18-02-2010, 01:32 PM
[attachment=2344]
RESETTABLE FUSE
Electrical fuse
Various fuses
¢ Thermal fuse
¢ Resettale fuse
Resettable fuse (PPTC)
Positive polymeric temperature coefficient
INTRODUCTION
Ablity to handle higher current and voltage
PPTC effect,secure protection
Current rating
MANUFACTURE
PPTC consist of multiple top and bottom layer, made of non crystalline organic polymer with conducting materials, carbon black particles
APPLIED PRINCIPLE resettable fuse the new type over current protection products with the double functions as
Overcurrent protection
Automatic restoration
OVERCURRENT PROTECTION
in case of short circuit or unusually high current, the self-heating of PPTC may make its impedance increasing to limit very low current pass through
it so playing the role for protecting current.
Automatic restoration
When high current appears, PPTC temperature rapidly rise and polymer will expand and lead to conducting passage breaking, thus resulting impedance rising the passing current is low and the circuit being break off and achieving goal of protection.
when unusually high current disappears the self heating PPTC will not be enough to maintain its high resistance state so impedance turn to low resistance
Working principle
While cool, the polymer in crystalline state , forming many conductive chains
If too much current is passed ,called trip current, the device will begin to heat
As the device heats it changes to its non crystalline state
Then the polymer become expand, this separates the carbon particle and breaks the conductive pathways ,causing the resistance to increase
This resistance reduce the current in the circuit ,the current maintain the temperature and keep at the high resistance level
When faults are removed pptc will cool and come to its original shape, it can hold the current
Characteristics of restoring time
Within some seconds, the temperature of PPTC component will drop soon and it will rapidly reset itself into the low resistance state.
Effect of ambient temperature
Below 20°C current passing the resettable fuse dropping
at 20°C, 100 percent of current passing
Above 20°C, the larger the passing current and the shorter the operating time.
Advantages
Compared to ordinary fuse ,it possess “little volume
-solidness
The reset time be 20s
will provide outstanding protection from a potentially hazardous overcurrent
DISADVANTAGES
Avoid contact of device with chemical solvent
Operation beyond specified maximum rating results damage
Applications
Computers power supplies
Rechargeable battery packs
CONCLUSION
Resettable fuse technologies have been associated with very costly top secure application
RESETTABLE FUSE
Electrical fuse
Various fuses
¢ Thermal fuse
¢ Resettale fuse
Resettable fuse (PPTC)
Positive polymeric temperature coefficient
INTRODUCTION
Ablity to handle higher current and voltage
PPTC effect,secure protection
Current rating
MANUFACTURE
PPTC consist of multiple top and bottom layer, made of non crystalline organic polymer with conducting materials, carbon black particles
APPLIED PRINCIPLE resettable fuse the new type over current protection products with the double functions as
Overcurrent protection
Automatic restoration
OVERCURRENT PROTECTION
in case of short circuit or unusually high current, the self-heating of PPTC may make its impedance increasing to limit very low current pass through
it so playing the role for protecting current.
Automatic restoration
When high current appears, PPTC temperature rapidly rise and polymer will expand and lead to conducting passage breaking, thus resulting impedance rising the passing current is low and the circuit being break off and achieving goal of protection.
when unusually high current disappears the self heating PPTC will not be enough to maintain its high resistance state so impedance turn to low resistance
Working principle
While cool, the polymer in crystalline state , forming many conductive chains
If too much current is passed ,called trip current, the device will begin to heat
As the device heats it changes to its non crystalline state
Then the polymer become expand, this separates the carbon particle and breaks the conductive pathways ,causing the resistance to increase
This resistance reduce the current in the circuit ,the current maintain the temperature and keep at the high resistance level
When faults are removed pptc will cool and come to its original shape, it can hold the current
Characteristics of restoring time
Within some seconds, the temperature of PPTC component will drop soon and it will rapidly reset itself into the low resistance state.
Effect of ambient temperature
Below 20°C current passing the resettable fuse dropping
at 20°C, 100 percent of current passing
Above 20°C, the larger the passing current and the shorter the operating time.
Advantages
Compared to ordinary fuse ,it possess “little volume
-solidness
The reset time be 20s
will provide outstanding protection from a potentially hazardous overcurrent
DISADVANTAGES
Avoid contact of device with chemical solvent
Operation beyond specified maximum rating results damage
Applications
Computers power supplies
Rechargeable battery packs
CONCLUSION
Resettable fuse technologies have been associated with very costly top secure application