0811013118

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POLYMERIC POSITIVE TEMPERATURE

COEFFICIENT DEVICES(PPTC)

-Sulagna Das

ITER, SOA UNIVERSITY

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WHAT IS A PPTC DEVICE ???

It protects against overcurrent surges and overtemperature

faults.

These devices limit the flow of dangerously high current

during fault conditions.

It is a polyswitch which resets after fault is cleared and power

is removed hence reduces warranty, service and repair cost.

It is a passive component that is a nonlinear thermistor andalso acts like a circuit breaker.

It is a low resistance device.

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……….CONTINUE

The latest generation of PPTC devices includes components

that are rated for line voltages of 120 VAC and 240 VAC and

can be used in parallel for increased current capacity.

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PARAMETERS Initial resistance: The resistance of the device as received from the

factory of manufacturing.

Operating voltage: The maximum voltage a device can withstand

without damage at the rated current. Holding current : Safe current through the device.

Trip current : Where the device interrupts the current.

Time to trip: The time it takes for the device to trip at a giventemperature.

Tripped state: Transition from the low resistance state to the highresistance state due to an overload.

Leakage current : A small value of stray current flowing through thedevice after it has switched to high resistance mode.

Trip cycle: The number of trip cycles (at rated voltage and 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: The range between where the device trips and where thedevice returns to a conductive state.

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HOW DOES IT WORK???? PPTC device, i.e a series element in the circuit comprises of a

non-conductive crystalline organic polymer matrix that isloaded with carbon black to make it conductive.

At normal temperature, the polymer is in a crystalline state.

It passes a given current, called the "hold current".

If too much current is passed through the device, i.e “ tripcurrent", the device will begin to heat above the switchingtemperature(Tsw). Hence , polymer will expand, changingfrom a crystalline to an amorphous state.

Carbon particles separates and breaks the conductivepathways, and resistance increases several orders ofmagnitude nonlinearly(generally hundreds and thousands of

ohms). This increase in resistance reduces the current to a value that

can be safely carried by any of the circuit elements.

The critical material, which is a carbon black and plastic mix,are used in the automatically resetting devices.

http://en.wikipedia.org/wiki/Carbon_black

http://en.wikipedia.org/wiki/Amorphous

http://en.wikipedia.org/wiki/Amorphous

http://en.wikipedia.org/wiki/Carbon_black

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•When the power and fault are removed, 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.

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CHARACTERISTIC CURVES

Point 1 &2 are at normal condition, heat

generated is balanced with heat lost at

low temperature.

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.

Hence it causes the device to

generate heat at a rate greater than

the rate at which heat can be

dissipated, thus causing the device to

heat up rapidly and increase inresistance(point 3 to4)for a very small

change in temperature.

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………..CONTINUE

As long as the applied voltage remains at this level, the

device will remain in the tripped state . Once the voltage

decreases, the power is removed, and the device cools, thedevice will reset automatically.

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CURRENT VS TIME GRAPH

At 75°C the heat input from the

environment is substantially greater

than it is at 0°C,

Additional I2R needed to trip the

device is less, resulting in a lower

trip current at a given trip time (or a

faster trip at given trip current).

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APPLICATIONS

Battery protection(Cell phone,MP3 player, DSC’s)

IC protection

Protection of electrical equipments

Used in computer power supply due to PC97 standard(USB

Ports ,Firework ports , Disk drives)

Used in aerospace/nuclear application

Protecting audio speaker

Automotive electronics( Secutirysystem, Solenoid)

Telecommunication equipments( Faxes, Modem)

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• AUTOMOTIVE APPLICATION

Protective devices that can be located

strategically throughout the vehicle can

help

reduce wire harness size and weight

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• DC INPUT PORT PROTECTION

PolySwitch SMD device

Secondary side protectionSerial Port

PolySwitch LVR device

Primary side protectionPower Supply

ROV

Varistor for Power Supply

Chip fuses

PolySwitch Strap device

Battery PackOvercurrent

& Overtemperature

Protection

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•INDUSTRIAL APPLICATION

Power Management AC Mains

OC Protection

PolySwitch LVR device

Input PowerOV Protection

ROV

Power Driver

Protection

TRIAC, MOSFET, SCR

OC Protection

PolySwitch

LVR/RXE/RUE devices

Comms I/O

OC Protection

PolySwitchRXE, miniSMD

devices

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•PPTC FOR BATTERY PROTECTION

PolySwitch Strap device

Battery Pack

Overcurrent

& Overtemperature

Protection

PolySwitch devices for battery protection

include SRP, LTP, LR4, VTP, VLP, VLR and

MXP series, disc, and special application

strap devices.

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ADVANTAGES

Reduced warranty and service cost.

Protect against overcurrent in circuits and overtemperature in

motors.

Compactness

Increased product reliability

Withstand superior shock and vibration

Wide variety of applications as mentioned earlier. Resettability

Low resistance

Ideal for low voltage AC &DC

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ADVANTAGES OVER OTHER FUSES

DEVICES PPTC CPTC BI-METAL CONVENT-

IONAL

RESETTAB-

LE

YES YES YES NO

SIZE SMALL MEDIUM LARGE LARGE

RESISTAN-

CE

LOW HIGH LOW LOW

POWERLOSS LOW HIGH LOW LOW

COST LOW MEDIUM HIGH HIGH

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ADVANTAGE OF PPTC OVER CPTC

Application of CPTC(ceramic PTC) is limited due to

their relatively high operating temperature , highresistance and large size.

The composition of the CPTC device tends to be

brittle, which makes it vulnerable to damage from

shock, vibration.

In an experiment, two identical transformers were

taken. The PPTC and the CPTC devices were

selected to have the same hold current.

A fault was created with a secondary short, while

current, coil temperature and time-to-trip were

measured.

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The PPTC device exhibited a lower surfacetemperature, resistance, was lower in capacitance

and was less frequency-dependent than the

CPTCdevice.

http://i.cmpnet.com/planetanalog/2009/02/C0362-Figure2.gif

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CONCLUSION

Polymeric positive temperature coefficient device (poly

switch)is a resettable fuse. It is of less cost, small size and of many advantages as

mentioned in previous slides.

It’s applications and differences from other fuses make it very

popular and useful.

Its easy and cheap construction which does not requireextreme conditions add to its quality.

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THANK YOU

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0811013118