coefficient/temperature dependence
  • Pulse rise time
  • Pulse loading capacity
  • Dielectric absorption
  • Ripple current
  • Complex permittivity

And that’s just the beginning! To get a solid understanding of capacitor characteristics and how they influence different applications, see our ABC of Capacitors design guide.

The Future of Capacitors

The future development of capacitors includes two essential approaches.

The first is to advance miniaturization in order to keep up with increasing integration density in the electronics industry.

The second is, of course, to increase capacitance. Since the capacitor (like the classical rechargeable battery) is a potential energy storage device, this is becoming increasingly attractive as the technology advances.

Types of Capacitors

There are several different types and constructions of capacitors. Capacitors with fixed capacitance are most common in modern electronics, though capacitors with variable capacitance (such as rotary or trimmer capacitors) do exist. Still, they play a rather subordinate role.

Capacitors with fixed capacitance can be distinguished by their polarity. A non-polar capacitor (film and ceramic) can be operated with both DC and AC voltage, while a polar capacitor (electrolytic and super) can be operated with DC voltage only.

The three main types of capacitors with fixed capacitance are film, ceramic, and electrolytic. We will describe each briefly below. For a more thorough overview of the different types of capacitors, check out our ABC of Capacitors design guide.

Film Capacitors

As mentioned, film capacitors have no polarity and a defined capacitance.

To construct a film capacitor, either 1) two metal films with an intermediate film, or 2) films of dielectric on which a metal layer is vapor deposited, are wound. Because of this, film capacitors are sometime called wound capacitors.

Film capacitors use either paper or plastic films for the dielectric material. Thus, types of film capacitors can be broken down based on the materials used (M = metalized; F = film; K = plastic; P = paper):

  • FP
  • FK
  • MP
  • MK

Because paper has several disadvantages (including low relative permittivity), plastic film capacitors (FK and MK) are generally preferred.

Ceramic Capacitors

Ceramic capacitors also have no polarity and a fixed capacitance, but they use ceramic materials for the dielectric material.

To construct a ceramic capacitor, either 1) a homogeneous block (single-layer capacitor), or 2) many layers (multilayer capacitor), give rise to a monolithic ceramic body. Single-layer ceramic capacitors are found in high-voltage and AC voltage applications, while multilayer ceramic capacitors (MLCCs) are mainly configured as SMD components. With quadrillions of units made, MLCCs are the predominating type in the world market.

The structure of ceramic capacitors enables very low inductance designs. The ceramics used as the dielectric can be divided into various classes:

  • Class 1 (low dielectric constant)
  • Class 2 (high dielectric constant)
  • Class 3
  • Class 4

Essentially, these classes differ in their relative permittivity, their dependency toward temperature, their aging behavior, and their dielectric losses. Classes 1 and 2 are more common; classes 3 and 4 (also called junction capacitors) are hardly of any importance today.

Bear in mind that ceramics are more sensitive to mechanical influences than other designs. This should be considered both in manufacturing and in the application itself.

Electrolytic Capacitors

Unlike the previous two types of capacitors, electrolytic capacitors do have polarity and only one metallic electrode. (There are non-polar or bipolar electrolytic capacitors, but they have much lower capacitance and are thus much less widespread.)

Because of the non-symmetrical structure of electrolytic capacitors, their electrodes can be distinguished as anode (a metal film, usually aluminum) and cathode (a conductive electrolyte).

Electrolytic capacitors can be distinguished based on two basic criteria: the electrode material (aluminum, tantalum, or niobium) and the property of the electrolytes (wet, solid, or a wet/solid hybrid).

The most common type of electrolytic capacitor is the aluminum electrolytic. There are essentially two types of aluminum electrolytic capacitors:

Electrolytic capacitors are available with connections for SMT, THT, snap-in, and screw versions. They are best used for high-capacitance applications that require excellent performance.

Popular Capacitors from Wurth Electronics Midcom

At Wurth Electronics Midcom, we carry a wide variety of capacitor products. There are two ways to view them: our online product catalog and our print product catalog. To access the print version, please contact your local sales representative for a copy.

Here is a brief overview of our capacitor product categories:

If you’re interested in trying any of our capacitors from Wurth Electronics Midcom, note that we offer free samples and design kits with lifelong free refills. Plus, there are no minimum quantities for orders!

Learn more about our exceptional customer service at Wurth Electronics Midcom here.

ABC of Capacitors Design Guide

To learn more about capacitors, order our ABC of Capacitors design guide. It is full of highly useful information on the following topics:

  • Basic principles of capacitors
  • Capacitor characteristics
  • Capacitor types

You can read free extracts from the ABC of Capacitors here. Like what you read? Fill out this form to get your copy.