PTC Resettable Fuse Symbols, Tutorials, Manufacturers, and Application Notes

Ptc Resettable Fuse

PTC resettable fuses (PPTC, Polymeric Positive Temperature Coefficient), also known as self-resetting fuses, are overcurrent protection devices based on the principle of positive temperature coefficient thermistors. They automatically trip (limit current) during an overcurrent event and reset upon cooling after the fault is cleared, eliminating the need for replacement. They are widely used in electronics, telecommunications, automotive, and battery applications.

PTC Resettable Fuses
I. Core Principle (Polymeric PPTC)
Normal State (Low-Resistance Conductive): Composed of a polymer matrix (e.g., polyethylene) combined with conductive particles (carbon black). At low temperatures, the polymer is in a crystalline state, and the conductive particles are closely connected, forming a low-resistance path (tens of milliohms to several ohms).
Overcurrent Operation (High-Resistance Protection): Excessive current → Joule heating → Polymer melts and expands (amorphous state) → Conductive network breaks → Resistance surges (up to megohms) → Current is limited to microamperes/milliamps → Protects downstream components.
Self-Recovery (Cooling Reset): Fault resolved → Component cools → Polymer recrystallizes → Conductive path restores → Circuit returns to normal operation.

II. Key Parameters (Essential for Selection)
Ihold (Holding Current): The maximum current at which the device remains conductive without tripping during long-term operation at 25°C. Selection: Ihold > maximum operating current of the circuit (allow a margin of 1.25–2 times).
Itrip (Trip Current): The minimum current required to trigger protection; typically, Itrip ≈ 2×Ihold.
Vmax (Maximum Withstand Voltage): The highest operating voltage the component can withstand (e.g., 6V/16V/30V/60V/250V). Vmax must be greater than or equal to the system voltage.
Imax (Maximum Breaking Current): The maximum fault current that can be safely interrupted; exceeding this value will cause permanent damage.
Rmin / Rmax: Initial resistance range at room temperature (the lower, the better).
Response Time: The delay from overcurrent to high resistance (milliseconds to seconds; the higher the current, the faster the response).

III. Comparison with Traditional Disposable Fuses
Table
Characteristic    PTC Resettable Fuse    Disposable Fuse
Protection Mechanism    Resistance surge (current limiting)    Metal melting (circuit breaking)
Post-trigger State    High resistance (recoverable)    Permanent open circuit
Replacement Required    Not required (auto-reset)    Must be replaced manually
Response Speed    Slow (ms–s)    Extremely fast (ns–μs)
Applications    Frequent overloads, short circuits, difficult maintenance    Severe short circuits, one-time protection

IV. Packaging and Types
Surface Mount (SMD): 0402/0603/0805/1206/1812/2920 → PCB surface mounting, consumer electronics.
Surface-mount PTC Resettable Fuses
Through-hole Radial: Axial / Radial Leads → Power supplies, industrial control, automotive electronics.
Through-hole PTC Resettable Fuses
Battery-specific: Thin profile, low internal resistance → Lithium battery packs, mobile phone / tablet protection.
Battery-specific PTC Resettable Fuses
CPTC (Ceramic PTC): High-temperature resistance, excellent stability, used in high-temperature / high-voltage applications.

V. Typical Applications
Consumer Electronics: Overcurrent/short-circuit protection for USB ports, chargers, power banks, hard drives, and monitors.
Battery Packs: Overcharge, over-discharge, overcurrent, and thermal runaway protection for lithium-ion and power batteries.
Automotive Electronics: Headlights, motors, ECUs, in-vehicle chargers, battery management systems.
Communications / Industrial: Switches, routers, PLCs, sensors, motor stall protection.

VI. Selection and Usage Guidelines
Current: Derate according to the maximum ambient temperature (Ihold decreases at high temperatures).
Voltage: Vmax ≥ peak operating voltage (e.g., select ≥16V for a 12V system).
Fault Current: Ensure Imax > expected maximum short-circuit current.
Operating Time: Select fast-acting types for sensitive circuits.
Layout: Place away from heat-generating components, ensure adequate heat dissipation, and avoid false tripping.

