A micro fuse is a radial leaded subminiature fuse offered in either a cylindrical or rectangular form factor. Micro fuses were originally designed for the U.S. Space Program. The micro fuse is made with either glass, plastic or metal bodies. They are designed to be electrically equivalent to miniature glass cartridge fuses in a smaller package with higher tolerance to impact and vibration. Micro fuses can plug in to a PC board mounted fuse holder. Micro fuse voltage ratings typically range from 65 volts AC to 300 volts AC. Micro fuses with voltage ratings up to 450 volts DC are also available. Micro fuses are offered in fast acting or time lag versions.

Shape and structure editing and broadcasting

The shape of micro fuse can be divided into lead type and sheet type. If it is divided according to the structure of fuse element, it can be divided into linear and film type.

Select method to edit broadcast

In practical applications, it is not enough to select fuses only according to UL specifications.

1. Several problems that must be considered in selection

On the basis of understanding the parameters of the circuit used, the fuse is selected according to the following aspects: normal current, fusing current (current and time to fuse), open circuit voltage, short-circuit current, impulse current (current, time and times not cut off), and ambient temperature.

① Normal current: first of all, we must know the normal current flowing through the fuse in the circuit used. Usually, we need to set a derating amount in advance, and then choose according to the following principle: that is, the normal current must be less than the product of rated current and derating coefficient.

② Fusing current: according to UL specification, the fuse shall fuse quickly at twice the rated current. However, in most cases, in order to ensure reliable fusing, we recommend that the fusing current should be greater than 2.5 times the rated current. In addition, if the fusing time is important, it must also refer to the fusing characteristic diagram provided by the manufacturer for judgment.

③ Open circuit voltage: the open circuit voltage shall generally be selected to be less than the rated voltage. For example, when a fuse with a rated voltage of DC24V is used in an AC100V circuit, it may ignite the fuse or break the fuse.

④ Short circuit current: we call the maximum current flowing when the circuit is short circuited as short circuit current. For various fuses, the rated breaking capacity is specified. When selecting fuses, we must pay attention not to make the short-circuit current exceed the rated breaking capacity. If a fuse with small breaking capacity is selected, it may break the fuse or cause a fire.

⑤ Impulse current: observe the waveform of impulse current (pulse current waveform) and calculate its energy with i2t value (Joule integral value). The impact on the fuse is also different with the size and times of impulse current. The ratio of i2t value of impulse current to i2t value of single pulse fusing determines the times that the fuse can withstand impulse current.

2. Other issues needing attention

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

Micro fuse is different from ordinary electronic components such as chip resistor and chip capacitor. Due to the differences of manufacturers, its specifications are quite different. In addition, the actual installation will have a certain impact on the heat dissipation of printed board and wiring. Therefore, whether the selection of micro fuse is correct or not should be determined by the state of the product.