Direct current
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Direct current (DC or "continuous current") is the continuous flow of electricity 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).
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Direct current was used originally for electric power transmission after the development by Thomas Edison of the commercial generation of electricity in the late nineteenth century. It has mostly been abandoned for this purpose in favor of alternating current, see War of Currents, which is more convenient for electric power distribution and transmission. 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.
DC is commonly found in many low-voltage applications, especially where these are powered by batteries, which can only produce 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. 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.
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.) DC is also produced by arrays of solar cells used in solar power systems.
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).
See also
External links
- "AC/DC: What's the Difference (http://www.pbs.org/wgbh/amex/edison/sfeature/acdc.html)?". Edison's Miracle of Light, American Experience (http://www.pbs.org/wgbh/amex/index.html). (PBS)cs:Stejnosměrný proud
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