VII. Advantages and Disadvantages
Advantages: Reusable, maintenance-free, compact size, long service life, suitable for automated installation.
Disadvantages: Residual voltage/leakage current, slower response than fuses, performance degradation at high temperatures, slightly higher cost.

Ptc Resettable Fuse Symbol

There is no globally standardized symbol for PTC resettable fuses (self-resetting fuses), but the following common representations are typically used in circuit diagrams:

1. Common domestic/industry symbols (most widespread)
Symbol: A rectangular box containing a straight line (distinguished from the wavy line used for traditional fuses).
Text label: F (Fuse), FU, or PTC (e.g., F1, PTC1).

PTC Resettable Fuse Symbol
2. International / Standard-Preferred Symbols
Graphic: A rectangular box containing two diagonal arrows (↔), symbolizing “recoverable, resettable.”
Text Label: RT (Resistance Thermistor) or PPTC.

3. Simplified / Generic Symbols
Use the standard fuse symbol (rectangle + wavy line) directly, but include the text “PTC/Resettable” in the BOM or next to the component.

Standard fuse symbol
4. Comparison with traditional fuse symbols
Table
Component Type    Graphic Symbol    Key Difference
Disposable fuse    Rectangle + wavy line (~~~)    Cannot be restored after blowing
PTC resettable fuse    Rectangle + straight line / double arrows    Automatically resets after overcurrent

Ptc Resettable Fuse Tutorial

I. What Is a PTC?
A PTC (Positive Temperature Coefficient Thermistor) is a resettable fuse—a protective component that automatically increases its resistance upon overcurrent and automatically returns to normal after cooling.
Normal: Low resistance (conductive)
Overcurrent / Short circuit: Instantly becomes high resistance, providing current-limiting protection
Fault resolved: Automatically returns to normal after cooling; no need to replace the component

II. Key Parameters
1. Ihold​ Holding Current
The maximum current at which the device will never trip during long-term operation at 25°C. → Selection principle: Ihold ≥ Circuit maximum operating current × 1.2–1.5

2. Itrip​ Trip Current
The current at which protection begins; generally ≈ 2×Ihold

3. Vmax​ Maximum Withstand Voltage
The highest voltage the PTC can withstand. → Must be ≥ system voltage (e.g., for a 12V system, select ≥16V)

4. Rmin​ / Rmax​
Resistance at room temperature; the lower the value, the lower the power loss.

5. Imax​ Maximum Short-Circuit Current
Exceeding this value will permanently damage the PTC; it must be greater than the maximum possible short-circuit current in the circuit.

III. Working Principle (Super Simplified Version)
Normal temperature: Conductive particles within the polymer are connected → Low resistance
Overcurrent heating: Polymer expands → Conductive network breaks → Resistance skyrockets
Current is limited to a very low level → Protects downstream components
Power off / Fault resolved → Cooling → Conductivity restored

IV. PTC vs. Disposable Fuses
Table Item PTC Resettable Disposable Fuse High resistance after tripping, recoverable Fuse blows, open circuit Recovery Automatic Must be replaced Response Milliseconds to seconds Faster (microseconds) Applications Frequent overloads, difficult maintenance Strong short-circuit protection
Conclusion: If maintenance-free, repeated protection is required → Use PTC.

