Direct Current (DC) Applications

Direct current or DC or continuous current is the constant flow of electrons in the single direction from low to high potential. This typically happens through a conductor like wire, or through semiconductors, insulators, or through a vacuum e.g. electron or ion beams. With DC the electric charges flow in the same direction.

The first commercial electric power transmission developed by Thomas Edison used direct current (D)C. Alternating current has transforming and transmission advantages over direct current, so it is used in today's electric power distribution. Applications needing direct current, have alternating current is distributed to a substation, and a rectifier is used to convert the power to direct current.

DC Applications

Direct current installations have different sockets, switches, and fixtures, because of the low voltages used. When using direct current reversing the polarity to a device isn't advisable unless the device has a diode bridge to correct it - most battery-powered devices don't. High voltage DC is used for long-distance point-to-point power transmission and for submarine cables.

DC is found in low-voltage applications powered by batteries which only produce DC, or solar power systems. Automotive applications generally use DC, but the alternator is an AC deviceusing a rectifier to produce DC. Most electronic circuits require a DC power supply. Applications needing fuel cells - mixing hydrogen and oxygen with a catalyst to produce electricity and water - produce only DC. Telephones connect to a twisted pair of internally separated wires - one is for the the AC voltage component (the audio signal), and one for the DC component used to power the phone.

Telephone exchange communication equipment e.g. DSLAM, uses standard -48V DC power supply and the negative polarity occurs by grounding the positive terminal of power supply system and the battery bank, thus preventing electrolysis depositions.