BLM31KN121SN1L

BLM31KN121SN1L is a ferrite bead from Murata in a 1206 (3216 metric) case with an impedance of 120 Ω ±25% at 100 MHz — the low-impedance, high-current end of the BLM31 line, and Murata's PIM record lists this part as In Production. The current figures carry their temperature points: rated 6 A at +85 °C and 4 A at +125 °C, with DC resistance of just 0.009 Ω maximum, across −55 °C to +125 °C; dimensions 3.2 x 1.6 x 1.6 mm. The final L is the 180 mm embossed-tape reel at 2,500 pieces. The selection point is power-rail noise suppression where the rail current is real: at 6 A class, DCR is the specification, because every milliohm is heat and voltage drop. Selection advice: quote the rating with its temperature — a design that runs the bead at +125 °C ambient has a 4 A part, not a 6 A part.