V. Most Practical: Selection Steps (Engineering Standards)
Determine operating voltage: Select Vmax ≥ operating voltage
Determine maximum operating current: Select Ihold ≥ operating current × 1.2
Determine ambient temperature: Derate for high temperatures (Ihold decreases by approximately 30% at 50°C)
Select package: Surface-mount 0603/0805/1206 or through-hole
Confirm short-circuit current does not exceed Imax

VI. Typical Applications (Most Common)
USB ports, Type-C overcurrent protection
Microcontrollers, sensors, module power supplies
Motor stall protection
Battery pack (lithium) protection boards
Car electronics, audio systems, LED drivers

VII. Circuit Symbols (Ready for Schematic Use)
Most common: Rectangle + straight line, labeled PTC1 / F1
International standard: Rectangle + double-headed arrow ↔
Simplified: Standard fuse symbol + labeled PTC

Ptc Resettable Fuse Application Notes

PTC Resettable Fuse Application Note (Full Version)

I. Product Overview
PTC (Positive Temperature Coefficient) resettable fuses, also known as PPTC self-resetting fuses, are dual-protection components that provide both overcurrent and overheat protection.
During normal operation, they are in a low-resistance, conductive state; when the circuit experiences overcurrent, short circuits, or overheating, the resistance rises sharply and instantly, limiting the current to a minimal value to provide protection; after the fault is cleared and the temperature drops, they automatically return to a low-resistance state, requiring no replacement and allowing for repeated use.

II. Operating Principle
Normal Operation: The component temperature is low, the internal conductive path is intact, and resistance is minimal, causing no impact on circuit operation.
Overcurrent Trip: Excessive current → Joule heating → Expansion of internal structure → Disruption of conductive path → Drastic increase in resistance → Current is limited.
Automatic Recovery: Fault resolved → Temperature drops → Structure returns to normal → Conductive path re-establishes.

III. Meaning of Key Electrical Parameters
Ihold Holding Current
The maximum current at which the device remains inactive during long-term operation at 25°C.
Itrip Trip Current
The minimum current required to trigger protection, typically 1.8–2.5 × Ihold.
Vmax Maximum Withstand Voltage
The highest operating voltage the device can withstand; it must exceed the system operating voltage.
Imax Maximum Fault Current
The maximum short-circuit current the device can safely withstand; exceeding this value will cause permanent damage.
R0 Initial Resistance
The on-resistance at room temperature; the lower the value, the lower the power dissipation.

IV. Typical Applications
USB, Type-C ports, and charging port overcurrent protection
Power modules, adapters, and charger output protection
Microcontroller, sensor, and communication module protection
Motor stall, fan, and water pump overcurrent protection
Lithium-ion battery packs, power banks, and power tool protection
Automotive electronics, LED lighting, and security equipment
Industrial control boards, interface circuits, and protection for short-circuit-prone ports

V. Usage Instructions (Wiring)
Connect in series within the power supply circuit; typically connect to the positive terminal (VCC).
Connect one end to the power supply input and the other to the load.
Overcurrent protection is achieved without the need for parallel components.

VI. Basic Selection Principles
Vmax ≥ Operating Voltage (recommended to leave a margin of 20% or more)
Ihold ≥ Maximum operating current of the circuit × 1.2–1.5
Derate for use in high-temperature environments (the higher the temperature, the lower the Ihold)
Avoid proximity to high-power heat-generating components to prevent false tripping
Do not connect multiple PTCs in parallel (uneven current distribution may cause burnout)

VII. Features and Advantages
Automatically resets; maintenance-free and replacement-free
Compact size, suitable for high-density surface-mount or through-hole installation
Rapid response, with actuation times ranging from milliseconds to seconds
Long service life, capable of withstanding over 100,000 actuation cycles
No open flames or explosion risk, ensuring high safety

VIII. Precautions (Important)
PTCs provide only overcurrent and overheat protection; they do not offer lightning or ESD protection
For ESD and surge protection, use in conjunction with TVS or MOV varistors.
A slight leakage current remains after actuation; not suitable for ultra-low-power circuits.
Conductive resistance causes slight voltage drop and heat generation; exercise caution in high-current circuits.
Power must be disconnected and the device allowed to cool for a period of time after tripping to fully recover.
Must not be used as a direct replacement for disposable fuses in high-safety-critical applications (e.g., main power supply lines).

IX. Differences from Standard Fuses
Disposable fuses: Open circuit upon melting; must be replaced.
PTC resettable fuses: Current-limiting protection; automatically resets.

