Inrush Current Limiters (ICL)

Part Number	Description / PDF	Quantity
B57211P0509M301 TDK EPCOS	ICL 5 OHM 20% 5A 13MM	1241
B57364S0409M000 TDK EPCOS	ICL 4 OHM 20% 21MM	663
B57236S0121M000 TDK EPCOS	ICL 120 OHM 20% 11.5MM	0
B59204J0130B010V60 TDK EPCOS	ICL 100 OHM 25% 19MM	3228
B57237S0259M051 TDK EPCOS	ICL 2.5 OHM 20% 6.5A 15MM	650
B59750C0120A070 TDK EPCOS	PTC THERMISTOR C 750-A 120-A 70	577
B57211P0809M301 TDK EPCOS	ICL 8 OHM 20% 4A 13MM	670
B57153S0100M051 TDK EPCOS	ICL 10 OHM 20% 2A 8.5MM	1547
B57213P0259M351 TDK EPCOS	ICL 2.5 OHM 20% 6.5A 14.5MM	0
B57237S0220M051 TDK EPCOS	ICL 22 OHM 20% 2.8A 15MM	559
B57236S229M TDK EPCOS	ICL 2.2 OHM 20% 11.5MM	3197
B57364S2209A2 TDK EPCOS	ICL 2 OHM 20% 12A 21MM	0
B57213P0109M301 TDK EPCOS	ICL 1 OHM 20% 7.5A 14.5MM	0
B57236S0160M051 TDK EPCOS	ICL 16 OHM 20% 2.9A 11.5MM	3484
B59215J0130A020 TDK EPCOS	HOUSED PTC THERMISTORS AS ICL, 2	0
B57464S0509M000 TDK EPCOS	ICL 5 OHM 20% 9.5A 26MM	409
B57213P0409M351 TDK EPCOS	ICL 4 OHM 20% 6A 14.5MM	1497
B57236S0309M000 TDK EPCOS	ICL 3 OHM 20% 11.5MM	3006
B57237S0709M000 TDK EPCOS	ICL 7 OHM 20% 4.2A 15MM	0
B57153S150M54 TDK EPCOS	ICL 15 OHM 20% 1.8A 8.5MM	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.