Capacitors

We offer a vast array of capacitors to suit a wide variety of applications. Here is some information about capacitor types, how they work, how to choose them, and applications.

A capacitor is a device that stores electrical energy in an electric field by accumulating electric charges on two surfaces insulated from each other but in close proximity. It is a passive electronic component with two terminals.

How does a capacitor work?

Most capacitors contain at least two electrical conductors, often in the form of metallic plates or surfaces separated by a dielectric medium. A conductor may be a foil, thin film, sintered bead of metal, or an electrolyte. The nonconducting dielectric acts to increase the capacitor's charge capacity.

When a voltage is applied across the terminals of a capacitor, an electric field develops across the dielectric, causing a net positive charge to collect on one plate and net negative charge to collect on the other plate. No current actually flows through the dielectric. However, there is a flow of charge through the source circuit. If the condition is maintained sufficiently long, the current through the source circuit ceases. If a time-varying voltage is applied across the leads of the capacitor, the source experiences an ongoing current due to the charging and discharging cycles of the capacitor.

Types of capacitors:

Ceramic: A ceramic capacitor is one of the most commonly used forms. The material used in this capacitor type is dielectric. Ceramic capacitors are non-polar devices.

Ceramic capacitors are classified into three groups:

1. Leaded disc ceramic capacitors
2. Surface mount multi-layered ceramic capacitors
3. Microwave bare lead-less disc ceramic capacitors

Film capacitors: Film capacitors are also known as a polymer film, plastic film, or film dielectric. The advantage of film capacitors is that they are inexpensive and have limitless shelf life. The general voltage range of these capacitors is from 50V to 2kV.

Power Film Capacitors: Construction techniques and materials that are used in power film capacitors are similar to those of ordinary film capacitors. Polypropylene film is used as a dielectric.

Electrolytic Capacitors: In an electrolytic capacitor a metallic anode is coated with an oxidized layer used as a dielectric. These capacitors are polarized. Electrolytic capacitors are categorized based on their dielectric:

1. Aluminium electrolytic capacitors – aluminium oxide (dielectric).
2. Tantalum electrolytic capacitors – tantalum pentoxide (dielectric).
3. Niobium electrolytic capacitors – niobium pentoxide (dielectric).

Paper Capacitors use paper as the dielectric material. The amount of electric charge stored by the paper capacitor is fixed. It consists of two metallic plates, and the paper dielectric which is placed between these plates.

How to choose a capacitor

When deciding on capacitor types there are a handful of factors to consider:

1. Size - Size both in terms of physical volume and capacitance.
2. Maximum voltage - Each capacitor is rated for a maximum voltage that can be dropped across it.
3. Leakage current - Capacitors aren't perfect. Every capacitor is prone to leaking some tiny amount of current through the dielectric, from one terminal to the other. Leakage causes energy stored in the capacitor to slowly, but surely drain away.
4. Equivalent series resistance (ESR) - The terminals of a capacitor always have a small but measurable resistance – usually below 0.01Ω. This will produce heat and power loss at larger currents.
5. Tolerance - Capacitors also can't be made to have an exact, precise capacitance. Each cap will be rated for their nominal capacitance, but, depending on the type, the exact value might vary anywhere from ±1% to ±20% of the desired value.

Applications for capacitors

1. Energy storage
2. Power conditioning
3. Pulsed power
4. Power factor correction
5. Sensors
6. Coupling
7. Tuning
8. Decoupling
9. Suppression
10. High pass and low pass filters
11. Noise filters and snubbers