Ptc Resettable Fuse Manufacturers

The leading manufacturers of PTC resettable fuses (PPTC) are divided into top international brands and high-quality domestic manufacturers, covering all application scenarios including consumer electronics, automotive, and industrial sectors. This document provides a tiered list of key manufacturers and selection guidelines.

I. Top International Brands (Global market leaders with comprehensive technology and certifications)
1. Littelfuse (U.S., Global No. 1)
Status: The world’s largest PPTC manufacturer, with approximately 23% market share
Product Lines: Surface-mount (0402–2920), through-hole, battery-specific, high-voltage/high-current series
Advantages: Full range of certifications (UL/CSA/VDE), automotive-grade AEC-Q200, low resistance and high precision
Representative Series: nanoSMD, PTCASIA, LVR, LTP

2. Bourns (USA)
Position: Top 3 globally, strong presence in industrial and automotive sectors
Product Line: MF-R, MF-RX, MF-RH (high voltage), MF-RL (low resistance)
Advantages: High voltage rating, high reliability, suitable for industrial and automotive applications

3. TDK (Japan, including EPCOS)
Ranking: No. 2 globally, with approximately 16% market share
Product Lines: SMD0603–1812, through-hole, automotive-grade, low-power series
Advantages: Japanese quality, automotive-grade certification, low leakage current

4. Eaton Bussmann (Eaton Bussmann, USA)
Product Line: PTC, PolySwitch series, high-current / high-voltage / industrial-grade
Advantages: Strong short-circuit tolerance, suitable for power supplies / motors / industrial control

5. Schurter (Schurter, Switzerland)
Advantages: Medical / industrial control / automotive-grade, high safety certifications, long service life

6. Vishay (Vishay)
Product Lines: SMD, Through-hole, Low-resistance / High-current series
Advantages: High cost-performance ratio, suitable for consumer electronics and general applications

7. TE Connectivity
Advantages: Automotive electronics, industrial connector solutions, high reliability

II. High-Quality Manufacturers in Taiwan (Balance of Cost-Performance and Quality)
1. PTTC (Poly-Tec Technology)
Status: Taiwan’s market leader, among the top 10 globally
Product Lines: Full range of SMD, through-hole, battery protection, automotive-grade
Advantages: Fast lead times, high cost-performance ratio, ample domestic stock

2. Polytronics
Product Lines: FSMD surface-mount, through-hole, battery-specific PPTC
Advantages: Low resistance, high sensitivity, suitable for consumer electronics / fast charging

III. Mainland China Mainstream Manufacturers (High Cost-Performance Ratio, Local Supply Chain)
1. TLC Electronics
Status: China’s first SMD PPTC manufacturer, a specialized and innovative enterprise
Product Line: SMD, through-hole, high-voltage, automotive-grade
Advantages: Local R&D, fast lead times, cost-effective

2. Shanghai Kete (KET)
Status: One of China’s earliest PTC manufacturers, offering a full product range
Product Line: SMD, through-hole, high-power, demagnetization / startup types
Advantages: Low resistance and high power, comprehensive specifications, suitable for home appliances / industrial control

3. Nanjing Nanshan (NSCN)
Product Lines: JK Series (Communications-specific), MZ Series (Through-hole), SMD Series
Advantages: Certified to telecommunications industry standards; suitable for switches and patch panels

4. Other Domestic Brands
Huade, Weian, Fenghua High-Tech, Sunloong Electronics: General-purpose, high cost-performance ratio; suitable for consumer electronics

IV. Quick Guide to Manufacturer Selection (by Application)
Application    Recommended Brands    Key Advantages
Consumer Electronics / Fast Charging / USB    Littelfuse, PTTC, Jingwo, Fuzhi    Compact size, low resistance, cost-effective
Automotive Electronics / Automotive Grade    Littelfuse, Bourns, TDK, TE    AEC-Q200, high reliability
Industrial / Power Supplies / Motors    Bourns, Eaton, Schurter, Kote    High voltage, high current, long lifespan
Medical / Safety Equipment    Schurter, Littelfuse    High safety certifications, low leakage current
Cost-Priority / Volume Production    Jingwo, Kote, Nanshan, PTTC    Local supply chain, fast lead times

Ptc Resettable Fuse Schematic Symbol

There is no globally standardized IEC/GB official symbol for PTC (PPTC) resettable fuses in schematics, but there are four most commonly used standard notations in the engineering field that can be directly applied in schematics, specifications, and drawings.

