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Working principle of the resettable fuse
DATE:2020-12-13 15:21Reading volume:544

             Ordinary fusing fuse will blow when the voltage is too high, and it needs to be replaced before it can work normally. The majority of businesses can love the SMD resettable fuse because it can be reused, not a one-time fuse.

PPTC is a polymer thermistor with a positive temperature coefficient, which is used for over-current protection and can replace the current fuse. When the circuit works normally, its resistance value is minimal (the voltage drop is tiny). When the circuit temperature rises due to over-current, the resistance value increases sharply by several magnitude orders. The current circuit is reduced to below the safe value so that the following circuit is protected. After the over-current disappears, it automatically returns to the low resistance value. Its effect is similar to that of the switch element, but its response speed is slow.

The operation principle of the resettable fuse is a kind of dynamic balance of energy. The current flowing through the resettable fuse generates heat due to the relationship between the fuse. The generated heat is totally or partially distributed to the environment, and the heat not emitted will increase the temperature of the element. In normal operation, the temperature is relatively low, and the heat generated is in balance with the heat emitted. When the current flowing through the fuse increases or the ambient temperature rises, the resettable fuse still does not act if the balance between the generated heat and the heat emitted is reached. When the current or ambient temperature increases again, the resettable fuse will reach a higher temperature. If the current or ambient temperature continues to increase at this time, the heat generated will be greater than the heat emitted, making the temperature of the resettable fuse increase sharply. At this stage, a small temperature change will cause a substantial increase in the resistance value. At this time, the resettable fuse is in the high resistance protection state with impedance. As long as the heat generated by the applied voltage is enough to recover the heat emitted by the resettable fuse, the components can always be in the action state (high resistance) under the changing state. When the applied voltage disappears, the resettable fuse will automatically recover.