Series Inductance Calculator

Series inductors add directly: L_total = L1 + L2 + L3 + ... when there is no magnetic coupling between them. This is the simplest inductor configuration and mirrors series resistors in its direct addition rule. The total inductance determines the combined energy storage, impedance, and filtering characteristics of the series inductor network.

However, when inductors are physically close, their magnetic fields interact through mutual inductance (M). For two coupled inductors in series, the total inductance is: L_total = L1 + L2 ± 2M. The plus sign applies when the inductors are wound to aid each other (current enters both at dotted terminals), increasing total inductance. The minus sign applies when they oppose each other, decreasing total inductance. This mutual coupling effect is the principle behind coupled inductors, transformers, and common-mode chokes.

Series inductors are used extensively in filtering applications. A series inductor in a power supply filter presents high impedance to AC ripple while passing DC load current with minimal voltage drop (limited only by the wire's DC resistance, DCR). Multiple series inductors create a cascaded filter for higher ripple attenuation. The series impedance XL = 2πfL increases with frequency, providing better filtering at higher harmonic frequencies.

In RF circuit design, series inductors form part of impedance matching networks. An L-network for matching a 50 Ω source to a high-impedance antenna typically uses a series inductor and a shunt capacitor. The series inductor value is chosen for proper impedance transformation at the target frequency.

Common-mode chokes are a practical application of magnetically coupled series inductors. Two coils wound on the same ferrite toroid core are connected in series with the supply and return conductors. For differential (normal) current, the fluxes cancel (opposing configuration), giving very low impedance. For common-mode noise, the fluxes add (aiding configuration), giving high impedance that suppresses EMI. The mutual inductance M equals nearly L1 = L2 for a tightly coupled common-mode choke, making differential impedance ≈ 0 while common-mode impedance = 2L.

This calculator provides both the uncoupled series inductance (L1 + L2 + L3) and the two-inductor coupled inductance (L1 + L2 ± 2M), along with inductive reactance at the specified frequency — a complete toolkit for inductor network analysis.