1. Most Common: Standard PPTC Symbol (Rectangle + Double Arrows / Slash)
Internationally recognized and most commonly used in EDA software
plaintext
┌───────────┐
│    ←→     │
──┤           ├──
│           │
└───────────┘
Rectangular box + internal bidirectional parallel arrows (representing “resettable, recoverable”)
Text labels: PPTC, PTC, RT (thermistor)
Applications: Consumer electronics, power supplies, USB, industrial control schematics

II. Simplified Symbol (Resistor + PTC)
plaintext
     ┌───────┐
─────┤  PTC  ├─────
     └───────┘
Rectangular resistor box + internal label PTC / PPTC
Simplest and most commonly used in PCB silkscreen and quick schematics

III. Standard PTC Thermistor Symbol (IEC Style)
plaintext
     ┌───────┐
─────┤  RT   ├─────
     └───┬───┘
         │
        t+
Resistor symbol + t+ (temperature increases, resistance increases)
Designation: RT1, RT2 (Resistance Thermistor)
Suitable for: Schematics emphasizing positive temperature coefficient characteristics

IV. Comparison with Standard Fuses (Disposable vs. Resettable)
Disposable fuse FU:
plaintext
┌───────────┐
│    ———    │
──┤     ×     ├──  (broken line/wavy line in the middle)
│           │
└───────────┘
PTC Resettable Fuse PPTC:
plaintext
┌───────────┐
│    ←→     │
──┤           ├──  (No break, with reset arrow)
│           │
└───────────┘

V. Standard Notation (Part Number + Parameters)
Part Number: RT (Recommended), PPTC, PTC, F (Not Recommended, Prone to Confusion)
Example:
RT1 PPTC 0.5A/24V
PPTC1 Ihold=0.5A Vmax=24V
VI. EDA Software Libraries (Direct Call)
Altium / KiCad / Eagle:
Library Name: PPTC, PTC Fuse, Resettable Fuse
Symbol: Rectangle + Double Arrows / Rectangle + PTC

Smd Ptc Resettable Fuse

SMD PTC Resettable Fuse (Surface-Mount Self-Resetting Fuse)
1. Definition
SMD PTC = Surface Mount Device PPTC
Surface-mount polymer positive temperature coefficient (PTC) resettable fuse; suitable for automated production; provides overcurrent protection with automatic reset, eliminating the need for replacement.

2. Features
SMD package, suitable for SMT placement machine production
Compact size, thin profile
Automatically resets after tripping, no manual replacement required
Multiple protection against overcurrent, short circuit, and overheating
Long service life, capable of hundreds of thousands of cycles
Low internal resistance, low power consumption

3. Common Package Sizes (Most Standard)
0402: Ultra-compact size, low current
0603: Most common, consumer electronics
0805: General-purpose mainstream
1206: Medium current
1812: High current
2920: Very high current
Larger packages support higher currents and offer better heat dissipation.

