PolySwitch® Resettable Devices

Littelfuse PolySwitch and POLY-FUSE devices are Polymeric Positive Temperature Coefficient (PPTC) devices which offer a resettable overcurrent protection alternative, thereby reducing warranty, service and repair costs. Ideal for situations where frequent overcurrent conditions occur or constant uptime is required, resettable PPTCs are typically used in consumer electronics, power line, telecom, I/O port, process control and medical equipment protection applications.

PPTCs increase resistance as temperature increases due to increased flow. Designed to limit unsafe currents while allowing constant safe current levels, resistance will "reset" automatically when the fault is removed and temperature returns to a safe levels.

Surface mount resettable PPTC devices provide overcurrent protection for applications where space is at a premium and resettable protection is desired. Package size varies from 0402 to 3425, while hold current ranges from 50mA to 7.0A. LoRho0603L, 0805L, 1206L, 1210L, 1812L, 2016L, 2920L, 250S, femtoSMD, picoSMD, nanoSMD, microSMD, miniSMD, decaSMD, SMDC, AHS, SMD, nanoAMSD, microASMD, miniASMD, ASMD.

Radial leaded resettable PPTCs are designed to provide overcurrent protection for applications where space is not a concern and resettable protection is preferred. USBR, 16R, 30R, 60R, 72R, 250R, 600R, RGEF, RUEF, RXEF, RHEF, RKEF, AGRF, AHRF, AHEF.

Battery strap resettable PPTCs provide reliable, non-cycling protection against overcharging and short circuits events for rechargeable battery cells where resettable protection is desired. VLR, VLP, VTP, MXP, MGP, SRP, LR4, RSD.

New Littelfuse Lo Rho resettable PPTCs offers ultra-low normal operating resistance while maintaining the same performance of other Littelfuse PPTC products and are available in Surface Mount Low Rho SMD Series and Surface Mount Lo Rho Series.

The Telecom resettable PPTC Series is designed to protect against short-duration high-voltage fault currents (power cross or power induction surge) typically found in telecommunications and networking applications. The 250R, 250S, TRF250, TSL250, TS250, TCF250 and TSV250 series can be used to help telecom networking equipment meet the protection requirements specified in ITU K.20 and K.21. The 600R, TRF600, TR600, TS600 and TSM600 series is designed to be used in applications that need to meet the requirements of GR–1089-CORE and UL60950/ EN60950/IEC60950.

Littelfuse plants for PolySwitch devices are ISO/TS 16949:2009 and ISO 9001:2008 certified.

Traditional Fuses vs. PPTCs

Fuses and PPTCs are both overcurrent protection devices, though each offer their own unique operating characteristics and benefits. Understanding the differences between the two technologies should make the choice in selection easier, depending on the application.

The most obvious difference is that PPTCs are automatically resettable whereas traditional Fuses need to be replaced after they they are tripped. Whereas a fuse will completely stop the flow of current (which may be desired in critical applications) after most similar overcurrent event, PPTCs continue to enable the equipment to function, except in extreme cases.

Because they reset automatically, many circuit designers choose PPTCs in instances where overcurrent events are expected to occur often, and where maintaining low warranty and service costs, constant system uptime, and/or user transparency are at a premium. They are also often chosen in circuits that are difficult to access or in remote locations, were fuse replacement would be difficult.

There are several other operating characteristics to be considered that distinguish PPTCs and fuses, and it is also best to test and verify device performance before use within the end application.

To learn more about traditional fuses versus PPTCs click here.

PPTC Characteristics and Terms

Overcurrent circuit protection can be accomplished with the use of either a traditional fuse or PPTC (positive temperature coefficient) device. PPTCs are typically used in a wide variety of telecom, computer, consumer electronics, battery and medical electronics product applications where overcurrent events are common and automatic resettability desired.

