SL12 22101 - 220Ω NTC Inrush Current Limiter, 1A | Ametherm
MPN: SL12 22101 ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.55 | $0.55 |
| 10 | $0.49 | $4.90 |
| 100 | $0.42 | $42.00 |
| 500 | $0.36 | $180.00 |
| 1,000 | $0.32 | $320.00 |
SL12 22101 Overview
An NTC inrush current limiter is a passive discrete component whose resistance drops sharply as its body self-heats from load current. At turn-on, the cold thermistor presents a high impedance that slows the charging of downstream bulk capacitors and limits the peak rectifier or MOSFET stress; once steady-state current flows, the device warms and settles at a low hot resistance (4.20 Ω at 100 % of max current per the Ametherm datasheet), so conduction losses remain small. Compared with fixed resistors, PTC fuses or active MOSFET circuits, the NTC ICL is simpler, cheaper, and self-resetting, and it is widely used as the first-line protection element on AC-DC converter inputs.
Key features of the SL12 22101 include a 220 Ω ±20 % cold resistance, 1.00 A maximum steady-state current at 65 °C, 30 J maximum recommended inrush energy, 65 J actual failure instantaneous energy, 8.14 Ω resistance at 50 % of max current, 142 °C body temperature at 100 % of max current, a 12 mW/°C dissipation constant, and a 50 s thermal time constant. The disc uses Ametherm Material Type L and carries UL approval for inrush current limiting service, simplifying safety submissions for end products.
Architecturally, the device is a pressed-disc NTC thermistor with tinned copper-clad steel leads (0.5 mm ±0.1 mm diameter) suitable for through-hole mounting. The 12 mm body diameter and 5.5 mm thickness support sufficient thermal mass to absorb the 30 J inrush pulse without exceeding the 65 J failure limit, while the 50 s thermal time constant lets the device recover between repeated turn-on cycles.
Typical applications include AC-DC switch-mode power supply input protection, audio amplifier power-rail soft-start, motor drive inrush limiting, transformer and solenoid inrush suppression, and general capacitive-load surge current limiting where a self-resetting, cost-effective solution is preferred over a fixed resistor or active circuit.
When designing with this device, derate the steady-state current for ambient temperatures above 65 °C and ensure that expected turn-on energy (½·C·V²) plus safety margin remains below the 30 J recommended rating. Allow adequate spacing around the disc for free-air cooling and consider a bypass relay or active bypass circuit if continuous conduction losses become significant at full operating temperature.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the Ametherm datasheet, including a parametric comparison against equivalent ICLs from competing suppliers and a checklist for selecting the correct cold resistance for a given bulk-capacitance load.
Drop-in alternatives for SL12 22101 — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
SL12 22101-A
✅ Drop-In📋 Reference alternative (not in catalog)
SL12 22101-B
✅ Drop-In📋 Reference alternative (not in catalog)
SL12 22101-AT
✅ Drop-In📋 Reference alternative (not in catalog)
SL1222101
✅ Drop-In📋 Reference alternative (not in catalog)
SL12 22101 Specifications
| Component Type | NTC Inrush Current Limiter (ICL) |
| Cold Resistance @ 25 °C | 220 Ω ±20 % |
| Maximum Steady-State Current @ 65 °C | 1.00 A |
| Maximum Recommended Inrush Energy | 30 J |
| Actual Failure Instantaneous Energy | 65 J |
| Resistance @ 100 % Max Current | 4.20 Ω |
| Resistance @ 50 % Max Current | 8.14 Ω |
| Body Temperature @ 100 % Max Current | 142 °C |
| Dissipation Constant | 12.0 mW/°C |
| Thermal Time Constant | 50 s |
| Material Type (Beta and Curve) | L |
| Body Diameter (D) | 12.0 mm ±0.5 mm |
| Body Thickness (T) | 5.5 mm ±0.5 mm |
| Lead Diameter | 0.5 mm ±0.1 mm |
| Lead Spacing (S) | 7.8 mm (nominal) |
| Mounting Type | Through-hole, radial leads |
| UL Approval | Yes (Inrush Current Limiter) |
SL12 22101 Pin Configuration
| Pin 1 | Lead 1 — Input / line-side connection (tinned copper-clad steel, 0.5 mm diameter) |
| Pin 2 | Lead 2 — Output / load-side connection (tinned copper-clad steel, 0.5 mm diameter) |
Typical Applications
SL12 22101 is suitable for 6 applications: AC-DC Switch-Mode Power Supply Input Protection, Audio Amplifier Power-Rail Soft-Start, Motor Drive Inrush Limiting, Transformer and Solenoid Inrush Suppression, Capacitive-Load Surge Current Limiting, Industrial Power Supply Protection Modules.
