Polyfuses is a new standard for circuit protection. It is re-settable by itself. Many manufactures also call it as Polyswitch or Multifuse. Polyfuses are not fuses but Polymeric Positive temperature Coefficient Thermistors (PPTC). We can use several circuit protection schemes in 'power supplies to provide protection against fault condition and the resultant and over temperature damage. Current can be accomplished by using resistors, fuses, switches, circuit breakers or positive temperature coefficient devices.Resistors are rarely an acceptable solution because the high power resistors required are expensive. One shot fuses can be used but they might fatigue and they must be replaced after a fault event. Another good solution available is the resettable Ceramic Positive Temperature Coefficient (CPTC) device. This technology is not widely used because of its high resistance and power dissipation characteristics, These devices are also relatively large and" vulnerable to cracking as result of shock and vibration,The preferred solution is the PPTC device, which has a very. Low resistance in normal operation and high resistance when exposed to fault. Electrical shorts and electrically overload circuits can cause over current and over temperature damage.Like traditional fuses: PPTC devices limit the flow' of dangerously high current during fault condition. Unlike traditional fuses, PPTC devices reset after the fault is cleared and the power to the circuit is removed. Because a PPTC device does not usually have to be replaced after it trips and because it is small enough to be mounted directly into a motor or on (I circuit board, it can be located inside electronic modules, junction boxes and power distribution centers.