Littelfuse offers PPTCs with the following general forms and features, and come in a variety of sizes and capacities:

Surface Mount Devices:

  • A full range of compact footprints
  • Low hold current
  • Very fast trip time
  • Low resistance

Radial Leaded Series:

  • Protection devices up to 600Vdc
  • A very high hold current
  • Low trip-to-hold current ratio
  • Low resistance

Battery Strap Devices:

  • A narrow low profile design
  • A weldable band Nickel terminal
  • Low resistance–for extended battery run time

If your application requirements fall outside of our product range, in certain instances we can offer customized solutions. Please contact Littelfuse for more information.

Littelfuse PPTC Characteristics

Both Polymeric (Positive Temperature Coefficient) PPTC and traditional Fuse devices react to heat generated by the excessive current flow in a circuit. A fuse melts open, interrupting the current flow whereas a PPTC limits current flow as it rises in temperature, changing from low to high resistance state. In both cases this condition is called "tripping." The graph at right shows the typical response of a PPTC to temperature.

Littelfuse Polymer PPTCs are made chiefly of high density polyethylene mixed with graphite. During an overcurrent event, a Polymer PPTC will heat and expand, which in turn causes the conducting particles to break contact and stop the current.

The general procedure for resetting the device after an overload has occurred is to remove power and allow the device to cool down.

Leakage Current

When a PPTC is in a "tripped state" it protects the circuitry by limiting the current flow to a low leakage level. Leakage current can range from less than a hundred milliamps (mA) at rated voltage up to a few hundred milliamps (mA) at lower voltages. Fuses on the other hand completely interrupt the current flow when tripped, and this open circuit results in no leakage current when subjected to an overload current.

Interrupting Rating

PPTCs are rated for a maximum short circuit current at rated voltage also known as "breaking capacity" or Imax. This fault current level is the maximum current that the device can withstand safely, keeping in mind that the PPTC will not actually interrupt the current flow (see Leakage Current above). A typical Littelfuse PPTC short circuit rating is 40A; or for the battery strap PPTCs, this value can reach 100A. Fuses do in fact interrupt the current flow in response to the overload and the range of interrupting ratings, vary from tens of amperes (A) up to 10,000 (A) amperes at rated voltage.

Operating Voltage Rating

General use Littelfuse PPTCs are not rated above 60V while fuses are rated up to 600V.

Hold Current Rating

The hold (operating) current rating for PPTCs can be up to 14A, while the maximum level for fuses can exceed 30A.


Reviewing product specifications indicates that similarly rated PPTCs have about twice (sometimes more) the resistance of fuses.

Agency Approvals

Littelfuse PPTCs are Recognized under the Component Program of Underwriters Laboratories to UL Standard 1434 for Thermistors. The devices have also been certified under the CSA Component Acceptance Program.

Time-Current Characteristic

Comparing the time-current curves of PPTCs to time-current curves of fuses show that the speed of response for a PPTC is similar to the time delay of a Littelfuse Slo-Blo® fuse.

Temperature Rerating

The useful upper limit for a PPTC is generally 85°C, while the maximum operating temperature for fuses is 125°C.

Ambient temperature effects are in addition to the normal rerating. PPTCs hold and trip rating must be rerated when applied at conditions other than room ambient. For example, any rise in ambient temperature will decrease the hold current rating as well as the trip current. A reduction in ambient temperature will increase the trip current as well as the hold current.

The temperature rerating curves in the table below compare PPTCs to fuses and illustrate that more rerating is required for a PPTC at a given temperature.

Temperature Rerating Curves Comparing PPTCs to Fuses

Chart Key Temperature-Rerating-Curves-Comparing-PTCs-to-Fuses
Curve A
Thin-Film Fuses and 313 Series (.010 to .150A)

Curve B
FLAT-PAK® , Nano2® , PICO® , Blade Terminal,
Special Purpose and other leaded and cartridge fuses
(except 313.010 – .150A)

Curve C
Resettable PPTCs

PPTCs are typically used as circuit protection in applications where sensitive components are at constant risk of damage from overcurrent conditions. The ability of PPTCs to reset themselves after exposure to a fault current makes them ideal within circuits that are not easily accessible to a user or technician or where constant uptime is required.

