Energy storage
A capacitor can
store electric energy
when disconnected from
its charging circuit,
so it can
be used like
a temporary battery.
Pulsed power and
weapons
Groups of large, specially constructed, low-pulses of
current for many pulsed power applications. These include lasers (especially
TEA lasers), pulse forming networksLarge
capacitor banks(Reservoir) are
used as energy
sources for the detonators in nuclear weapons and other specialty
weapons. Experimental work is under way using banks of capacitors as power
sources for electromagnetic armor and electromagnetic
Power conditioning
Reservoir capacitors are used in power suppliesalso be used
in charge pump circuits as the energy
storage element in the generation of higher voltages than the input voltage
(such as stun gun). Capacitors are connected in parallel with the power
circuits of most electronic devices and larger
systems (such as
factories) to shunt
away and conceal
current fluctuations from the primary
power source to pacitor
can store electric
energy when disconnected
from its charging
circuit, so it can be
used like a
temporary . Capacitors are commonly used in electronic devices to maintain
power supply while batteries are being changed.
Power factor
correction
In electric power distribution, capacitors are used for
power factor correction.
Signal coupling
Because capacitors pass AC but block DC signals (when
charged up to the applied dc voltage), they are often used to separate the AC
and DC components of a signal. This method is known as AC coupling or
"capacitive coupling".
Decoupling
A decoupling capacitor is a capacitor used to decouple one
part of a circuit from another. Noise caused by other circuit elements is
shunted through the capacitor, reducing the effect they have on the rest of the
circuit. It is most commonly used between the power supply and ground. An
alternative name is bypass capacitor as it is used to bypass the power supply
or other high impedance component of a circuit.
Noise filters and
snubbers
When an inductive circuit is opened, the current through the
inductance collapses quickly, creating a large voltage across the open circuit
of the switch or relay. If the
inductance is large enough, the energy will generate a spark, causing the contact
points to oxidize, deteriorate, or sometimes weld together, or destroying a
solid-state switch. A snubber capacitor across the newly opened circuit creates
a path for this impulse to bypass the contact points, thereby preserving their
life; these were commonly found in contact breaker ignition systems, for
instance. Similarly, in smaller scale circuits, the spark may not
be enough to damage
the switch but
will still radiate
undesirable radio frequency interference
(RFI), which a filter capacitor
absorbs. Snubber capacitors are usually employed with a low-value resistor in
series, to dissipate energy and minimize RFI. Such resistor-capacitor
combinations are available in a single package.
Motor starters
In single phase squirrel cage motors, the primary winding
within the motor housing isn't capable of starting a rotational motion on the
rotor, but is capable of sustaining one. To start the motor, a secondary winding
is used in series with a non-polarized starting capacitor to introduce a lag in
the sinusoidal current through the starting winding. When the secondary winding
is placed at an angle with respect to the primary winding, a rotating electric
field is created. The force of the rotational field is not constant, but is
sufficient to start the rotor spinning.
Signal processing
The energy stored in a capacitor can be used to represent
information, either in binary form, as in DRAMs, or in analogue form, as in
analog sampled filters and CCDs. Capacitors can be used in analog circuits as
components of integrators or more complex filters and in negative feedback loop
stabilization. Signal processing circuits also use capacitors to integrate a
current signal.
Sensing
Most capacitors are designed to maintain a fixed physical
structure. However, various factors can change the structure of the capacitor;
the resulting change in capacitance can be used to sense those factors.
Changing the
dielectric:
The effects of varying the physical and/or electrical
characteristics of the dielectric can also be of use. Capacitors with an exposed
and porous dielectric can be used to measure humidity in air. Capacitors are
used to accurately measure the fuel level in airplanes; as the fuel covers more
of a pair of plates, the circuit capacitance increases.
Changing the
distance between the plates:
Capacitors with a flexible plate can be used to measure
strain or pressure. Industrial pressure transmitters used for process control
use pressure-sensing diagphragms, which form a capacitor plate of an oscillator
circuit. Capacitors are used as the sensor in condenser microphones, where one
plate is moved by air pressure, relative to the fixed position of the other plate.
Some accelerometers use MEMS capacitors etched on a chip to measure the magnitude
and direction of the acceleration vector. They are used to detect changes in
acceleration, eg. as tilt sensors or to detect free fall, as sensors triggering
airbag deployment, and in many other applications. Some fingerprint sensors use
capacitors. Additionally, a user can adjust the pitch of a theremin musical
instrument by moving his hand since this changes the effective capacitance between
the user's hand and the antenna.
Changing the
effective area of the plates:
Capacitive touch switches are now used on many consumer
electronic products.
