Voltage source

Source: Wikipedia, the free encyclopedia.
A schematic diagram of a voltage source, V, driving a resistor, R, and creating a current I

A voltage source is a two-

load resistance or the output current
. However, a real-world voltage source cannot supply unlimited current.

A voltage source is the

dual of a current source. Real-world sources of electrical energy, such as batteries and generators, can be modeled for analysis purposes as a combination of an ideal voltage source and additional combinations of impedance
elements.

Ideal voltage sources

An ideal voltage source is a two-terminal device that maintains a fixed

faults on electrical power systems
, the whole network of interconnected sources and transmission lines can be usefully replaced by an ideal (AC) voltage source and a single equivalent impedance.

Ideal Voltage Source Ideal Current Source
Controlled Voltage Source Controlled Current Source
Battery
of cells 		Single cell
Symbols used for sources

The

load resistance
, the current through the source approaches infinity as the load resistance approaches zero (a short circuit). Thus, an ideal voltage source can supply unlimited power.

If two ideal independent voltage source are directly connected in

parallel, they must have exactly the same voltage; Otherwise, it creates a fallacy
in logic, similar to writing down the equation .

Voltage sources in parallel shares the burden of current: If an exact duplicate of voltage is connected in parallel to the original one, either one of them will provide half of the electric current that the original voltage source would provide. For the remainder of the circuit, nothing has changed: These two voltage sources together provide the same voltage, and the same current as the original one alone.

No real voltage source is ideal; all have a non-zero effective internal resistance, and none can supply unlimited current. However, the internal resistance of a real voltage source is effectively modeled in linear circuit analysis by combining a non-zero resistance in series with an ideal voltage source (a Thévenin equivalent circuit).

Comparison between voltage and current sources

Most sources of electrical energy (the

battery
) are modeled as voltage sources. An ideal voltage source provides no energy when it is loaded by an
ohm output impedance in series with the source. A real-world voltage source has a very low, but non-zero internal resistance and output impedance
, often much less than 1 ohm.

Conversely, a

megohms
(at low frequencies) is typical.

Since no ideal sources of either variety exist (all real-world examples have finite and non-zero source impedance), any current source can be considered as a voltage source with the same

duals of each other and any non ideal source can be converted from one to the other by applying Norton's theorem or Thévenin's theorem
.

References and notes

  1. ^ An introduction to electronics
  2. ^ K. C. A. Smith, R. E. Alley , Electrical circuits: an introduction, Cambridge University Press, 1992
    ISBN 0-521-37769-2
    , pp. 11-13

See also
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