Typical applications include port protection on personal computers (USB, Firewire, keyboard/mouse, and serial ports), peripherals (hard drives, video cards, and hubs), cell phone, battery packs, industrial controls, lighting ballast and motor controls.

The chart below is meant as a quick guide in narrowing to a Littelfuse PPTC device that may be appropriate to certain end applications.

For detailed application assistance please visit our Application Design Center Site.

LoRho 0603L 0805L 1206L 1210L 1812L 2016L 2920L 250S
Ul60950 ,TIA-968-A, GR-1089 Req's
ITU-T Recoomendations
CPE (Customer Premises Equipment)
Analog Line Card
T1/E1/J1 And HDSL
Cable Telephony
PBX/KTS And Key Telephone System
Computer CPU
IEEE1284 Parallel Data Bus
IEEE 802.3
IEEE 1394
I/O Ports
PC Card
Video Port
HDMI / LCD Monitor
Set Top Box
Smart Card Reader
Mobile Phone
Linear AC/DC Adapter
Portable Electronic Input Port
Electromagnetic Loads, Motor
Solenoid Protection
Voltage / Current Input Terminal
USBR 16R 30R 60R 72R 250R 600R LR LT SL ST VL VT
Battery Lithium Cell
Battery Pack
Ul60950 ,TIA-968-A, GR-1089 Req's
ITU-T Recoomendations
CPE (Customer Premises Equipment)
Analog Line Card
T1/E1/J1 And HDSL
Cable Telephony
PBX/KTS And Key Telephone System
Computer CPU
IEEE1284 Parallel Data Bus
IEEE 802.3
IEEE 1394
I/O Ports
PC Card
Video Port
LCD Monitor
Consumer Electronics
Linear AC/DC Adapter
Electromagnetic Loads, Motor
Solenoid Protection

Note: The application summary is for reference only. Determination of suitability for a specific application is the responsibility of the customer.

Typical PPTC Circuit Protection Designs

The following are examples of typical circuits using Littelfuse PPTCs in combination with other Littelfuse circuit protection devices to provide a comprehensive protection solution. Contact a Littelfuse application expert for design assistance or visit www.littelfuse.com/designcenteror https://www.littelfuse.com/PPTCs for additional information. Be sure to to verify specifications and test device performance before use in the end application.

Power Over Ethernet


LI-ION Battery Pack


USB 1.1


USB 2.0


IEEE 1394 - Firewire


TIP/Ring Circuit - Metallic


PPTC Selection Worksheet

  1. Define the circuit operating parameters

    Normal operating current in amperes:


    Normal operating voltage in volts:


    Maximum interrupt current:


    Ambient temperature:


    Typical overload current:


    Required opening time at specified overload:


    Transient pulses expected:


    Agency approvals:


    Mounting type/form factor:


    Typical resistance (in circuit):

  2. Select the proper circuit protection component.

    (Refer to PPTC Selection Tables below and specifications with Data Sheets)

  3. Determine the opening time at fault.

    Consult the Time-Current (T-C) Curve of each PPTC series to determine if the selected part will operate within the constraints of your application.

    If the device opens too soon, the application may experience nuisance operation. If the device does not open soon enough, the overcurrent may damage downstream components.

    To determine the opening time for the chosen device, locate the overload current on the X-axis of the appropriate T-C Curve and follow its line up to its intersection with the curve. At this point read the time tested on the Y-axis. This is the average opening time for that device.

    If your overload current falls to the right of the curve the device will open. If the overload current is to the left of the curve, the device will not operate.

  4. Verify ambient operating parameters.

    Ensure that the application voltage is less than or equal to the device's rated voltage and that the operating temperature limits are within those specified by the device.

  5. Verify the device's dimensions.

    Compare the maximum dimensions of the device to the space available in the application. The dimension of each product is included within each data sheets on the following pages.

