Inrush Current Limiters (ICL)

Image	Part Number	Description / PDF	Quantity	Rfq
	ST20001C Wickmann / Littelfuse	ICL 20 OHM 20% 300MA 8.89MM	0
	ST15004C Wickmann / Littelfuse	ICL 15 OHM 20% 4A 19.56MM	0
	ST5R004B Wickmann / Littelfuse	ICL 5 OHM 20% 4A 15.24MM	0
	ST5R008B Wickmann / Littelfuse	ICL 5 OHM 20% 8A 29.21MM	0
	ST10005B Wickmann / Littelfuse	ICL 10 OHM 20% 5A 19.05MM	0
	ST2R503B Wickmann / Littelfuse	ICL 2.5 OHM 20% 3A 15.24MM	0
	ST5R007B Wickmann / Littelfuse	ICL 5 OHM 20% 7A 23.5MM	0
	ST30002B Wickmann / Littelfuse	ICL 30 OHM 20% 2A 13.97MM	0
	ST25002C Wickmann / Littelfuse	ICL 25 OHM 20% 2A 13.97MM	0
	ST2R509B Wickmann / Littelfuse	ICL 2.5 OHM 20% 9A 22.86MM	0
	ST33001B Wickmann / Littelfuse	ICL 33 OHM 20% 1A 13.97MM	0
	ST16002D Wickmann / Littelfuse	ICL 16 OHM 20% 2A 15.24MM	0
	ST8R006B Wickmann / Littelfuse	ICL 8 OHM 20% 6A 24.76MM	0
	ST2R510B Wickmann / Littelfuse	ICL 2.5 OHM 20% 10A 30.5MM	0
	ST30003B Wickmann / Littelfuse	ICL 30 OHM 20% 3A 17.78MM	0
	ST20100B Wickmann / Littelfuse	ICL 200 OHM 20% 100MA 9.4MM	0
	ST10006B-R0 Wickmann / Littelfuse	ICL 10 OHM 20% 6A 29.85MM	0
	ST40002B Wickmann / Littelfuse	ICL 40 OHM 20% 2A 18.42MM	0
	ST33001D Wickmann / Littelfuse	ICL 33 OHM 20% 500MA 11.4MM	0
	ST5R002B Wickmann / Littelfuse	ICL 5 OHM 20% 2A 15.24MM	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.