The most common part of the circuit over-current protection element is small tubular fuse, which is composed of two main parts, namely, the tube body with metal connection terminal at both ends and the metal melt in the tube. The shell part of the fuse is used to support and connect. Most of the fuses are cylindrical, which is called tubular; The key function is determined by the internal melt.
Fuse is series in the circuit, generally requires its resistance to be small (power consumption is small), so when the circuit is normal, fuse is only equivalent to a conductor, can be used stably for a long time; When current fluctuation occurs due to power supply or external interference, fuse can also bear a certain range of overload; Only when there is a large overload current - fault or short circuit - in the circuit, the fuse will act, and the circuit safety can be protected by breaking the current.
When the fuse is energized, the temperature of the melt will rise due to the heat converted by current. When the normal working current or the allowable overload current is loaded, the heat generated by the current and the heat emitted by the melt, shell and surrounding environment, convection and conduction can be gradually balanced; If the heat dissipation speed cannot keep up with the heating, these heat will be accumulated on the melt one by one, so that the melt temperature rises. Once the temperature reaches and exceeds the melting point of the melt material, it will melt, thus breaking the current and playing a role of safety protection.
Rated current: nominal working current of fuse, code: in
Rated voltage: nominal working voltage of fuse, code: UN
Voltage drop: voltage drop at both ends of fuse at rated current, code: UD
Cold resistance: resistance value of fuse when it is not working, code: RN
Overload capacity: overload current that fuse can work for a long time (some varieties can be in high temperature conditions)
Fuse characteristic: the performance index of fuse operation -- the function relation between load current and fuse time, that is, time / current characteristic (also known as an an-s characteristic).
There are usually two ways of expression:
Fuse characteristic curve: the curve is made up of the average fuse fuse fuse time coordinate point under different current load, taking load current as X coordinate, fuse time as y coordinate. Each fuse of model and specification has a corresponding curve to represent its fusing characteristics, which can be used for reference when selecting fuse.
Fuse characteristic table: a table composed of several representative load current values and corresponding fusing time. Each type of fuse has a fuse characteristic table which can be used to test the fuse.
Breaking capacity: the most important safety index of fuse - the maximum current value that fuse can break safely when the overload current (short circuit) is large. Safety breaking refers to the phenomenon that the fuse breaking circuit does not cause splashing, burning, explosion and other hazards to the safety of the surrounding components and even the human body. Code: IR
Melting heat value: the nominal energy value required to melt the fuse melt, which is a fuse