Technical Terms

The equivalent circuit is another circuit whose terminal current, voltage, and frequency characteristics are equal to those of the original circuit. The equivalent circuit simplifies a complex device's internal elements, representing the characteristics of a substitute circuit.

For example, a circuit with a DC motor is modeled using the equivalent circuit with resistance, inductance, mechanical elements to friction, etc. Thus, you can obtain information on the voltage/current characteristics similar to those of the motor.
Using an LCR meter that measures Inductance (l), Capacitance (C), and Resistance (R), all the parameters of the equivalent circuit model can be calculated in a "series" or "parallel" circuit" depending upon capacitance, inductance, or resistance.

The equivalent circuit helps secure better solutions to your measurement application by simplifying complex objects under certain conditions to make it easier to observe phenomena.
The equivalent circuit can also simulate things that are not electric circuits, such as mechanical vibrations. Therefore, it is available in various analysis fields, including impedance models of living organisms.

Series equivalent circuit
Series equivalent circuit | Technical Terms: Power Supplies | Matsusada Precision
Parallel equivalent circuit
Parallel equivalent circuit | Technical Terms: Power Supplies | Matsusada Precision