The main difference between fast-blow fuse and slow-blow fuse is its ability to withstand instantaneous pulse current. Technically speaking, slow-blow fuse has a larger melting heat value, and the energy required to blow the fuse is larger. For fuses of the same rated current In other words, slow fusing is much stronger than fast fusing. Because the slow-blow fuse is larger than the fast-blow fuse of the same specification, when an overcurrent occurs in the circuit, the fusing time will be slower than the fast-blow fuse.
Fast-acting and slow-acting fuses are often used in different circuits because of their differences. For example, pure resistive circuits (no or little surge) or circuits that need to protect sensitive devices such as ICs must use fast-acting fuses. It is best to use slow blow fuses for capacitive or inductive circuits (surges when switching on and off) and power input and output parts. In addition to protecting IC circuits, most occasions where fast-acting fuses are used can be switched to slow-acting fuses to improve their anti-interference ability. However, if the slow blow is used in the place where the fast blow is used, the fuse will be blown when the machine is turned on.
In practical applications, power modules often have inrush currents or rush currents. That is, the currents of some circuits are several times higher than usual at the moment of switching. Generally, the current peaks are very high and the occurrence time is short. A normal ordinary fuse cannot withstand this current. If it is used, it will cause the circuit to fail to start normally. Changing to a large-size current fuse will cause the circuit to fail to protect against overload current. Therefore, choosing a slow-blow fuse can solve this problem and avoid that the instantaneous current generated by the module at the start-up moment exceeds its limit value, and it will not fuse at the start-up moment, but continuously exceed the limit value.
It should be noted that if the fuse is too small, it will easily cause false fusing, and if it is too large, it will not protect it, and it will easily cause a circuit input short circuit and cause the power supply to be interrupted.