Inrush Current Limiters

SL12 1R308

SL12 1R308 - 1.3Ω 8A Inrush Current Limiter NTC | Ametherm

The Ametherm SL12 1R308 is a 1.3 ohm ±20% inrush current limiting NTC thermistor rated for 8 A maximum steady-state current up to +65 °C, housed in a 12 mm radial-leaded disc package with 0.512 inch (13.00 mm) lead spacing. It absorbs up to 40 J of recommended inrush energy and is engineered to suppress the capacitive charge surge that occurs when power is first applied to capacitive loads such as switch-mode power supplies, motor drives, and audio amplifiers. An inrush current limiter (ICL) is a negative temperature coefficient (NTC) thermistor whose cold-state resistance is intentionally high to throttle the initial charging current, then self-heats and drops to a much lower hot resistance once steady-state current flows. The ICL sits in the taxonomy of circuit protection devices alongside PTC resettable fuses, NTC surge limiters, and traditional fixed resistors, and is widely deployed as a passive, low-cost alternative to active soft-start MOSFET circuits in offline AC-DC and DC-DC converters. Key specifications of the SL12 1R308 include 1.3 Ω cold resistance at 25 °C with ±20% tolerance, an 8.00 A maximum steady-state current rating up to +65 °C, and a maximum recommended inrush energy rating of 40 J. The device is UL approved per the Mouser listing and is supplied in a radial-leaded through-hole package suitable for hand or wave soldering on conventional PCBs. The thermistor body is constructed from a metal-oxide ceramic whose resistance decreases exponentially with temperature, governed by its beta constant. The SL12 1R308 belongs to Ametherm's SL12 series, which is sized for 12 mm diameter discs and offers a family of cold-resistance values to cover a broad range of steady-state current requirements from sub-amp to tens-of-amps designs. Typical applications include AC-DC switch-mode power supply input stages, motor soft-start circuits, audio amplifier power rails, capacitor bank pre-charge circuits, and UPS battery input protection. Designers select the SL12 1R308 when 8 A steady-state current and approximately 40 J of pulse energy absorption are required in a cost-effective, passive, single-component solution. When designing with this device, confirm that the maximum inrush energy of the load capacitor bank does not exceed the SL12 1R308's 40 J rating, and account for the voltage drop across the thermistor at hot resistance when calculating worst-case load regulation. This page synthesizes distributor pricing, UL certification status, drop-in alternatives, and practical design notes not found in the manufacturer datasheet alone.