POLY FUSE
INTRODUCTION
 A Polymeric positive temperature co-efficiant device.
 A New standard for circuit protection.
 Basically ...
Over Current Protection
 Polyfuse is a series element in a circuit. The PPTC
device protects the circuit by going from a ...
 When the current flowing through the device
(which has a small resistance in the on state)
exceeds the current limit, th...
Construction
 A Polymeric PTC device comprises a
non-conductive crystalline organic
polymer matrix that is loaded
with ca...
Operation
 Since the crystaline-carbon system is conductivet will pass a
given current, called the "hold current". If too...
 A small current still flows through the device and is
sufficient to maintain the temperature at a level
which will keep ...
 The resetting will often not take place even if the
fault alone has been removed with the power still
flowing as the ope...
 it will most likely stabilize at a significantly higher
resistance (up to 4 times initial value).
Typical Resistance Recovery after a
Trip Event
Figure shows typical behavior
of a PolySwitch device that is
tripped and th...
 Initial Resistance: The resistance of the device as
received from the factory
 Operating Voltage: The maximum voltage a...
Applications
 Poly fuses are used where the replacing of the
fuse is difficult or in the circuit which trips
often
 Prot...
Advantages
 Low base resistance
 Automatic reset ability
 Lack of arcing during faulty conditions
 Less time to trip
...
Reference
 http://en.wikipedia.org/wiki/Resettable_f
use
 http://electronics.stackexchange.com/ta
gs/polyfuse/info
 Ele...
END
DOUBTS?
-Polyfuse
-Polyfuse
Upcoming SlideShare
Loading in …5
×

-Polyfuse

1,266 views

Published on

polyfuse

Published in: Education
0 Comments
5 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
1,266
On SlideShare
0
From Embeds
0
Number of Embeds
4
Actions
Shares
0
Downloads
193
Comments
0
Likes
5
Embeds 0
No embeds

No notes for slide

-Polyfuse

  1. 1. POLY FUSE
  2. 2. INTRODUCTION  A Polymeric positive temperature co-efficiant device.  A New standard for circuit protection.  Basically a thermistor.  Self resettable.  A series element in the circuit
  3. 3. 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  In normal operation the device has a resistance that is much lower than the remainder of the circuit. In response to an over-current 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.
  4. 4.  When the current flowing through the device (which has a small resistance in the on state) exceeds the current limit, the PPTC device warms up above a threshold temperature and the electrical resistance of the PPTC device suddenly increases several orders of magnitude to a "tripped" state where the resistance will typically be hundreds or thousands of ohms. The current subsequently reduces due to the finite voltage of the power source. The rated trip current can be anywhere from 20 mA to 100 A.
  5. 5. Construction  A Polymeric PTC device comprises a non-conductive crystalline organic polymer matrix that is loaded with carbon black particles to make it conductive. While cool, the polymer is in a crystalline state, with the carbon forced into the regions between crystals, forming many conductive chains.
  6. 6. Operation  Since the crystaline-carbon system is conductivet will pass a given current, called the "hold current". If too much current is passed through the device, the "trip current", the device will begin to heat. 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. 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
  7. 7.  A small current still flows through the device and is sufficient to maintain the temperature at a level which will keep it in the high resistance state  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.
  8. 8.  The resetting will often not take place even if the fault alone has been removed with the power still flowing as the operating current may be above the holding current of the PPTC  The resetting will often not take place even if the fault alone has been removed with the power still flowing as the operating current may be above the holding current of the PPTC
  9. 9.  it will most likely stabilize at a significantly higher resistance (up to 4 times initial value).
  10. 10. Typical Resistance Recovery after 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. 11.  Initial Resistance: The resistance of the device as received from the factory  Operating Voltage: The maximum voltage a device can withstand without damage at rated current  Holding Current: Safe current through the device  Trip Current: The current at which the interrupts the current  Time to Trip: The time it takes for the device to trip at a given temperature and current  Tripped State: Transition from low resistance state to 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 Operating Parameters
  12. 12. Applications  Poly fuses are used where the replacing of the fuse is difficult or in the circuit which trips often  Protection Device Inside Consumer Electronics  Protection of Computer Peripherals  Automobiles, Industrial Control  Tele Communication Equipment  Lighting, Security & Fire Alarm System  Speaker Protection  Aero space shuttles
  13. 13. Advantages  Low base resistance  Automatic reset ability  Lack of arcing during faulty conditions  Less time to trip  Compact design and small dimensions  Internationally approved and standardized  Lifetime almost ten times longer  Survive mechanical vibrations and shocks and comply with safety norms
  14. 14. Reference  http://en.wikipedia.org/wiki/Resettable_f use  http://electronics.stackexchange.com/ta gs/polyfuse/info  Electronics 4 u
  15. 15. END
  16. 16. DOUBTS?

×