Electric circuit theory is often divided into special topics, either on the basis of how the voltages and currents in the circuit vary with time (direct-current, alternating-current, nonsinu-soidal, digital, and transient circuit theory) or by the arrangement or configuration of the electric current paths (series circuits, parallel circuits, series-parallel circuits, networks, coupled circuits, open circuits, and short circuits). Circuit theory can also be divided into special topics according to the physical devices forming the circuit, or the application and use of the circuit (power, communication, electronic, solid-state, integrated, computer, and control circuits).
The path taken by an electric current in flowing through a conductor through one complete run of a set of wires from a power source, such as a panelboard, to various electrical devices and back to the same power source. The wires used for various circuits are prescribed by codes, such as the National Electrical Code.
In design documentation, a document showing in conventional notation the components of an article or installation and the connections or links between components. Diagrams are usually drawn without regard to scale or to the actual spatial arrangement of the components. They may be classified according to the type of components and connections between components as electrical, pneumatic, hydraulic, kinematic, or combination diagrams. They may also be classified according to the purpose for which they will be used.
An important concept in electronic circuits is that of feedback. Feedback occurs when an output signal is fed around a device to contribute to the input of the device. Consequently, when positive feedback occurs, that is, when the output signal returns to reinforce itself upon being fed back, it can lead to the generation of signals which may or may not be wanted. Circuit designers need to be conscious of all possible feedback paths that are present in their circuits so that they can ensure that unwanted oscillations do not occur. In the case of negative feedback, that is, when the output signal returns to weaken itself, then a number of improvements in circuit performance often ensue; for example, the circuit can be made less sensitive to changes in the environment or element variations, and deleterious nonlinear effects can be minimized.