1. Maintenance function. Usually, the extra current of the fuse must be larger than the normal operating current of the circuit, and it has certain overload capability, but the margin cannot be too large.

2. Carrying function. That is the ability to withstand pulses. When a fuse is used, there are more chances of normal current fluctuations or instantaneous pulses than fault overcurrent. This consideration is particularly important for the application of the fuse.

3. Safety function. A high-quality and reliable fuse must ensure safety before, during and after its operation, that is, it is safely turned on and blown. Appropriate fusing characteristics and additional current; satisfactory and reasonable melting heat value; and appropriate breaking ability, additional voltage and safety certification are necessary conditions to ensure the main functions of the fuse. The following factors will affect the performance of the fuse:

1. The internal resistance of the fuse: the increase of the internal resistance at the beginning or the increase of the internal resistance after the fuse is aging will change the heat dissipation conditions of the fuse, so as to make the melting time of the fuse faster;

2. Connection of the fuse: The reliable connection of the fuse in the circuit is an important part of ensuring the performance of the fuse. If the touch resistance of the connection part increases, the consequences will be the same as the increase of the internal resistance;

3. Surrounding heat dissipation conditions: the distance between the fuse and the heating element, the density of the components in the circuit, the cross-sectional area and the length of the connecting wire or the PC board are all related;

For small-size fuses, if their own internal resistance is relatively large and the operating voltage is very low, sometimes there will be no current output. This is not a problem with the fuse, but caused by other external factors. In addition, if the fuse technical parameters, fusing characteristics, extra current, extra voltage, breaking capacity, etc. are inappropriate, it will definitely affect the normal performance of the fuse.