capacitor

capacitor
Name	Capacitor
Caption	A typical fixed-value capacitor
Type	Passive
Invented	Ewald Georg von Kleist, Pieter van Musschenbroek (1745–1746)
First produced	18th century
Pin1	Anode / Positive
Pin2	Cathode / Negative

capacitor. A capacitor is a fundamental passive electronic component that stores electrical energy in an electric field. It is constructed from two conductive plates separated by an insulating material known as a dielectric. The device's ability to store charge, measured in farads, is essential for a vast array of functions in modern electrical and electronic systems, from filtering and timing to energy storage and power conditioning.

Overview

The basic principle of the capacitor was discovered independently in the mid-18th century by Ewald Georg von Kleist in Pomerania and by Pieter van Musschenbroek at the University of Leiden, who created the first recognizable device known as the Leyden jar. This early form consisted of a glass jar coated with metal foil, serving as a primitive but effective charge storage vessel. Modern capacitors are integral to virtually every electronic circuit, found in devices ranging from the smallest integrated circuit to massive installations in the power grid. Their physical forms vary widely, from tiny surface-mount chips to large cylindrical units used in power factor correction for industrial machinery.

Theory of operation

When a voltage is applied across the conductive plates, an electric field develops across the dielectric, causing positive charge to accumulate on one plate and negative charge on the other. This process, governed by the fundamental laws of electrostatics, continues until the potential difference between the plates equals the applied voltage. The amount of charge stored for a given voltage defines the capacitance, a property directly proportional to the surface area of the plates and the permittivity of the dielectric, and inversely proportional to the distance between them. The relationship between charge, voltage, and capacitance is described by the equation Q = CV, a cornerstone of circuit theory formalized by scientists like James Clerk Maxwell.

Types of capacitors

Capacitors are categorized primarily by their dielectric material and construction, which dictate their performance characteristics. Common fixed-value types include ceramic capacitors, which use a ceramic dielectric and are prevalent in high-frequency applications; electrolytic capacitors, which employ an oxide layer for high capacitance in power supplies; and film capacitors, which use a plastic film and are valued for stability. Specialized varieties include tantalum capacitors, known for high density and reliability in military and aerospace applications, and supercapacitors, which use electrochemical principles for extremely high energy storage. Variable capacitors, whose capacitance can be adjusted mechanically, were historically crucial in tuning radio receivers.

Applications

Capacitors serve critical roles across all fields of electrical engineering. In analog circuits, they are used for filtering signals, such as in the crossover networks of loudspeaker systems designed by companies like Bose Corporation. In digital electronics, they provide local energy storage to stabilize power supply voltages for microprocessors from manufacturers like Intel. Within power systems, they are employed for power factor correction to improve efficiency, a practice standardized by organizations like the Institute of Electrical and Electronics Engineers. They are also essential in timing circuits, such as those in the 555 timer IC, and in energy storage applications like the flash units in cameras from Nikon.

Characteristics and parameters

Key specifications beyond basic capacitance include the voltage rating, which indicates the maximum safe operating voltage before dielectric breakdown, and the equivalent series resistance, a measure of internal losses that affects performance at high frequencies. The temperature coefficient describes how capacitance varies with temperature, a critical factor for components used in environments like those encountered by the NASA Mars Rover. Other important parameters are the dissipation factor, which indicates energy loss, and the insulation resistance, which measures leakage current. Standards for these parameters are often set by international bodies such as the International Electrotechnical Commission.

History and development

Following the invention of the Leyden jar, capacitors were fundamental to early experiments in electricity conducted by figures like Benjamin Franklin and Alessandro Volta. The 19th century saw theoretical advances through the work of Michael Faraday, who conducted extensive research on dielectrics and for whom the unit of capacitance is named. The dawn of wireless telegraphy and radio in the early 20th century, pioneered by Guglielmo Marconi, drove demand for more reliable and compact capacitors. The post-World War II electronics revolution, fueled by the invention of the transistor at Bell Labs, necessitated the development of miniature capacitors compatible with printed circuit board technology, leading to the diverse and highly specialized components used globally today.

Category:Electronic components Category:Electrical components Category:Energy storage