Inductor application characteristics

inductance

The figure below shows the equivalent circuit of a real inductor. In this model, L represents the ideal inductance of the component. RW is the series resistance caused by the winding material and the terminals, while RI is the parallel resistance that accounts for hysteresis losses. C stands for the inherent capacitance between the windings. Understanding these parameters is essential when designing or selecting an inductor for a specific application. To minimize the inherent capacitance (C), inductors are typically not wound directly on the core. This is because the core’s high dielectric constant can significantly increase the capacitance, especially if the windings come into direct contact with it. Using a bobbin to separate the windings from the core helps reduce this effect. Additionally, the winding method plays a key role in controlling the capacitance: single-layer windings tend to have the lowest capacitance, while multi-layer windings can further reduce it through irregular patterns or by using multi-section bobbins. When aiming for a larger inductance value (L), magnetic cores with high permeability are often used. However, these materials also introduce hysteresis loss (RI) and may exhibit saturation at high current levels. Saturation occurs when the magnetic field becomes too strong, causing the inductance (L) to drop. Therefore, it's important to choose the right core material based on the circuit's requirements. Commonly used core materials include manganese-zinc ferrite, nickel-zinc ferrite, and iron powder. Manganese-zinc ferrite offers high permeability but has increased losses at higher frequencies. Nickel-zinc ferrite has lower permeability but performs better at high frequencies. Iron powder cores have moderate permeability (around 30–100) and are known for their resistance to saturation, making them suitable for applications where stability under high currents is crucial.