with video of polyfuse

1. POLYFUSE
By
Chaitanya Pendyala

2. Contents
Introduction
Construction
Principle of operation
Operating Parameters
Types
Applications
Conclusion

3. Introduction
Basically a Thermistor
It is re-settable by itself.
Polymeric positive temperature coefficient thermistors (PPTC).
A new standard for circuit protection.
A series element in a circuit.

4. Construction
Made from a composite of semi-crystalline polymer & conductive particles.
Comprises thin sheets of conductive plastic with electrodes attached to either side.
The device resistance rises with temperature.
Fuses provide over current protection & automatic restoration.
Voltage rating 30 to 250 volts.
Current rating 20mA to 100A.

5. Over current protection
• Polyfuse is a series element in a circuit.
• PPTC device protects the circuit by going from a low-resistance to high-
resistance state in response to an over current protection.

6. • In normal operation the device has a resistance that is much lower
than the remainder of the circuit.
• In response to an overcurrent condition, the device increases in
resistance (trips)
• Reducing the current in the circuit to a value that can be safely
carried by any of the circuit elements.
• Due to rapid increase in the temperature of the device, caused by
I2R heating.

7. Practical test on Polyfuse

8. 01

9. 02

10. 03

11. 04

12. 05

13. 06

14. 07

15. 08

16. Principle of Operation
• In case of excessive current flows through the
device, the temperature of conductive
material arises.
• When temperature exceeds its phase-
transformation temperature, the crystalline
structure changes into an expanded
amorphous state.
• Now the conductive particles move apart from each other.
• The increase in resistance stops flow of current through the device.

17. Operating Parameters
• Initial Resistance: It is the resistance of the device as received from the factory of manufacturing.
• Operating Voltage: Maximum voltage a device can withstand without damage at the rated current.
• Holding Current: Safe current passing through the device under normal operating conditions.
• Trip Current: It is the value of current at which the device interrupts the current.
• Time to Trip: The time it takes for the device to trip at a given temperature.
• Tripped State: Transition from the low resistance state to the high resistance state due to an overload.
• Leakage Current: A small value of stray current flowing through the device after it has switched to
high resistance mode.
• Trip Cycle: The number of trip cycles (at rated voltage & current) the device sustains without failure.
• Trip Endurance: The duration of time the device sustains its maximum rated voltage in the tripped
state without failure.
• Power Dissipation: Power dissipated by the device in its tripped state.
• Thermal Duration: Influence of ambient temperature.
• Hysteresis: Period b/w the actual beginning of the signaling of the device to trip & the actual tripping
of the device.

18. Types

19. Surface mount re-settable Fuses
Radial ledded re-settable fuses
Battery strap re-settable fuses

20. Polyfuses in Market

21. Applications
• Transformer protection
• Speaker protection
• Battery protection
• IC protection
• Protection of electrical equipments & computer peripherals
• Automobiles
• Lighting, Security & Fire alarm system

22. Conclusion
• Self Resettable device
• Low Resistance
• Fast trip time
• Ideal for low cost over current protection
• Ideal for low voltage

23. Thankyou
for your attention

24. Q ?