1.
Seminar
On
Polyfuse
A
Presented by
HRITIK PANIGRAHI
ELECTRICAL
ENGINEERING
Regd no:F20001002056
Sec:D
Guided by
Padmini Pradhan
BOSE, CUTTACK

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.

6.
Principle of Operation

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

12.
Conclusion
Self Resettable Device
Compact
Low Resistance
Fast Trip Time
Ideal for low cost over current protection
Ideal for Low Voltage A.C & D.C

13.
References
 www.google.com
 www.wikipedia.org
 www.SeminarsTopics.com

14.
Thanks