Polyfuse

SEMINARON

MULTI-FUSE

By : SHUBHAM VERMA

B.E. IV YEAR

MULTI-FUSE

CONTENT :

• INTRODUCTION

• OVER-CURRENT PROTECTION

• CONSTRUCTION AND OPERATION

• PRINCIPLE OF OPERATION

• OPERATING PARAMETERS

• DIFFERENT TYPES OF POLYFUSE

• ADVANTAGES OVER CONVENTIONAL FUSES

• APPLICATION

• CONCLUSION

• REFERENCE

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.

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.

CONSTRUCTION AND OPERATIONPPTC 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:

II. AMORPHOUS PHASE :

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.

OPERATING PARAMETERS Initial Resistance

· Operating Voltage

· Holding Current

· Trip Current

· Time to Trip

· Tripped State

· Leakage Current

· Trip Cycle

· Trip Endurance

· Power Dissipation

· Hysteresis

DIFFERENT TYPES OF POLYFUSE

• Surface Mount Resettable Fuses :

2. Radial-Leaded Resettable Fuses :

3.Battery Strap Resettable Fuses :

ADVANTAGES OVER CONVENTIONAL FUSES1. 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

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

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.

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