Direct current

Direct current (DC or "continuous current") is the continuous flow of electric charge through a conductor such as a wire from high to low potential. In direct current, the electric charges flow always in the same direction, which distinguishes it from alternating current (AC). A term formerly used for direct current was Galvanic current.

Related Topics:
Current - Electric charge - Potential - Alternating current - Term formerly used

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Historically, the first commercial electric power transmission (developed by Thomas Edison in the late nineteenth century) used direct current.

Related Topics:
Electric power transmission - Thomas Edison - Nineteenth century

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Because alternating current is more convenient than direct current for electric power distribution and transmission, today nearly all electric power transmission uses alternating current. See War of Currents.

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High voltage direct current is used for long-distance point-to-point power transmission and for submarine cables, with voltages from a few kilovolts to approximately one megavolt.

Related Topics:
High voltage direct current - Submarine cable

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DC is commonly found in many low-voltage applications, especially where these are powered by batteries, which can produce only DC, or solar power systems, since solar cells can produce only DC. Most automotive applications use DC, although the generator is an AC device which uses a rectifier to produce DC. Most electronic circuits require a DC power supply.

Related Topics:
Voltage - Batteries - Solar power - Solar cell - Generator - Rectifier - Electronic - Power supply

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Although DC stands for "Direct Current", DC is generically used to refer to constant polarity voltages. Some forms of DC vary wildly in voltage, such as the raw output of a rectifier. Running them through an RC low-pass filter will produce more stable voltage. Other forms of DC (such as that produced by a voltage regulator) have almost no variations in voltage (but may still have wild variations in output electric power and current).

Related Topics:
Voltage - Voltage regulator - Electric power

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Direct current installations usually have different types of sockets, switches, and fixtures, mostly due to the very low voltages used, from those suitable for alternating current. It is usually extremely important with a direct current appliance to not reverse polarity unless the device has a diode bridge to correct for this. (Most battery-powered devices don't.)

Related Topics:
Socket - Switch - Fixture - Diode bridge

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Within Electrical Engineering, the term DC is also a synonym for constant. For example, the voltage across a DC voltage source is constant as is the current through a DC current source. The DC solution of an electric circuit is that solution where all voltages and currents are constant. In this context, a voltage (current) that is changing with time cannot be a DC voltage (current) even if the polarity (direction) does not change. However, it can be shown that such a changing voltage or current can be decomposed into the sum of a DC component and an AC component. The DC component is defined to be the average value of the voltage or current over all time. The average value of the AC component is exactly zero as with, for example, a sine wave).

Related Topics:
Electrical Engineering - Voltage source - Current source - Electric circuit - Sine wave

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Most telephones connect to a twisted pair of wires, and internally separate the AC component of the voltage between the two wires (the audio signal) from the DC component of the voltage between the two wires (used to power the phone).

Related Topics:
Telephone - Twisted pair

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