CAPACITORS
I. Definition:
A capacitor is a passive two-terminal electrical component that
stores potential energy in an electric field.
The effect of a capacitor is known as capacitance.
The capacitor was originally known as
a condenser or condensator.
Electrons accumulate on one plate forcing electrons away from
the other plate leaving a net positive charge
Think of a capacitor as very small, temporary storage of battery.
II. Composition:
A capacitor is formed from two conductors with equal and opposite surface charges +σ and −σ
separated by an insulating gap.
Conductor may be a foil, thin film, sintered bead of metal, or an electrolyte
The insulating gap is usually formed by non-conductor materials that is
called “dielectric” materials. The dielectric acts to increase the
capacitor's charge capacity. Materials commonly used as dielectrics
include glass, ceramic, plastic film, paper, mica, and oxide layers.
II. Properties:
A capacitor blocks the passage of Direct Current (DC).
A capacitor passes Alternating Current (AC)
The effect of capacitor is called capacitance with unit: Farads
(Michael Faraday). The capacitance of a capacitor is
proportional to the surface area of the plates (conductors) and
inversely related to the gap between them.
Working Voltage (WVDC)- The maximum continuous voltage which
can be safely applied to capacitor usually with values:
10V, 16V, 25V, 35V, 50V, 63V, 100V, 160V, 250V, 400V and 1000V.
III. The most common kinds of capacitors are:
Ceramic capacitors have a ceramic dielectric.
Film and paper capacitors are named for their dielectrics.
Aluminum, tantalum and niobium electrolytic capacitors are named after the material used as
the anode and the construction of the cathode (electrolyte)
Polymer capacitors are aluminum, tantalum or niobium electrolytic capacitors with conductive
polymer as electrolyte
Supercapacitor is the family name for:
1. Double-layer capacitors were named for the physical phenomenon of
the Helmholtz double-layer
2. Pseudocapacitors were named for their ability to store electric energy electro-
chemically with reversible faradaic charge-transfer
3. Hybrid capacitors combine double-layer and pseudocapacitors to increase power
density
Silver mica, glass, silicon, air-gap and vacuum capacitors are named for their dielectric.
Polarized capacitor
One lead is positive and other is negative marked. Can be connected one way in the circuit.
Three basic type:
Electrolytic Capacitor- Uses an electrolyte (an ionic conducting liquid) as one of its plates
to achieve a larger capacitance per unit volume than other types.
Electrolytic capacitors use the high dielectric constant of the aluminium oxide
layer on the plate of the capacitor which averages between 7 and 8. This is greater than
other dielectrics such as Mylar which has a dielectric constant of 3 and mica of around 6
- 8.
Tantalum Capacitor- consists of a pellet of tantalum metal as an anode, covered by an
insulating oxide layer that forms the dielectric, surrounded by liquid or solid electrolyte as
a cathode. Because of its very thin and relatively high permittivity dielectric layer, the
tantalum capacitor distinguishes itself as capacitors having high capacitance per volume
(high volumetric efficiency) and lower weight.
Can Capacitor
Non-Polarized capacitors
Type of capacitor that has no implicit polarity. It can be connected either way in the circuit. Also
known as “Bipolar Capacitors”.
Types of dielectric used:
Paper Mica
Ceramic Polyester
Glass Mylar
Application
De-coupling, noise filter, power conditioning, resonance, timer, snubber, motor starters,
sensors, touch twitch, signal processing
Variable Capacitor
A capacitors whose capacitance may be intentionally and repeatedly changed mechanically or
electronically
Types of variable capacitor:
Trimmer Capacitor- is used in some applications that generally have no need to adjust
again after the initial adjustment. The trimmer capacitor has an adjustable structure
adding to general ceramic capacitor to adjust capacitance.
Gang Capacitor- a variable capacitor whose capacitance may be intentionally and
repeatedly changed mechanically or electronically.
Application:
Impedance matching for antenna, RF tuning circuits, Radios, High powered transmitter
IV. How To Read:
CAPACITORS
GROUP 1:
ADARLO, Jewel Nerry A.
TABERNILLA, Danica Mae B.
VALDEZ, Russell G.
BSIE IV-GK
