This is a full ppt presentation report on polyfuse.

1. SEMINAR
ON
MULTI-FUSE
By : SHUBHAM VERMA
B.E. IV YEAR

2. MULTI-FUSE

3. CONTENT :
• INTRODUCTION
• OVER-CURRENT PROTECTION
• CONSTRUCTION AND OPERATION
• PRINCIPLE OF OPERATION
• OPERATING PARAMETERS
• DIFFERENT TYPES OF POLYFUSE
• ADVANTAGES OVER CONVENTIONAL FUSES
• APPLICATION
• CONCLUSION
• REFERENCE

4. INTRODUCTION
POLYFUSE :A New Standard For Circuit Protection
Fuses work between life and death of a circuitry .
Choosing the right fuse is important for prolonged
protection of the circuitry from over-current and
overvoltage.
Polyfuse is a resettable fuse that doesn’t need to be
replaced like the conventional fuse. Many
manufacturers also call it PolySwitch or MultiFuse.
Polyfuse are designed and made of PPTC material in
thin chip form. It is placed in series to protect a circuit.
Polyfuse provide over-current protection and
automatic restoration.

5. OVER-CURRENT PROTECTION
• Polyfuse is connected in series with protective device.
• The PPTC device protects the circuit by going from a low-
resistance to a high-resistance state in response to an
overcurrent condition , as shown in figure.
• This is known as TRIPPING the device.

6. CONSTRUCTION AND OPERATION
PPTC fuses are constructed with a non-conductive polymer
plastic film that exhibits two phases.
I-Semi crystalline phase II-Amorphous phase
I.SEMI CRYSTALLINE PHASE:

7. II.AMORPHOUS PHASE :

8. PRINCIPLE OF OPERATION
• Polyfuse device operation is based on an overall energy
balance. Under normal operating conditions, the heat
generated by the device and the heat lost by the device to the
environment are in balance at a relatively low temperature, as
shown in Point 1of Figure. If the current through the device is
increased while the ambient temperature is kept constant, the
temperature of the device increases. Further increases in
either current, ambient temperature or both will cause the
device to reach a temperature where the resistance rapidly
increases, as shown in Point 3 of Figure.

9. OPERATING PARAMETERS
 Initial Resistance
· Operating Voltage
· Holding Current
· Trip Current
· Time to Trip
· Tripped State
· Leakage Current
· Trip Cycle
· Trip Endurance
· Power Dissipation
· Hysteresis

10. DIFFERENTTYPESOF POLYFUSE
• Surface Mount Resettable Fuses :

11. 2.Radial-LeadedResettableFuses:
3.Battery Strap Resettable Fuses :

12. ADVANTAGESOVERCONVENTIONAL
FUSES
1. Over current protection
2. Low base resistance
3. Latching operation
4. Automatic resettability
5. Short time to trip
6. No arching during faulty situations
7. Small dimensions and compact designs
8. Internationally standardized and approved
9. No accidental hot plugging
10. Withstand mechanical shocks and vibrations
11. Life time- up to 10 times longer

13. APPLICATIONS
• IN TRANSFORMER PROTECTION
• IN SPEAKER PROTECTION
• IN MOTORS ,FANS AND BLOWERS
• IN INDUSTRIAL PROCESS CONTROL
• IN COMPUTERS
• AUTOMOTIVE SECTORS
• IN AUTOMOTIVE ELECTRONICS
• IN TELECOM SECTORS

14. CONCLUSION
PPTC resettable fuses are designed for today’s demanding
electronic and electrical industries. The concept of a self-
resetting fuse of course predates this technology. Bimetal
fuses, for example are widely used in appliances such as
hairdryers, but these are generally large current devices.
PPTC resettable fuses compete with another common
overcurrent protection device, namely positive
temperature coefficient (PTC) ceramic thermistors.
However, PPTC fuses offer several advantages.
The vast majority PPTC fuses on the market have trip
times in the range 1–10 seconds, but there are PPTC fuses
with trip times of a few milliseconds. Generally speaking,
however, these devices are considered slow-trip fuses. The
blow time depends on the overcurrent, so that a fuse that
may open within a few milliseconds with a severe overload,
may take tens of seconds for a light overload. They are
ideal for all low voltage DC and AC application.

15. REFERENCES
• http://en.wikipedia.org/wiki/poly_fuse
• http://www.seminarsonly.com
• http://www.ieeexplore.com
• http://www.science-direct.com
• http://www.circuitprotection.com
• Electronics For You, Edition- September, 2004
• Raychem circuit protection products- Tyco Electronics