Definition and Types of Capacitors
– An electronic device that stores electrical energy in an electric field
– Accumulates electric charges on two closely spaced surfaces
– Insulated from each other
– Passive electronic component with two terminals
– Adds capacitance to a circuit
– Capacitors vary widely in physical form and construction
– Most capacitors contain at least two electrical conductors
– Metallic plates or surfaces separated by a dielectric medium
– Conductors can be foil, thin film, sintered bead of metal, or electrolyte
– Dielectrics commonly used include glass, ceramic, plastic film, paper, mica, air, and oxide layers
Applications and Advancements of Capacitors
– Widely used in electrical circuits of common devices
– Block direct current while allowing alternating current to pass
– Smooth the output of power supplies in analog filter networks
– Tune radios to specific frequencies in resonant circuits
– Stabilize voltage and power flow in electric power transmission systems
– Paper capacitors were commonly used in the late 19th century
– Porcelain and mica capacitors were used in early wireless apparatus
– Electrolytic capacitors with aluminum electrodes were invented in 1896
– Solid electrolyte tantalum capacitors invented in the 1950s
– Development of plastic materials led to the use of polymer films in capacitors
History of Capacitors
– Capacitors were first created in the 1740s as Leyden jars
– Ewald Georg von Kleist and Pieter van Musschenbroek were early inventors
– Benjamin Franklin discovered charge stored on glass, not water
– Early capacitors were known as condensers
– Compact construction methods developed in the early 20th century
Theory of Operation and Circuit Equivalence
– Capacitance is the ability to store electric charge
– Capacitor consists of two conductors separated by a non-conductive region
– Dielectric material reduces the electric field and increases capacitance
– Capacitance is defined as the ratio of charge to voltage
– In the long-time limit, capacitor is an open circuit
– In the short-time limit, capacitor is a short circuit
– Short-time equivalence is a voltage source with the capacitor’s initial voltage
– Long-time equivalence is an open circuit with no current flow
Capacitor Characteristics and Analysis
– Parallel-plate capacitor model consists of two conducting plates separated by a gap
– Capacitance of a parallel plate capacitor scales with the linear dimension or volume
– Unevenly charged plates result in different voltages between the plates
– Interleaved capacitors combine multiple parallel connected capacitors
– Energy stored in a capacitor is equal to the work done in establishing the electric field
– Current through a capacitor is proportional to the voltage and the derivative of charge
– Impedance and frequency affect the behavior of capacitors in circuits
– Displacement current flows through a capacitor in response to a sinusoidal voltage source
– Laplace circuit analysis represents the impedance of a capacitor in the s-domain
– Capacitors in parallel have the same applied voltage and their capacitances add up
– Capacitors in series store instantaneous charge build-up equal to each other
– Non-ideal behavior of capacitors includes leakage current, parasitic effects, breakdown voltage, temperature dependence, and non-uniform behavior at different frequencies. Source: https://en.wikipedia.org/wiki/Capacitor
A capacitor is an electronic device that stores electrical energy in an electric field by accumulating electric charges on two closely spaced surfaces that are insulated from each other. It is a passive electronic component with two terminals.
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| Type | Passive |
|---|---|
| Invented | Ewald Georg von Kleist, Pieter van Musschenbroek 1745 (independently) |
| Electronic symbol | |
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The effect of a capacitor is known as capacitance. While some capacitance exists between any two electrical conductors in proximity in a circuit, a capacitor is a component designed to add capacitance to a circuit. The capacitor was originally known as the condenser, a term still encountered in a few compound names, such as the condenser microphone.
The physical form and construction of practical capacitors vary widely and many types of capacitor are in common use. 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. Materials commonly used as dielectrics include glass, ceramic, plastic film, paper, mica, air, and oxide layers. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy, although real-life capacitors do dissipate a small amount (see Non-ideal behavior). When an electric potential difference (a voltage) is applied across the terminals of a capacitor, for example when a capacitor is connected across a battery, 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.
The earliest forms of capacitors were created in the 1740s, when European experimenters discovered that electric charge could be stored in water-filled glass jars that came to be known as Leyden jars. Today, capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass. In analog filter networks, they smooth the output of power supplies. In resonant circuits they tune radios to particular frequencies. In electric power transmission systems, they stabilize voltage and power flow. The property of energy storage in capacitors was exploited as dynamic memory in early digital computers, and still is in modern DRAM.
