# Electrical circuit

An electrical circuit is the combination of electrical or electromechanical individual elements (battery, switch, display, motor, ...) to form a functional arrangement. The circuit becomes usable by an electric current through its components ; this requires at least one electrical energy source contained in the circuit in a closed circuit .

An electrical circuit is shown schematically in the form of a circuit diagram or circuit diagram.

Simple circuit from a real power source (represented by its equivalent circuit diagram ) and a consumer (represented as a resistor)

## General considerations

### scope

An electrical circuit can consist of one or more circuits, in each of which certain sub-functions of the overall circuit are implemented. It can consist of the combination of just two bipolar elements, but also billions of elements in an integrated circuit .

### Electric sources

Like any other energy, electrical energy cannot be created or consumed, but is fundamentally obtained from another form of energy or released again in another form of energy. The terms source and consumer are still used and should be understood against this background.

As an element of the energy supply, a distinction is made in the circuits between the voltage source and its counterpart, the current source . In circuit theory, the terms are used for models of ideal sources. The simulation of their real behavior requires an equivalent circuit consisting of several idealized elements.

In terms of the application, one differentiates between a supplier of electrical energy (generator, solar cell, ...) and a generator of electrical signals (sensor, microphone, ...). When it comes to the supply of energy, a distinction is made between direct and alternating quantities with single-phase and three-phase alternating current , and when it comes to signal generation, analog or digital signals with which information can be transported.

### Electrical consumers

An electrical consumer is passive, such as an electrical resistor , a measuring device , an electrical device , an electrical system or an entire production facility in which electrical energy is converted into other forms of energy.

Losses occur with real sources and transmission paths, and the circuit is designed for voltage matching , current matching or power matching  - depending on whether the consumer is to be supplied with a maximum of electrical voltage , current or power .

For stationary processes, the current-voltage relationship of a consumer can often be specified linearly using Ohm's law or Ohm's law of alternating current technology . Semiconductor components generally behave non-linearly. In amplifier circuits , by negative feedback to ensure that their behavior is largely determined independently of the semiconductor parameters only by the properties of passive components so that the current-voltage relationship is linear then here.

### Cooperation

Mesh and knot:
The five components with the tensions up to form a closed circuit or a mesh. The points in between, at which more than two live lines meet, each form a node.${\ displaystyle U_ {1}}$${\ displaystyle U_ {5}}$

The components are connected to one another by electrical cables . Often they can be viewed as lossless. Otherwise, their line coverings like consumers in the circuit are to be observed.

The lines form meshes and knots for which the mesh and knot rules apply. Circuits with linear components and several sources can also be calculated according to the Helmholtz superposition principle .

## Special circuits

There are separate articles for a large number of circuits.