presentation of polyfuse

1. SEMINARON
POLYFUSE
SUBMITTED TO:
Mr. KULDEEP
BHARDWAJ
Mr. DINESH TIWARI
SUBMITTED
BY:
SACHIN SINGH
1304620015
EE 3rd YEAR

2. CONTENT
 Introduction
 Construction
 Principle of Operation
 Types of Polyfuses
 Advantage Over Conventional Fuses
 Applications of Polyfuse
 Conclusion

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. 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.
 While cool, the polymer is in a crystalline state, with
the carbon forced into the regions between crystals,
forming many conductive chains.

5.  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
 As the device heats, the polymer will expand, changing
from a crystalline into an amorphous state.
 The expansion separates the carbon particles and
breaks the conductive pathways, causing the resistance
of the device to increase.

7. This will cause the device to heat faster and expand more,
further raising the resistance. This increase in resistance
substantially reduces the current in the circuit.

8.  When power is removed, the heating due to the holding
current will stop and the PPTC device will cool.
 As the device cools, it regains its original crystalline
structure and returns to a low resistance state where it
can hold the current as specified for the device.

9. OPERATING
CHARACTERISTICS

10. Typical Resistance Recoveryafter a Trip Event
Figure shows typical behavior of a PolySwitch device that is
tripped and then allowed to cool.
This figure illustrates how, even after a no. of hours, the device
resistance is still greater than the initial resistance.
Over an extended period of time, device resistance will
continue to fall and will eventually approach initial resistance.

11. OPERATING PARAMETERS
 Initial Resistance
 Operating Voltage
 Holding Current
 Trip Current
 Time to Trip
 Tripped State
 Leakage Current
Power Dissipation

12. HOLDAND TRIP CURRENT AS A FUNCTION
OF TEMPERATURE

13. TYPES OF POLYFUSES
Surface Mount Resettable Fuses
Radial-Leaded Resettable Fuses
Battery Strap Resettable Fuses

14. ADVANTAGE OVER
CONVENTIONAL FUSE
Over current protection.
Low base resistance.
Automatic resettability.
Short time to trip.
No arching during faulty situations.
Small dimensions and compact designs.
Withstand mechanical shocks and vibrations.
Life time- up to 10 times longer.

15. APPLICATION OF POLYFUSE
Speaker Protection
Battery Protection
Transformer protection
Protection of Electrical Equipments
Protection of Computer Peripherals
Automobiles, Industrial Control

16. 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

17. thank
you