direct current

GC: n

CT: DC (direct current) is the unidirectional flow or movement of electric charge carriers (which are usually electrons). The intensity of the current can vary with time, but the general direction of movement stays the same at all times. As an adjective, the term DC is used in reference to voltage whose polarity never reverses.
In a DC circuit, electrons emerge from the negative, or minus, pole and move towards the positive, or plus, pole. Nevertheless, physicists define DC as traveling from plus to minus.
Direct current is produced by electrochemical and photovoltaic cells and batteries. In contrast, the electricity available from utility mains in most countries is AC (alternating current). Utility AC can be converted to DC by means of a power supply consisting of a transformer, a rectifier (which prevents the flow of current from reversing), and a filter (which eliminates current pulsations in the output of the rectifier).
Virtually all electronic and computer hardware needs DC to function. Most solid-state equipment requires between 1.5 and 13.5 volts. Current demands can range from practically zero for an electronic wristwatch to more than 100 amperes for a radio communications power amplifier. Equipment using vacuum tubes, such as a high-power radio or television broadcast transmitter or a CRT (cathode-ray tube) display, require from about 150 volts to several thousand volts DC.

S: (last access: 17 February 2015)

N: 1. direct (adj): late 14c., from Latin directus “straight,” past participle of dirigere “set straight”.
current (n): late 14c., from Middle French corant (Modern French courant), from Old French corant. Applied 1747 to the flow of electrical force.
d.c.: abbreviation of direct current, attested from 1898.
AC/DC (adj): electronics abbreviation of alternating current/direct current, by 1898. As slang for “bisexual,” 1959, said to have been in use orally from c.1940; the notion is of working both ways.
2. Electric current which flows in one direction only, as opposed to alternating current.
3. In most applications, direct current remains constant in value as well as direction, hence the French term “courant continu” is fully justified. However, there are cases where direct current varies significantly in value (as in “pulsating d.c.”), then “courant unidirectionnel” must be used as the French equivalent.

S: 1. OED – (last access: 17 February 2015). 2 & 3. TERMIUMPLUS.

SYN: dc, d.c., DC, D.C., continuous current (rare), unidirectional current.


CR: alternating current, electrical energy, electric current.