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Polyfuses are resettable fuse.These are generally positive-temperature coefficient thermistors.The device resistance ri...
Polyfuses are usually packaged in radial, axial, surface-mount, chip, disk, or washer form.The conductive plastic is bas...
• PPTC fuses are constructed with a non-conductive polymer plastic film  that exhibits two phases.• The first phase is a c...
• The polymer is combined with highly conductive carbon.• In the crystalline phase the carbon particles are packed into th...
At room temperature numerous carbonchains form conductive paths through theplastic material.In case an excessive current...
The equipment powered by a transformer get overheateddue to excessive current or short-circuit. A PolyFuse onthe secondary...
Nowadays, in speakers, there are possibilities of damage due to mismatches; forexample, high-power amplifiers coupled with...
Batteries are constantly charged and discharged over theirlife-cycle. Over-charge results in an increase in thetemperature...
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Iprog                                         Ilinear: Linear resistor  mA                 Imax                           ...
 Surface Mount Resettable FusesThis surface mount polyfuse family of polymer of polymer basedresettable fusesprovides rel...
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Low Current Programmed Poly Fuse-    High energy is forcing the             -   Relatively high ohmic     Tungsten seperat...
THANKING EVERYONE FOR YOUR KIND PERUSAL THIS PRESENTATION IS PREPARED BY:       ASANSOL ENGINEERING COLLEGE          ELECT...
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Polyfuse

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Polyfuse

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Polyfuse

  1. 1. 1
  2. 2. Polyfuses are resettable fuse.These are generally positive-temperature coefficient thermistors.The device resistance rises with temperature.These comprise thin sheets of conductive plastic with electrodes attached to either side.These fuses provide over-current protection and automatic restoration.Voltage rating-----3o to 250 volts.Current rating-----20mA to 100A. 2
  3. 3. Polyfuses are usually packaged in radial, axial, surface-mount, chip, disk, or washer form.The conductive plastic is basically a non- conductive crystalline polymer loaded with a highly conductive carbon to make it conductive.PPTC devices limit the flow of dangerously high current during fault conditions.PPTC devices reset after the fault is cleared and the power to the circuit is removed. 3333333322 2222222222 2222222222 33
  4. 4. • PPTC fuses are constructed with a non-conductive polymer plastic film that exhibits two phases.• The first phase is a crystalline or semi-crystalline statewhere the molecules form long chains and arrange in a regular structure.• As the temperature increases the polymer maintains this structure but eventually transitions to an amorphous phase where the molecules are aligned randomly and there is an increase in volume. 4
  5. 5. • The polymer is combined with highly conductive carbon.• In the crystalline phase the carbon particles are packed into the crystalline boundaries and form many conductive paths, and the polymer-carbon combination has a low resistance.• When the temperature falls, the polymer returns to its crystalline structure, the volume decreases, and the carbon particles touch and form conductive paths. 5
  6. 6. At room temperature numerous carbonchains form conductive paths through theplastic material.In case an excessive current flows through thedevice, the temperature of the conductiveplastic material rises.When the temperature exceeds its phase-transformation temperature, the crystallinestructure suddenly changes into an expandedamorphous state.Now the conductive particles move apart fromeach other. A dramatic increase in resistance stops theflow of current through the device.The critical current level at which thishappens is known as the trip current. 6
  7. 7. The equipment powered by a transformer get overheateddue to excessive current or short-circuit. A PolyFuse onthe secondary side of the transformer will protect theequipment against overload. 7
  8. 8. Nowadays, in speakers, there are possibilities of damage due to mismatches; forexample, high-power amplifiers coupled with low-power speakers or a speakercoil driven with a high volume. The protection choices for loudspeaker systemsare limited. Using a PolyFuse in series with the speaker will protect it fromover-current/over-heating damage. Choosing a correct trip -current rated PolyFuse isimportant to match the power level of the speaker. 8
  9. 9. Batteries are constantly charged and discharged over theirlife-cycle. Over-charge results in an increase in thetemperature of the electrolyte. This could cause either a fireor an explosion. PolyFuse can play a vital role in thecharging and discharging cycles of batteries. 9
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  12. 12. Iprog Ilinear: Linear resistor mA Imax characteristics Iheat: Temp. is raising Imelt Imelt: Tungsten Silicide is Imin Ialloy Iheat melting Ilinear Iosc Imax: Maximum current of minimum resistance tprog 0µs 1µs 2µs 3µs Imin: Local current min.Vprog Iosc: Oscillation because of break V Ialloy: No autonomous current pinch off
  13. 13.  Surface Mount Resettable FusesThis surface mount polyfuse family of polymer of polymer basedresettable fusesprovides reliable over current protection for a wide range of products such ascomputer motherboards, USB hubs and ports, CD/DVD drives ,digital cameras and battery packs. Each of these polyfuse series features lowvoltage drops and fast trip times while offering full resettability. This makeseach anideal choice for protection in data com and battery powered applicationswhere momentary surges may occur during interchange of batteries or plug andplay operations.Radial-Leaded Resettable FusesDue to the automatic resetting of the polyfuse, these components are idealforapplications, where temporary fault conditions (eg: during hot plugging)canoccur. The radial-leaded RLD-USB-series 709 is specifically designed foruniversalserial bus (USB) applications with lower resistance, faster trip timesand lower voltage drop. 13
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  15. 15. Low Current Programmed Poly Fuse- High energy is forcing the - Relatively high ohmic Tungsten seperation resistor- Break before Tungsten completely - Lifetime drift to lower removed resistor values possible Tungsten Plug Field Oxide Tungsten Plug Tungsten HALOTungsten Silicide Tungsten SilicidePoly Silicon Poly Silicon Tungsten Field Oxide Substrate Substrate
  16. 16. THANKING EVERYONE FOR YOUR KIND PERUSAL THIS PRESENTATION IS PREPARED BY: ASANSOL ENGINEERING COLLEGE ELECTRICAL DEPERTMENT 16

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