tube amp blown fuse symptoms.Working principle of self recovery fuse

　　The self recovery fuse is composed of specially treated polymer resin and conductive particles (CarbonBlack) distributed inside. Under normal operation, the polymer resin tightly binds conductive particles outside the crystalline structure, forming a chain like conductive electrical pathway. At this time, the self recovery fuse is in a low resistance state (a), and the heat generated by the current flowing through the self recovery fuse on the circuit is small and does not change the crystal structure. When a circuit experiences a short circuit or overload, the heat generated by the large current flowing through the self recovery fuse causes the polymer resin to melt, rapidly increase in volume, and form a high resistance state (b). The working current rapidly decreases, thereby limiting and protecting the circuit. After troubleshooting, the self recovery fuse cools and crystallizes again, shrinks in volume, and conductive particles form a conductive path again. The self recovery fuse returns to a low resistance state, thus completing the protection of the circuit without the need for manual replacement.

　　Modified epoxy resin was selected as the packaging material for polyethylene/carbon black self recovery fuses, and the influence of packaging on the thermal characteristics of the fuse was studied. The packaging layer affects the heat dissipation ability of the core material. When the current is large enough, the packaging has almost no effect on the action time of the fuse. When the current is small, the packaging layer cures at 120 ℃ (polyethylene melting point) due to the presence of a certain gap between the packaging layer and the core material, The heat dissipation ability of the core material decreases, and the thermal expansion of the core material can proceed smoothly, resulting in a shorter action time. Therefore, fuse encapsulation should be carried out at a temperature where the core material reaches maximum thermal expansion.

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