The
unidirectional flow of electric
charge particles is called Direct current or DC. That is the electric
current flows in a single direction. When a direct current is passed
through a conductor
the charge
across the area of cross-section is uniform. Direct current is usually
abbreviated as DC.
The value of
the Direct Current is always constant with respect to time and the below figure
shows its graphical representation. Hence in DC circuits the voltage and current
are independent on time.
 |
| Direct Current (DC) |
At the
initial stages of development of electrical systems DC is used being used as
means of transmission and distribution. Later with the adoption AC with its
capability of easy transformation DC system is rarely used.
Sources
of Direct Current:
Solar
cells: solar cells
or photo voltaic cells convert light energy into electrical
energy and they can only generate direct current.
DC
Generators: Though
DC generators generate DC but they do not generate pure DC instead they
generate pulsating voltages.
These have to be filtered with the help of filter circuits to get pure DC
Rectifiers: Rectifiers are the devices convert
AC to DC
Applications:
Electronics: Most of the electronic devices like
mobile phones, computers, radios, televisions, Audio/Video Players, LED lights,
electronic watches and calculators etc. work on DC. As the supplies system is
alternating current, these devices are powered with the help of rectifiers or
run over batteries.
HVDC: For bulk power transmission of
electric power over long distance High Voltage Direct Current (HVDC)
transmission is used. DC has advantage of less losses and no skin effect.
Electric
Vehicles: Electric
Vehicles are battery
powered vehicles which works on DC.
Rechargeable
Batteries: Rechargeable
batteries are energy storage devices which require DC input.