4. Key Parameters (SMD Specific)
Ihold Holding Current: Current at which the device remains in normal operation without tripping
Itrip Trip Current: Current at which protection begins (≈2×Ihold)
Vmax Maximum Voltage Rating: 6V, 16V, 24V, 30V, 60V
R0 Initial Resistance: mΩ to Ω range; lower is better
Package: 0402/0603/0805/1206/1812/2920

5. Typical Applications (Mostly SMD PTCs)
USB and Type-C port overcurrent protection
Mobile phones, power banks, headphone charging ports
Microcontrollers, sensors, module power supplies
Cameras, LED light strips
Laptop and tablet port protection
Automotive electronics (AEC-Q200 automotive-grade SMD PTC)

6. Circuit Symbol (Standard SMD Schematic Notation)
plaintext
┌───────────┐
│    ←→     │
──┤           ├──    SMD PPTC
└───────────┘
Labels: PPTC1, RT1, PTC1

7. Wiring Method (Simplest)
Connected in series with the positive power supply terminal (VCC)
plaintext
Power Supply + → SMD PTC → Load → GND

8. Advantages vs. Through-Hole PTC
SMD: Compact size, SMT, aesthetically pleasing, stable
Through-Hole: High current capacity, shock-resistant, cost-effective

9. Leading Brands (SMD Dominates)
International: Littelfuse, Bourns, TDK, Vishay
Taiwan: PTTC, Polytronics
China: TLC, KET, Huade, Sunloong

Bourns Ptc Resettable Fuses

Bourns’ Multifuse® PPTC resettable fuses are among the most widely used and reliable brands globally, with particularly extensive applications in SMD, automotive, high-temperature, and USB/Type-C protection. Bourns, Inc. provides the following comprehensive, practical, and ready-to-use specifications.

I. Brand and Positioning
Brand: Bourns (U.S.), a global leader in circuit protection
Product Line: Multifuse® PPTC (Polymer Positive Temperature Coefficient Resettable Fuse)
Advantages:
Full range of SMD (0402–2920) + through-hole packages
Comprehensive coverage of automotive-grade AEC-Q200, industrial-grade, and high-temperature 125°C applications
Complete certifications: UL, CSA, TÜV, RoHS, halogen-free
Stable, low internal resistance, fast recovery, long service life

II. Core Series (Most Commonly Used)
1. General-purpose consumer electronics SMD: MF-MSMF Series (Most Popular)
Package: 0603 / 0805 / 1206 / 1812
Vmax: 6V / 16V / 24V / 30V / 60V (Latest Expansion in 2025)
Ihold: 0.05A–3.0A (35 new models added in 2025, up to 3A)
Technology: freeXpansion™, higher current, more stable resistance
Applications: USB-A/C, Type-C, mobile phones / tablets / laptops, cameras, LEDs, sensors
Typical Models:
MF-MSMF050-2: 0.5A / 30V / 0805
MF-MSMF110-2: 1.1A / 30V / 1206
MF-MSMF260-2: 2.6A / 30V / 1812
MF-MSMF300-2: 3.0A / 30V / 1812 (Latest)

2. Automotive-grade AEC-Q200: MF-RG / MF-USHT / MF-MSHT Series
MF-RG (Through-hole Radial): 16V, Ihold 3A/4A/5A, AEC-Q200, Automotive Electronics
MF-USHT (SMD 1210): 36V, Ihold up to 2A, 125°C, AEC-Q200
MF-MSHT (SMD 1812): 42V, Ihold up to 1.75A, 125°C, AEC-Q200 Bourns, Inc.
Applications: Automotive BCU, ECU, vehicle lighting, sensors, in-vehicle USB

3. High-Temperature Industrial Grade (-40°C to +125°C): MF-FSHT / MF-PSHT / MF-NSHT
Package: 0603 / 0805 / 1206
Vmax: 12V–16V
Ihold: 0.05A–0.75A
Certifications: UL/CSA/TÜV, AEC-Q200, RoHS Bourns, Inc.
Applications: Industrial control, motor drives, data storage, outdoor equipment

III. Key Parameters (Essential for Selection)
Ihold (Hold Current): Current at which the device remains inactive at room temperature; must be ≥ 1.2–1.5 times the operating current
Itrip (Trip Current): ≈ 2×Ihold; protection activates upon overcurrent
Vmax (Maximum Withstand Voltage): Must be ≥ the circuit’s maximum voltage (including surges)
R0 (Initial Resistance): mΩ–Ω range; lower is better (lower voltage drop, lower power consumption)
Operating Temperature: Consumer grade 0–85°C; Industrial / Automotive grade –40–+125°C
Package: Higher current → Larger package (0603 → 0805 → 1206 → 1812)