  6. Test the selected product in an actual application.

PPTC Selection Tables

Type Surface Mount
Series 0603L 0805L 1206L 1210L 1812L 2016L 2920L 250S
Chip Size 0603 (1608) 0805 (2012) 1206 (3216) 1210 (3225) 1812 (4532) 2016 (5041) 2920 (7351)  
Hold Current (IHOLD) 0.10 - 0.35 A 0.10 - 1.00 A 0.125 - 1.50 A 0.05 - 1.50 A 0.10 - 2.60 A 0.30 - 2.00 A 0.30 - 3.00 A 0.13A
Max Voltage (VMAX) 6 –15 V 6 –15 V 6 – 30 V 6 – 30 V 6 – 60 V 6 – 60 V 6 – 60 V 60 V
Max Fault Current (IMAX) 40 A 40 / 100 A 100 A 10 / 100 A 10 / 20 / 100 A 20 / 40 A 10 / 40 A 3 A
Operating Temperature Range -40ºC to 85ºC
Agency Approval PTC-Surface-Mount-Agency-Approval PTC-Surface-Mount-Agency-Approval PTC-Surface-Mount-Agency-Approval
RoHS Compliant
Type Radial Leaded
Series USBR 16R 30R 60R 72R 250R 600R
Hold Current (IHOLD) 0.75 - 2.50 A 2.50 - 14.00 A 0.90 - 9.00 A 0.10 - 3.75 A 0.20 - 3.75 A 0.08 - 0.18 A 0.15 - 0.16 A
Max Voltage (VMAX) 6 / 16 V 16 V 30 V 60 V 72 V 60 / 250 V 60 / 600 V
Max Fault Current (IMAX) 40 A 100 A 40 A 40 A 40 A 3 / 10 A 3 A
Operating Temperature Range -40ºC to 85ºC
Agency Approval PTC-Radial-Leaded-Agency-Approval PTC-Radial-Leaded-Agency-Approval
RoHS Compliant
Type Battery Strap
Hold Current (IHOLD) 1.90 - 7.30 A 0.70 - 3.40 A 1.20 - 1.75 A 1.70 - 2.30 A 1.70 - 2.40 A
Max Voltage (VMAX) 15 / 20 V 15 / 24V 15 V 12 V 16 V
Max Fault Current (IMAX) 100A
Operating Temperature Range -40ºC to 85ºC
Agency Approval PTC-Battery-Strap-Agency-Approval PTC-Battery-Strap-Agency-Approval
RoHS Compliant

pdf icon Data Center Solutions Selection Guide

Today’s datacenters must handle the vastly higher volumes of data being produced by millions of mobile devices and the objects that make up the Internet of Things

EC606 Protecting the Universal Serial Bus from Over Voltage and Overcurrent Threats

This application note addresses the various requirements for protecting the Universal Serial Bus (USB) from overcurrent and over voltage environmental threats.The solutions presented cover both USB 1.1 and the higher speed USB 2.0 circuitry.

EC616 Circuit Protection of USB 2 0

This application brief demonstrates how to ensure reliable and safe circuit operation of USB products, protection against voltage and current transients must be carefully considered. Due to the higher data rates of USB 2.0, attention to the electrical characteristics of protection solutions is required.

pdf icon Automotive Devices Quick Reference Application Guide


pdf icon Light Emitting Diode LED Lighting Applications Quick Reference Application Guide

pdf icon Circuit Protection Portfolio Quick Reference for Connectors and Protection Application Guide

pdf icon Portable Medical Devices Protection Quick Reference Application Guide

pdficon Protecting Rechargeable Li ion and Li Polymer Batteries in Consumer Electronics Application Note

pdf icon Circuit Protection Solution for Lithium Cells Application Note

pdf icon Techniques for Protecting Smart Sweeping Robots Application Note

pdf icon Using PolySwitch PPTC Devices for LPS Compliance in Li_ion and LiP Cell Battery Application Note

pdf icon MSL Classification Product Brochure


pdf icon PolySwitch Device Selection Guide Product Brochure

pdf icon Fundamentals of Resettable Functionality in PPTC Devices Technical Paper

pdf icon PolySwitch Mini terminal Bladed Device Helps Protect Automotive Technical Paper

pdf icon The Birth of a Safety Standard The IEC 62368_1 Technical Paper

pdf icon POLY-FUSE® and PolySwitch® SMD PPTC Application Note