120 µH wirewound in 1812 — DC bias and AC loss trade-offs
The LQH43NN121J03L is a drum-core wirewound inductor from Murata's LQH43 series, delivering 120 µH ±5% in the standard 1812 (4532 Metric) SMD footprint. The 150 mA current rating is the DC bias limit before inductance begins to roll off — stay below this for the full 120 µH value. 3 Ω max DCR sets the I²R self-heating floor: at 150 mA the copper loss is 67.5 mW, which raises the internal temperature above the 105 °C max ambient. The unshielded construction means the external field couples into adjacent traces — keep sensitive analog or RF routing at least one part-width away.
Q factor and self-resonant frequency — the usable band
Q is 40 at 796 kHz, placing the peak efficiency in the low hundreds of kHz — typical for buck converters switching at 200–500 kHz. Above 6.2 MHz the inductor becomes capacitive; the self-resonant frequency sets the hard ceiling for the application. The 1 MHz test frequency for inductance means the 120 µH value is characterised near the top of the useful range. Ferrite core material gives stable inductance from -40 °C to 105 °C, with permeability dropping off above the Curie point.