IV. Selection Steps (Official Recommendation by Bourns)
Determine circuit voltage → Select Vmax ≥ operating voltage
Determine maximum operating current → Select Ihold ≥ operating current × 1.2–1.5
Determine ambient temperature → Select the 125°C series (MF-USHT/MSHT) for high-temperature applications
Determine package → Select 0603/0805 for limited space; select 1206/1812 for high current
Determine certification → Select AEC-Q200 for automotive; select UL/CSA/TÜV for industrial

Polymer Ptc Resettable Fuse

Polymer PTC Resettable Fuse

I. Full Name
Polymer Positive Temperature Coefficient
Abbreviation: PPTC
Chinese: Polymer Positive Temperature Coefficient Thermistor / Self-Resetting Fuse

II. Basic Structure
Matrix: Polymer (polyethylene-based)
Filler: Conductive carbon black particles
Structure: In the crystalline state of the polymer, conductive particles are uniformly distributed to form a conductive path

III. Operating Principle (Standard Explanation)
Normal State (Low Temperature)
The polymer is in a crystalline state, with conductive particles in close contact → Low resistance; current flows normally.
Overcurrent / Overheat Tripping
Excessive current → Heat generation → The polymer melts, expands, and transitions to an amorphous state
→ Conductive particles are pulled apart, breaking the conductive network
→ Resistance instantly increases by a factor of 10⁴ to 10⁶
→ Current is limited to a minimum, providing protection.
Automatic Reset
Fault resolved → Temperature drops → Polymer recrystallizes
→ Conductive particles reconnect → Low-resistance conduction is restored.

IV. Key Features
Automatically resets; no replacement required
Does not fuse or open the circuit during operation; merely limits current
Available in both surface-mount (SMD) and through-hole packages with extremely small dimensions
Suitable for SMT and mass production
Can operate repeatedly for hundreds of thousands of cycles
Low cost, high consistency

V. Polymer PTC vs. Ceramic PTC (Very Important)
Table
Item    Polymer PPTC    Ceramic CPTC
Material    Polymer + Carbon Black    Ceramic Semiconductor
Operating Characteristics    Extreme sudden change in resistance    Gradual increase in resistance
Recovery    Excellent, full recovery    Average, prone to aging
On-resistance    Very low (mΩ range)    Relatively high
Size    Extremely small (SMD 0402 and smaller)    Relatively large
Main Applications    Overcurrent protection (resettable fuse)    Constant-temperature heating, demagnetization, startup
Industry Terminology    Resettable fuse    Constant-temperature PTC, heating PTC
Important: 99% of “resettable fuses” on the market are polymer PPTCs.

VI. Standard Electrical Parameters (General Definitions)
Ihold Holding Current: Maximum current at which the device remains inactive over the long term
Itrip Trip Current: Current that triggers protection (≈2×Ihold)
Vmax Maximum Withstand Voltage: Highest voltage the component can withstand
R1 Initial Resistance: Resistance at room temperature
Rmax Post-Trip Resistance: High resistance in the protected state

VII. Typical Applications (Polymer PPTC Specific)
USB / Type-C port overcurrent protection
Power banks, lithium battery pack protection
Microcontrollers, sensors, module power supplies
Motor stall protection
Automotive electronics (AEC-Q200)
Industrial interfaces, security systems, LED drivers

VIII. Standard Circuit Symbols
plaintext
┌───────────┐
│    ←→     │
──┤           ├──   Polymer PPTC
└───────────┘
Legend: PPTC, PTC, RT

Radial Leaded Ptc Resettable Fuse

Radial-lead (through-hole) PTC resettable fuses (PPTC) are through-hole-mounted polymeric self-resetting overcurrent protection devices suitable for high-current, high-voltage applications and traditional PCB/wiring harness scenarios. They offer superior stability and heat dissipation compared to SMD surface-mount types.

