# DC voltage

A direct voltage is an electrical voltage , the instantaneous value of which does not change over a longer observation period. It has the same sign and the same amount at all times. In a broader sense, the term DC voltage is also used when the DC component has priority in a periodically changing voltage and when the voltage does not change polarity .

Internationally, the abbreviation for identification is DC for direct current which uses direct current means, but also for DC voltage is used (as well as AC for AC / AC ).

Circuit symbol according to for an ideal DC voltage source with the electrical voltage ${\ displaystyle U}$

## generation

Galvanic cells and solar cells are voltage sources that generate direct voltage . Furthermore, direct voltage can arise from a source with only a low load capacity, but which can be significant as an electrical signal , for example thermal voltage .

A voltage created by rectification and smoothing

The electrical voltage generated in power stations by electrical generators due to a rotary movement, on the other hand, is an alternating voltage. DC voltage can be generated from this by means of rectifiers . This primarily creates a mixed voltage , the mean value of which is referred to as DC voltage. With smoothing capacitors , alternatively with larger currents or with clocked power supply units with upstream coils , the superimposed alternating component can be reduced considerably, so that only a small residual ripple remains; at the same time, the direct component can be increased to almost the peak value of the original alternating voltage. The greater the capacitance of the capacitor or the inductance of the coil, the lower the peak-valley value of the superimposed alternating voltage. The associated voltage made available to a consumer can now be viewed as direct voltage. In particular when used in communication systems, only a very small residual ripple is allowed so as not to disturb the sensitive electronics. In audio technology , if the smoothing is insufficient, a mains hum can be heard.

Depending on the requirements, electronic voltage regulators can be used to further "smooth". High-quality voltage regulators are controlled with reference voltage sources (which in themselves are not very loadable) .

Furthermore, direct voltage arises, for example, through friction and the formation of thunderstorms ; but this cannot be used technically.

## Notation

The symbol for the physical quantity "electrical voltage" is this ; at risk of confusion with alternating or pulsating voltage a DC voltage is characterized by a horizontal line as an index to the symbols so  . The unit symbol V for volts should not be given a label. For a DC voltage of 12 V. ${\ displaystyle U}$${\ displaystyle \ textstyle U _ {-}}$

${\ displaystyle U _ {-} = \; 12 \; \ mathrm {V}}$

to write. If the dash cannot be used, the index DC, derived from the Anglo-Saxon language area, is used - for both current and voltage, i.e. here . The addition to the volt as a unit symbol or is not permitted even according to international standards. ${\ displaystyle U _ {\ text {DC}}}$${\ displaystyle \ mathrm {VDC}}$${\ displaystyle \ mathrm {V \; DC}}$

In certain contexts (preferably in the case of digital technology components ), direct voltages or the connections for them are also marked with

• ${\ displaystyle U _ {\ text {SS}}}$for reference potential or ground ⏊
• ${\ displaystyle U _ {\ text {CC}}}$or for positive voltage against ⏊${\ displaystyle U _ {\ text {DD}}}$
• ${\ displaystyle U _ {\ text {EE}}}$ for negative voltage against ⏊