Ceramic Capacitor Working, Construction and Applications

The Capacitor is an electrical device that stores energy in the form of an electric field. It consists of two metal plates separated by a dielectric or non-conducting substance. The capacitor types broadly divided based on fixed capacitance and variable capacitance. The most important is the fixed capacitance capacitors, but capacitors with variable capacitance also exist. These include rotary or trimmer capacitors. Capacitors with fixed capacitance are divided into film capacitors, ceramic capacitors, electrolytic, and superconductor capacitors. Follow the link to know more Different types of capacitors. The ceramic capacitor described in more detail in this article.

Ceramic Capacitor Polarity and Symbol

Ceramic capacitors are most commonly found in every electrical device and it uses a ceramic material as the dielectric. The ceramic capacitor is a non-polarity device, which means they do no have polarities. So we can connect it in any direction on a circuit board.

For this reason, they are generally much safer than electrolytic capacitors. Here is the symbol for a non-polarised capacitor given below. Many types of capacitors, such as the tantalum bead do not have a polarity.

Construction and Properties of Ceramic Capacitors

Ceramic capacitors are available in three types, although other styles are available:

• Leaded disc ceramic capacitors for through-hole mounting which is resin coated.
• Surface mount Multi-Layer Ceramic Capacitors (MLCC).
• Special type microwave bare lead-less disc ceramic capacitors that are intended to sit in a slot on the PCB.

Ceramic disc capacitors are made by coating a ceramic disc with silver contacts on both sides as shown above illustrates. Ceramic disc capacitors have a capacitance value of about10pF to 100μF with a wide variety of voltage ratings, between 16V to 15 KV and more.

To gain higher capacitances, these devices can be made from multiple layers. The MLCCs are made with Paraelectric and Ferroelectric materials mix and alternatively layered with metal contacts.

After completion of the layering process, the device is brought to a high temperature and the mixture is sintered, resulting in a ceramic material of desired properties. Finally, the resulting capacitor consists of many smaller capacitors connected in parallel, this leads to an increase in capacitance.

The MLCCs consist of more than 500 layers, with the minimum layer thickness of approximately 0.5 microns. As technology progresses, the thickness of the layer decreases and capacitance increases in the same volume.

Ceramic capacitor dielectrics vary from one manufacturer to another, but common compounds include titanium dioxide, Strontium Titanate, and Barium Titanate.

Based on the working temperature range, temperature drift, tolerance different ceramic capacitor classes are defined.

Class 1 Ceramic Capacitors

Concerning temperature, these are the most stable capacitors. They have nearly linear characteristics.

The most common compounds used as the dielectrics are

• Magnesium Titanate for a positive temperature coefficient.
• Calcium Titanate for capacitors with a negative temperature coefficient.

Class 2 Ceramic Capacitors

Class 2 capacitors exhibit better performance for volumetric efficiency, but this is at the cost of lower accuracy and stability. As a result, they are normally used for decoupling, coupling and bypass applications where accuracy is not of prime importance.

• Temperature range: -50C to +85C
• Dissipation factor: 2.5%.
• Accuracy: average to poor

Class 3 Ceramic Capacitors

Class 3 ceramic capacitors offer high volumetric efficiency with poor accuracy and a low dissipation factor. It cannot withstand high voltages. The dielectric used is often Barium Titanate.

• Class 3 capacitor will change its capacitance by -22% to +50%
• Temperature range of +10C to +55C.
• Dissipation factor: 3 to 5%.
• It will have a fairly poor accuracy (commonly, 20%, or -20/+80%).

Class 3 type is typically used for decoupling or in other power supply applications where accuracy is not an issue.

Ceramic Disc Capacitor Values

Ceramic disc capacitor code normally consists of a three-digit number followed by a letter. It is very easy to decode to find the capacitor value.

The first two significant digits signify the first two digits of the actual capacitance value, which is 47 (the above capacitor).

The third digit is the multiplier (3), which is ×1000. The letter J implies the tolerance of ±5 %. Since this is the EIA coding system, the value will be in picofarads. Therefore, the value of the capacitor above is 47000 pF ±5 %.

For example, if a capacitor is marked as 484N, its value is 480000 pF ±30%.

Applications of Ceramic Capacitors

• Ceramic capacitors are majorly used in the resonant circuit in transmitter stations.
• Class 2 high-power capacitors are used in high voltage laser power supplies, power circuit breakers, induction furnaces, etc.
• Surface mount capacitors are often used in printed circuit boards and high-density applications.
• Ceramic capacitors can also be used as a general-purpose capacitor, because of their non-polarity and are available in a large variety of capacitances, voltage ratings, and sizes.
• Ceramic disc capacitors are used across brush DC motors to minimize RF noise.
• MLCC used in printed circuit boards (PCB) are rated for voltages from only a few volts up to several hundreds of volts, depending on the application.

From the above information finally, we can conclude that these capacitors employ Ceramic as the dielectric. Due to their non-polarity property, they can connect in any direction on a circuit board. We hope that you have got a better understanding of this concept. Furthermore, any doubts regarding this concept or to implement electronic engineering projects, please give your feedback by commenting in the comment section below. Here is a question for you, what are the different types of Ceramic Capacitor?