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Do power module fuses choose slow-break or fast-break?

Pulished on Dec. 14, 2019

A fast-acting fuse will blow as long as the current exceeds its rated value, and can only be used for short-circuit protection, while the slow-blow fuse will remain intact when a non-fault pulse current occurs in the circuit, protecting the long-term current overload, and has short-circuit and overload protection functions.

The main difference between a fast-blow fuse and a slow-blow fuse is its ability to withstand instantaneous pulse current. Technically, slow-blow has a large melting thermal energy value, and the energy required for a outdoor fused cutouts to blow is relatively large. For fuses with the same rated current, In terms of slow blow, the ability to withstand pulses is much stronger than fast blow. Because slow-blow fuses are larger than fast-blow fuses of the same specification, when an overcurrent occurs in the circuit, the fuse time will be slower than the fast-blow fuse.

Because of their differences, fast-blow and slow-blow fuses are often used in different circuits, such as: purely resistive circuits (no or few surges) or circuits that need to protect sensitive components such as ICs. Fast-blow fuses must be used, and Capacitive or inductive circuits (surges when switching on and off), power input and output parts are best to use slow blow fuses. In addition to protecting the IC's circuit, in most cases where fast-blow fuses are used, slow-blow fuses can be used instead to improve their anti-interference ability. However, if you use a slow-blow in a place with a slow-blow, it will cause the fuse to break when you turn it on.

Fuse Cutout

Fuse Cutout

In practical applications, power modules often have inrush current or inrush current, that is, the instantaneous current of some circuits will be several times higher than usual at the time of switching. Generally, the current peak is high and the appearance time is short. The normal ordinary fuse cutout switch cannot bear this kind of current. If it is used, it will cause the circuit to fail to start normally. Replacement with a large-size current fuse will cause the circuit to fail to provide protection when overload current occurs. Therefore, choosing a slow-blow fuse can solve this problem and avoid the module's instantaneous current generated at the instant of startup exceeding its limit value. The module does not blow at the instant of startup, but continuously blows beyond the limit value.

It should be noted that if the fuse is too small, it will easily cause mis-fuse. If it is too large, it will not be protected, and it will easily cause a circuit input short circuit and cause power supply interruption.

How fuses distinguish between fast break and slow break

Some friends may pay more attention to the fast and slow disconnection of fuses, so how to distinguish between fast and slow disconnection of fuses has clearly become the focus of everyone's attention. The overhead line fittings supplier lead us to analyze how to distinguish fast interrupts from slow disconnections and explain the knowledge of certain fuses in the circuit.

Fuse generally has its special characteristics, such as different letters according to the fuse speed, slow fuse (T), middle fuse (M), fast fuse (F); according to international standards are divided into VDE (European regulations), UL (American Standard), PSE (Japanese Standard), etc.

In real life, we often encounter inrush or pulse currents. This means that the instantaneous current of some circuits will be several times higher than usual. Although its current peak is very high, but its appearance time is short, but ordinary fuses cannot withstand this current. If ordinary fuses are used, the circuit will not start normally. If the circuit is overloaded and cannot protect it, this slow fuse Solved this problem very well.