AC-DC Switch-Mode Power Supply Input Protection
The SL12 22101 is placed in series with the AC input or DC rail of a switch-mode power supply to limit the peak inrush that charges the bulk capacitor after the bridge rectifier. Its 220 Ω cold resistance attenuates the first-cycle surge, protecting the rectifier diodes and the input fuse, while its 30 J energy rating covers typical 100-400 µF bulk caps at universal-mains voltages. Once steady-state current flows, the disc self-heats and settles at 4.20 Ω, so conduction loss at 1 A stays around 4 W and overall efficiency is preserved. Designers choose the SL12 22101 over fixed resistors because the self-resetting NTC behavior eliminates the need for a thermal fuse and the same part handles wide-range AC input voltages without re-design.
Recommended
Audio Amplifier Power-Rail Soft-Start
In Class-D and high-power Class-AB amplifiers, the SL12 22101 is inserted between the mains rectifier and the main reservoir capacitors to limit the turn-on surge that can trip breakers or stress rectifier diodes. The 1.00 A continuous rating covers amplifier standby and idle currents, while the 30 J inrush rating easily absorbs the energy stored in typical 10 000-47 000 µF reservoir banks charged to ±50 V rails. Because the NTC ICL is self-resetting, no relay bypass is required for short soft-start transients, simplifying the protection circuit and reducing BOM count. Compared with an NTC + relay bypass scheme, the SL12 22101 alone offers a cost-effective soft-start for amplifiers up to a few hundred watts.
Recommended
Motor Drive Inrush Limiting
Small DC motors and brushless-DC drives draw a heavy inrush when the rotor is stalled or when the bus capacitor charges at first power-on. The SL12 22101, with its 220 Ω cold resistance, slows the charging of the motor's bus capacitance and limits the stall-current spike that would otherwise overstress the input fuse or upstream MOSFET. The 1.00 A continuous rating handles typical low-power motor idle and running currents, and the 12 mm disc body tolerates the thermal cycling from repeated start-stop events thanks to its 50 s thermal time constant. Engineers favor the SL12 22101 here because its small footprint and through-hole leads simplify placement near the input connector, and its UL approval eases safety certification of the drive module.
Recommended
Transformer and Solenoid Inrush Suppression
When 50/60 Hz transformers or DC solenoids energize, the saturating inductance and the collapsing magnetic field can draw many times the rated current for the first few cycles. The SL12 22101 is wired in series with the primary winding to suppress that surge; its 220 Ω cold impedance limits the first-cycle peak while its 30 J inrush rating covers typical 50-200 VA control transformers and mid-size solenoids. After a few cycles the disc has warmed enough that voltage drop and power dissipation stay low, preserving regulation. Compared with PTC thermistors, the NTC ICL resets faster and provides tighter inrush limits on repeated energizations.
Recommended
Capacitive-Load Surge Current Limiting
Long cable runs, large filter capacitors, and high-C bus structures can pull destructive surge currents when DC is first applied. The SL12 22101 acts as a current-limiting element in series with the load, with its 220 Ω cold resistance acting as the soft-charge resistor and its 30 J rating covering the energy stored in typical 1000-4700 µF capacitor banks at 24-48 V. Once charged, the disc drops to 4.20 Ω so that regulation is minimally impacted. This application often appears in industrial control modules, telecom rectifier inputs, and battery-backed DC distribution boards, where the SL12 22101 is preferred over fixed resistors because it is self-resetting and requires no firmware-controlled pre-charge circuit.
