Principle of action of resettable fuse

　　The working principle of a resettable fuse is the dynamic balance of energy. The current flowing through the resettable fuse generates a certain degree of heat due to the thermal effect of the current (there is a resistance value in the resettable fuse). All or part of the heat generated is dissipated into the environment, but the remaining heat will increase the temperature of the resettable fuse element.

　　During normal operation, the temperature is low and the heat generated and dissipated reaches equilibrium. When the resettable fuse is in a low resistance state, it does not work. When the current flowing through it increases or the ambient temperature rises, if the generated and dissipated heat reaches equilibrium, the fuse will remain inactive.

　　If the current or temperature continues to rise at this time, the heat generated will be greater than the heat dissipation, causing a sharp increase in the temperature of the resettable fuse. Therefore, small temperature changes will lead to a significant increase in resistance, and the resettable fuse element will be in a high impedance protection state. The increase in impedance limits the current, and the current drops sharply in a short period of time, thereby protecting the circuit from damage. As long as the heat generated by the applied voltage is sufficient to meet the emitted heat, the resettable fuse in a changing state can always function (high resistance).

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