directcurrent

Direct current (DC) is an electric current that flows in a single direction, as opposed to alternating current (AC) which periodically reverses direction. In DC, the net flow of electric charges has a fixed polarity. In ideal DC, the magnitude is constant; real sources can exhibit ripple or noise.

DC is produced by sources such as chemical batteries, fuel cells, solar photovoltaic cells, and certain types of dynamo machines. Power supplies and chargers typically convert AC to DC through rectification and regulation. High-voltage direct current (HVDC) transmission is used for long-distance and submarine links, where it can reduce losses and improve controllability.

Voltage and current in DC are often characterized by a direct component, with any residual ripple superimposed on the level. DC voltages are usually described by their value and polarity.

Common applications include electronics and computers, where DC is required by transistors and integrated circuits; portable devices powered by batteries; low-voltage DC motor drives; and energy storage systems. Switching power supplies and DC-DC converters allow circuits to operate from various DC voltages.

Historically, direct current was promoted by Thomas Edison, but AC prevailed for general power transmission due to easier voltage transformation. Today, DC remains essential in modern electronics, renewable energy systems, and emerging DC grids, which integrate batteries, PV, and other sources.