The selection method of miniature fuses

In practical applications, selecting fuses based solely on UL specifications is far from enough.
Several issues that must be considered when choosing
Based on understanding the parameters of the circuit used, select the fuse according to the following aspects: normal current, melting current (desired current and time to fuse), open circuit voltage, short circuit current, impulse current (current that has not been cut off, time and frequency), and ambient temperature.
① Normal current: Firstly, we must know the magnitude of the normal current flowing through the fuse in the circuit being used. Usually, we need to pre-set a reduction amount and then choose according to the following principle: the normal current must be less than the product of the rated current and the reduction coefficient.
② Fusing current: According to UL specifications, fuses should quickly fuse at twice the rated current. But in most cases, to ensure reliable melting, we recommend that the melting current should be greater than 2.5 times the rated current. If the circuit breaker time is important, it is also necessary to refer to the circuit breaker characteristic diagram provided by the manufacturer to make a judgment.
③ Open circuit voltage: The open circuit voltage should generally be selected as less than the rated voltage. For example, when using a fuse with a rated voltage of DC24V in an AC100V circuit, it may ignite the fuse or cause it to rupture.
④ Short circuit current: We refer to the maximum current that flows through a circuit during a short circuit as the short circuit current. For various fuses, the rated breaking capacity is specified, and we must be careful not to exceed the rated breaking capacity when selecting fuses. If a fuse with a small breaking capacity is selected, it may cause the fuse to rupture or trigger a fire.
⑤ Impulse current: Observe the waveform of the impulse current (pulse current waveform) and calculate its energy using the I2t value (Joule integral value). The impact on the fuse varies depending on the magnitude and frequency of the impulse current. The ratio of the I2t value of the impulse current to the I2t value of the single pulse fuse determines the number of times the fuse can withstand the impulse current.
2. Other issues that need to be noted
In practical use, any special requirements and issues regarding installation conditions, chemical resistance, ultrasonic cleaning resistance, and other aspects of miniature fuses must be confirmed in advance by the manufacturer.
Micro fuses are different from ordinary electronic components such as SMD resistors and capacitors. Due to differences in manufacturers, their specifications vary greatly. In addition, actual installation can have a certain impact on the heat dissipation of printed boards and wiring. Therefore, the selection of micro fuses should ultimately be determined by the condition of the product.