2. Content
Introduction
Over Current Protection
Construction
Principle of Operation
Types of Polyfuses
Edges Over Conventional Fuses
Applications of Polyfuse
Conclusion
References
3. INTRODUCTION
Basically a Thermistor
Polymeric Positive Temperature Coefficient (PPTC)
A new standard for circuit protection
Self Resettable
A series element in a circuit
4. Over Current Protection
Polyfuse is a series element in a
circuit. The PPTC device protects
the circuit by going from a low-
resistance to a high-resistance
state in response to an over-
current condition
5. Construction
Polyfuse circuit protection devices are made from a composite
of semi-crystalline polymer and conductive particles. At normal
temperature, the conductive particles form low-resistance
networks in the polymer. However, if the temperature rises above the device’s
switching temperature (Tsw) either from high current through the part or from
an increase in the ambient temperature, the crystallites in the polymer melt
and become amorphous. The increase in volume during melting of the
crystalline phase separates the conductive particles resulting in a large non-
linear increase in the resistance of the device.
7. Operating Characteristics
Typical pair of operating
curves for a PolySwitch
device in still air at 0°C and
75°C. The curves are
different because the heat
required to trip the device
comes both from electrical
I2R heating and from the
device environment.
8. Types of Polyfuses
Surface Mount Resettable Fuses
Radial-Leaded Resettable Fuses
Battery Strap Resettable Fuses
9. Edges Over Conventional Fuses
Over current protection
Low base resistance
Latching operation
Automatic resettability
Short time to trip
No arching during faulty situations
Small dimensions and compact designs
Internationally standardized and approved.
No accidental hot plugging
Withstand mechanical shocks and vibrations
Life time- up to 10 times longer
10. Item PPTC CPTC Bi-Metal Fuse
Resettable Yes Yes Yes No
Size Small Medium Large Large
Warranty
Cost
Low Low High High
Power Loss Low High Low Low
Resistance Low High Low Low
Comparison between PPTC and Other Types of Fuses
11. Applications of Polyfuse
Speaker Protection
Battery Protection
IC Protection
Protection of Electrical Equipments
Protection Device Inside Consumer Electronics
Protection of Computer Peripherals
Automobiles, Industrial Control
Medical Electronics
Lighting, Security & Fire Alarm System
Tele Communication Equipment