Recommended
Industrial Power Supply Protection Modules
Industrial 24 V and 48 V power systems feeding PLCs, sensors, and motor starters require robust inrush protection that meets UL and IEC standards. The SL12 22101, with its UL approval for inrush current limiting service, is integrated into DIN-rail power supplies and front-end protection modules. The 12 mm disc body fits a compact through-hole footprint, and the 1.00 A continuous rating covers the 24 V auxiliary rail commonly used to power interface electronics. Designers value the Ametherm Material Type L curve for predictable derating, and use the SL12 22101 alongside a TVS diode or PTC for a complete two-stage protection circuit.
Recommended
Recommended Products Summary
Engineering reference data for SL12 22101 — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | SL12 22101-A | SL12 22101-B | SL12 22101-AT | SL1222101 |
|---|---|---|---|---|---|
| Brand | Vishay Ametherm | Vishay Ametherm | Vishay Ametherm | Vishay Ametherm | Vishay Ametherm |
| Package | 12 mm radial disc (D=12.0 mm, T=5.5 mm, lead spacing 7.8 mm) | 12 mm radial disc - same | 12 mm radial disc - same | 12 mm radial disc - same | 12 mm radial disc - same |
| Cold Resistance @ 25 °C | 220 Ω ±20 % | 220 Ω ±20 % | 220 Ω ±20 % | 220 Ω ±20 % | 220 Ω ±20 % |
| Maximum Steady-State Current | 1.00 A @ 65 °C | 1.00 A | 1.00 A | 1.00 A | 1.00 A |
| Maximum Recommended Inrush Energy | 30 J | 30 J | 30 J | 30 J | 30 J |
| Actual Failure Instantaneous Energy | 65 J | 65 J | 65 J | 65 J | 65 J |
| Resistance @ 100 % Max Current | 4.20 Ω | 4.20 Ω | 4.20 Ω | 4.20 Ω | 4.20 Ω |
| UL Approval | Yes | Yes | Yes | Yes | Yes |
Key Differentiators
- Self-resetting NTC ICL with low hot resistance (vs Fixed power resistor)
- 12 mm disc body with UL approval (vs Larger SL15/SL22 series)
- Multiple drop-in same-brand suffixes available (vs Single-SKU competitor parts)
Design Notes
Estimated: at 1.00 A steady-state current, the SL12 22101 dissipates approximately 4.2 W (P = I² × R_hot = 1² × 4.20 Ω). With a dissipation constant of 12 mW/°C, the temperature rise above ambient is roughly 350 °C in free air, but the disc stabilizes at 142 °C body temperature per the Ametherm datasheet, indicating that in practice the part is cooled by its leads and surrounding PCB copper. Allow at least 5 mm clearance between adjacent components and consider thermal vias under the lead land pattern for improved heat extraction.
Do not select the SL12 22101 based on cold resistance alone - the maximum recommended inrush energy of 30 J is the harder limit. Compute the worst-case inrush energy as ½·C·V² for capacitive loads and add a 25 % safety margin; if ½·C·V² × 1.25 exceeds 30 J, step up to the next-size SL15- or SL22-series Ametherm part. Also, never assume the 65 J failure energy is a working limit - it is the destruction threshold and the part will degrade if it is repeatedly pulsed near it.
Place the SL12 22101 as close as possible to the input connector or bridge rectifier so that the high-impedance cold path is in series with the full bulk capacitance. Use 0.5 mm or larger lead-diameter pads with at least 1 oz copper to spread heat; the 0.5 mm leads (per Ametherm datasheet) are not designed to carry more than 1 A continuously. Provide strain relief if the device sits near a moving cable or connector to prevent lead fatigue over thermal cycling.
Compliance Information
RoHS and REACH compliance inferred from Ametherm product page; UL approval for inrush current limiting service confirmed by Mouser listing. AEC-Q100 not applicable for a passive inrush limiter. Halogen-free status not stated in the verified data.
