Kuormapiiri

Kuormapiiri is the portion of an electrical circuit that consumes power from a source and performs useful work, such as lighting a lamp or driving a motor. In Finnish electrical engineering texts, kuormapiiri is contrasted with the source or drive circuitry, which supplies energy to the load.

Practically, a kuormapiiri is characterized by its impedance Z_L, which may be resistive, reactive, or nonlinear. In direct current (DC) circuits a simple resistive load is common; in alternating current (AC) circuits the load is described by a complex impedance with magnitude |Z_L| and phase angle φ. The current drawn from the source is I = V / Z_L, and the instantaneous power depends on the waveform and phase, with P = V_rms I_rms cos φ for AC when applicable.

Analysis and design treat the load as the terminal network connected to the source. Thevenin and Norton equivalents separate the energy source from the kuormapiiri so the response at the load can be studied. Impedance matching between source and load is important in many applications to maximize power transfer and maintain signal integrity; mismatches can cause reflections, losses, or instability in power electronics and RF systems.

Typical kuormapiirit include a light bulb, heater, electric motor, loudspeaker, or the input stage of a following circuit. Nonlinear or time-varying loads, such as rectifiers or switching regulators, may draw non-sinusoidal currents and change the effective impedance with time.

See also: load, impedance, Thevenin's theorem, maximum power transfer theorem.