Inductance Converter

Inductance is the ability to store energy in a magnetic field when current flows, measured in henries (H). Most practical inductors are microhenries (µH) to millihenries (mH) — the henry itself is a huge unit, used for large audio crossovers and line-frequency chokes. RF inductors are nH to µH; switching power supply chokes span 10-500 µH; the primary of a small transformer might be in the millihenry range. Inductance is the electromagnetic opposite of capacitance: caps store energy in electric fields, inductors in magnetic fields, and the two together form every resonant circuit from crystal oscillators to wireless charging pads.

The henry (H) is the SI unit, defined via the volt and the ampere: a 1 H inductor develops 1 V across it when current changes at 1 A/s. The fundamental relationship V = L × di/dt makes inductors behave opposite to capacitors. Inductance depends on coil geometry and core material: air-core inductors for RF (low losses, limited inductance, no saturation); ferrite cores for µH-mH at RF and switching frequencies (permeability 100-5000); iron laminations for 50/60 Hz transformers (high permeability but thick lams keep eddy-current losses down); soft magnetic amorphous/nanocrystalline for high-efficiency switchers; powdered-iron cores for RF power where ferrite would saturate.

Inductors have a Q factor — the ratio of inductive reactance to resistance at the working frequency. Q = ωL/R. High-Q inductors (100+) make good resonators; low-Q inductors (1-10) are lossy but fine for filtering. Saturation current is the current at which the core's magnetic permeability drops sharply, effectively disappearing the inductance. Exceed Isat in a switching regulator and you get an instant current spike and either a blown MOSFET or a magic-smoke event.

mH to H: divide by 1,000. µH to mH: divide by 1,000. nH to µH: divide by 1,000. Inductors in series add: L_total = L1 + L2 + L3 (like resistors). In parallel, inverse-sum: 1/L = 1/L1 + 1/L2 (also like resistors). Energy stored: E = ½ L I². A 100 µH inductor at 3 A holds 450 µJ. Impedance at frequency f: Z = 2πfL. A 10 µH inductor at 1 MHz looks like 62.8 Ω; at 100 MHz, 6.28 kΩ.

• Henry (H)
• Millihenry (mH)
• Microhenry (µH)
• Nanohenry (nH)
• Picohenry (pH)
• Kilohenry (kH)
• Abhenry
• Stathenry (esu)

• Units scale. 1 H = 1,000 mH = 1,000,000 µH = 10⁹ nH. Misreading SMD inductor markings by a factor of 1,000 is common. Chip inductors often use a 3-digit code: '100' is 10 × 10⁰ = 10 µH; '221' is 22 × 10¹ = 220 µH; '4R7' means 4.7 µH.
• Core saturation. A core that saturates loses inductance instantly and lets current spike. DC-DC converters can fail this way within microseconds. Always check saturation current (Isat) in the datasheet — not just the DC resistance (DCR) rating.
• Self-resonant frequency (SRF). Every inductor has parasitic capacitance between turns, forming an LC tank. Above SRF the component behaves capacitively. A 10 µH chip inductor with 50 MHz SRF is useless at 100 MHz — use a smaller value or different topology.
• Core losses vs copper losses. At low currents, wire resistance (I²R) dominates. At high frequencies or near saturation, hysteresis and eddy losses in the core dominate. Switching-supply inductor datasheets give loss curves at multiple frequencies.
• DC bias reduces effective inductance. In powdered-iron and some ferrite cores, high DC current reduces permeability — a 10 µH inductor at 0 A might be 8 µH at rated current. Datasheets show L-vs-I curves.
• Coupled inductor pitfalls. Two inductors near each other share flux. A transformer is the intentional case; an unintentional coupling in a buck-boost converter can cause cross-regulation problems.

• RF inductor (WiFi, Bluetooth matching network): 1-100 nH.
• Choke in small-signal amp: 10-100 µH.
• Buck converter output inductor (1 MHz, 1 A): 10-47 µH.
• Audio crossover inductor (woofer): 0.1-5 mH, air-core 1 mm wire.
• Line-frequency choke for EMI filtering (60 Hz): 1-100 mH.
• Linear power supply transformer primary (120 V, 60 Hz): ~10 H equivalent inductance.
• Motor windings (small BLDC): 0.5-5 mH per phase.
• Induction cooktop work coil: 100-200 µH.
• Wireless charger TX coil (Qi standard): ~24 µH.
• Large power-factor correction inductor: 5-20 mH at 20+ A.

• For switchers, check saturation current rating, not just inductance. Peak current (including ripple) must stay below Isat.
• For RF, use air-core or ferrite, not iron (high losses at high frequency).
• For filters, choose based on self-resonant frequency — the component becomes capacitive above SRF.
• Shielded inductors contain their flux — essential near sensitive analog circuits.
• Coupled inductors can halve the total inductor count in multi-output converters but demand careful layout.

Related: Capacitance Converter · Electrical Resistance Converter · Magnetic Flux Converter.