With the development of the electronics industry, especially the microelectronics industry, miniature fast fuses for circuit protection have been more and more widely used. Miniature fuses have also been developed into a variety of shapes, different specifications to adapt to the requirements of different equipment. At present, miniature fuse is used in instrumentation, industrial control, mapping facilities, small motors and other industrial equipment; applied to residential power supply systems, switches, household appliances, audio-visual equipment and so on in people’s daily lives; widely used in notebook computers, desktop computers and their various accessories, network facilities and other micro devices. In short, miniature fuse can be said to be almost everywhere in our lives, that if we need to install their own miniature fuse should be how to choose?

Miniature fuse working principle.

To pick a good miniature fuse we must first understand its working principle. Current through the wire will have a part of the energy into heat, when the miniature fuse normal operation, the heat generated will be through the shell and the environment for heat exchange, to achieve a balance. When there is a problem with the circuit, the current will suddenly increase, resulting in a large amount of heat will destroy the original balance, resulting in a large amount of heat gathered on the wire to make the wire gasification or liquefaction. The circuit is thus interrupted to protect the circuit and prevent the excessive current from damaging the equipment in the circuit or even causing a fire.

Selection of miniature fuses must be considered several issues

On the basis of understanding the parameters of the circuit used, select a fuse according to the items of normal current, fusing current (current and time to be fused), open circuit voltage, short circuit current, inrush current), current not cut, time and number of times), and ambient temperature).

1.Normal current: First, we must know the normal current flowing through the fuse in the circuit used. Usually we pre-set a derating amount and then select according to the following principle:The normal current must be less than the product of the rated current and the derating factor.

2.Breaking Current: According to UL code, fuses should blow quickly at twice the rated current. However, in most cases, to ensure reliable melting, we recommend that the melting current should be greater than 2.5 times the rated current. Also, if the fusing time is important, be sure to refer to the fusing characteristics chart provided by the manufacturer to determine this.

3.Open circuit voltage: Generally, the open circuit voltage should be selected to be less than the rated voltage. For example, when using a fuse with a rated voltage of DC24V in an AC100V circuit, the fuse may ignite or break.

4.Short-circuit current: The maximum value of current flowing in case of a short-circuit in a circuit is called short-circuit current. For each fuse, the rated breaking capacity is specified, and the fuse must be selected to prevent the short-circuit current from exceeding the rated breaking capacity. If a fuse with a small breaking capacity is selected, the fuse may rupture or cause a fire.

5.Inrush current: Observe the pulse current waveform (impulse current waveform) and calculate its energy using the I2t value (Joule integral value). Inrush currents of different sizes and durations have different effects on fuses. The ratio of the I2t value of the inrush current to the I2t value of a single pulse determines the number of times the fuse can withstand the inrush current.

Other issues requiring attention

In actual use, miniature fuses in the installation conditions, chemical resistance, resistance to ultrasonic cleaning and other aspects of special requirements and problems, must be confirmed by the manufacturer in advance.

Micro fuses are different from common electronic components such as chip resistors and chip capacitors. Their specifications vary greatly due to differences in manufacturers. In addition, the actual installation will have some impact on the heat dissipation of the printed board and wiring. Therefore, the selection of miniature fuses should ultimately be determined by the status of the product.