Component Models
Actual passive two-terminal components can be represented by some network of lumped and distributed ideal inductors, capacitors, and resistors, in the sense that the real component behaves as the network does. Some of the components of the equivalent circuit can vary with conditions, e.g., frequency and temperature.
If driven by a periodic sinewave (alternating current) the component will be characterised by its complex impedance Z(ω) = R + j X(ω); the impedance can involve several minor resistances, inductances and capacitances in addition to the main property. These small deviations from the ideal behavior of the device can become significant under certain conditions, typically high frequency, where the reactance of small capacitances and inductances can become a significant element of circuit operation. Models of lesser or greater complexity can be used, depending upon the accuracy required. For many purposes a simple model with an inductance or capacitance in series with an ESR is good enough.
These models, however simple or complex, can be inserted into a circuit to calculate performance. Computer tools are available for complex circuits; e.g., the SPICE program and its variants.
Pure capacitors and inductors do not dissipate energy; any process which dissipates energy must be treated as one or more resistors in the component model.
Read more about this topic: Equivalent Series Resistance
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