I. Basic Definitions and Structure
Full Name: Radial-lead Polymer Positive Temperature Coefficient Resettable Fuse (Radial Leaded PPTC)
Structure: Square/round epoxy encapsulation + two tin-plated copper leads (through-hole soldering)
Principle: Overcurrent generates heat → Polymer expands → Conductive network breaks → Resistance spikes to limit current; automatically resets upon cooling after fault resolution

II. Key Advantages (Compared to SMD)
Higher current capacity: Withstands currents up to 15A+, suitable for power supplies, motors, and wiring harness protection
Higher voltage rating: Covers 16V/30V/60V/250V/600V, suitable for industrial and utility power applications
Better heat dissipation: Thermal conductivity via leads + air convection, suitable for continuous high-current and high-temperature environments
Flexible installation: Can be directly inserted into PCBs, soldered to wires, or inserted into cables
Easy maintenance/replacement: Through-hole soldering allows for easy removal and replacement

III. Major Brands and Series (Quick Selection Guide)
1. Littelfuse (Most Popular)
30R Series: 30V, Ihold 0.9–9A, suitable for USB and low-voltage devices
Example: 30R160 (Ihold=1.6A, Itrip=3.2A, 30V)
60R Series: 60V, Ihold 0.1–3.75A, industrial / telecommunications
16R Series: 16V, Ihold 2.5–14A, high-current applications
250R Series: 250V, Ihold 0.08–0.18A, mains power / adapters

2. Bourns
MF-RG Series: 16V, Ihold 3–5A, AEC-Q200 automotive grade
MF-NSHT/FSHT: 125°C high-temperature radial, industrial / automotive

3. Eaton
PTR Series: 16V/30V/60V, Ihold 0.1–15A, low-resistance fast-acting

4. Domestic Brands (Juding, Jinke, Yiding, etc.)
JK Series: 250V/600V, Ihold 0.05–2A, high cost-performance ratio, home appliances / power supplies

IV. Key Selection Parameters (Must Read)
Ihold (Hold Current): Long-term non-triggering current, ≥ operating current × 1.2–1.5
Itrip (Trip Current): ≈2×Ihold, triggers protection
Vmax (Maximum Withstand Voltage): Must be ≥ the circuit’s maximum voltage (including surges)
R0 (Initial Resistance): mΩ–Ω range, lower is better (lower voltage drop, lower power consumption)
Maximum Fault Current: Short-circuit current it can withstand (typically 40–100A)
Operating Temperature: -40°C to +85°C (Industrial / Automotive grade up to 125°C)

V. Typical Packages and Dimensions
Square: 7×4×5 mm, 10×5×6 mm (most common)
Round (disc-type): φ12×3 mm, pin pitch 5.1 mm
Pins: Tinned copper, wire gauge 0.5–0.8 mm, suitable for PCB through-hole soldering

VI. Typical Applications
Power adapters, chargers, switching power supplies (250V series)
Motor stall protection, industrial control boards (16V/30V high current)
Automotive electronics (AEC-Q200 automotive grade)
USB/Type-C ports, battery packs, security equipment
Home appliances, communication equipment, LED drivers

VII. Circuit Symbols and Wiring
Symbol: Rectangle + double-headed arrow (PPTC)
Wiring: Connected in series in the positive current path
plaintext
VCC → Radial PPTC → Load → GND
Part Numbers: RTxx, PPTCxx, Fxx

VIII. Selection Steps
Determine circuit voltage → Select Vmax ≥ operating voltage
Determine maximum operating current → Select Ihold ≥ operating current × 1.2–1.5
Determine ambient temperature → Select the 125°C series for high-temperature applications
Determine mounting method → Select square/round for through-hole PCB; select lead-welding for wire harnesses
Determine certification → Select AEC-Q200 for automotive; select UL/CSA for industrial