Inrush Current Limiters (ICL)

Part Number	Description / PDF	Quantity
B57236S0800M051 TDK EPCOS	ICL 80 OHM 20% 1.6A 11.5MM	2977
SL08 4R003 Ametherm	ICL 4 OHM 20% 3A 8MM	4669
MS32 50006-B Ametherm	ICL 50 OHM 25% 6A 31MM	9
SL32 5R020 Ametherm	ICL 5 OHM 20% 20A 31MM	0
B59412C1130B070 TDK EPCOS	ICL 120 OHM 25% 15MM	218
MF72-001.3D15 Cantherm	ICL 1.3 OHM 20% 8A 17.5MM	0
SL22 40005-B Ametherm	ICL 40 OHM 20% 5A 22MM	0
CL-50A Thermometrics (Amphenol Advanced Sensors)	ICL 7 OHM 25% 5A 19.56MM	0
SL18 5R006-A Ametherm	ICL 5 OHM 20% 6A 19MM	0
MF72-003D13 Cantherm	ICL 3 OHM 20% 6A 15.5MM	0
B57235S0609M051 TDK EPCOS	ICL 10 OHM 20% 4A 9.5MM	3976
CL-101A Thermometrics (Amphenol Advanced Sensors)	ICL 500 MOHM 25% 16A 23.62MM	0
SL22 0R712-B Ametherm	ICL 700 MOHM 25% 12A 22MM	0
SG312 Ametherm	ICL 7 OHM 15% 4A 15.24MM	0
CL-70B Thermometrics (Amphenol Advanced Sensors)	ICL 16 OHM 4A 19.56MM	0
MS35 2R035 Ametherm	ICL 2 OHM 35A 35MM	105
SL08 33001 Ametherm	ICL 33 OHM 20% 1.3A 8MM	146
MF72-003D9 Cantherm	ICL 3 OHM 20% 4A 11MM	5020
SL15 80002 Ametherm	ICL 80 OHM 25% 2A 16MM	187
SL22 20007-A Ametherm	ICL 20 OHM 25% 7A 22MM	0

Inrush Current Limiters (ICL)

1. Overview

Inrush Current Limiters (ICL) are electronic components designed to suppress peak currents during device startup, protecting circuits from thermal and electrical stress. These transient currents, often 10-100 times higher than steady-state levels, occur in capacitive or inductive loads like power supplies, motors, and transformers. Modern electronics increasingly rely on ICLs to ensure system reliability, comply with safety standards, and extend product lifespans.

2. Main Types & Functional Classification

Type	Functional Characteristics	Application Examples
NTC Thermistor ICL	Resistance decreases with temperature rise, self-resetting capability	Switching power supplies, LED drivers
PTC Thermistor ICL	Resistance increases with temperature, latching protection	Motor start circuits, battery management systems
Active ICL	Electronic control using MOSFETs/IGBTs with precise timing	High-precision industrial equipment
Hybrid ICL	Combines passive and active elements for optimized performance	Electric vehicle charging stations

3. Structure & Composition

ICLs typically consist of three key elements:

Sensing Element: Thermally responsive material (e.g., NTC ceramic) or semiconductor junctions
Conductive Path: Silver/palladium electrodes in thermistors or MOSFET channels in active devices
Encapsulation: Epoxy or ceramic coatings for environmental protection

Active ICLs additionally integrate control ICs, gate drivers, and heat dissipation structures.

4. Key Technical Specifications

Parameter	Description	Importance
Maximum Steady-State Current (I_max)	Rated operational current after inrush suppression	Determines continuous load capacity
Response Time (t_response)	Time to activate current limiting function	Protects against fast transient events
Clamping Voltage (V_clamp)	Maximum voltage during limiting operation	Prevents downstream component damage
Operating Temperature Range	Functional temperature limits	Ensures reliability in extreme environments
Energy Absorption (I t)	Total energy handling capability	Defines survival under fault conditions

5. Application Fields

Major industries utilizing ICLs include:

Consumer Electronics: Power adapters, HVAC systems
Industrial: Variable frequency drives, welding machines
Automotive: EV charging stations, onboard chargers
Medical: MRI power systems, patient monitors

Typical case: NTC ICLs reduce 50A startup surges to 5A in 500W switching power supplies.

6. Leading Manufacturers & Products

Manufacturer	Product Series	Key Features
TDK Corporation	B59xxx Series	High-reliability NTCs for automotive applications
Littelfuse	PTCLxxx Series	AEC-Q100 qualified PTC devices
Bel Fuse	0Zxxx Series	Multi-layer ceramic thermistors
EPCOS (TDK)	B25xxx Series	Hybrid ICLs with integrated sensors

7. Selection Guidelines

Critical factors for proper ICL selection:

Match I_max with system steady-state requirements (+20% margin)
Verify V_rated exceeds peak AC voltage by 50%
Consider ambient temperature effects on performance
Evaluate reset time for thermistor-based solutions
For active ICLs: Confirm compatibility with control signals

Example: A 240VAC motor drive requires an ICL with 15A I_max and 300V_clamp.

8. Industry Trends

Emerging developments include:

Miniaturization: 0603-sized active ICLs for mobile devices
Wide bandgap integration: SiC/GaN-based hybrid devices
Smart ICLs: Embedded current monitoring and diagnostics
Material innovation: Graphene-enhanced thermistors

Market growth driven by EV charging infrastructure and renewable energy systems, projected at 7.2% CAGR through 2027.