With the miniaturization and placement of electronic components, fuses are also moving towards small placement, and the application of chip fuses is becoming more and more extensive. They are used in computer and peripheral interfaces, flat-panel TVs, mobile phones, and automotive electronic circuits. And the overcurrent protection of battery packs, etc. have already shown their skills. In addition to the common fuse type fuses, in recent years, the rise of PPTC resettable fuses (polymer positive temperature coefficient thermistors) has brought a new dimension to the protection of IT equipment.

Like SMD diodes, SMD ICs and other components, SMD fuse currently has no unified calibration method, so the codes used by each manufacturer are different. Sometimes, the same code (in different series) of the same manufacturer represents different rated currents. There are also some weird codes that even find it difficult to identify them, which adds a lot of trouble to maintenance replacement.

1. Identification of commonly used fusing type chip fuses

The fusible chip fuse (chip fuse) has basically the same function as the commonly used fuse. It can work normally under the rated current (when the circuit is normal). When the circuit fails to reach or exceed the fusing current value, it will blow. Avoid further expansion of the fault, thereby protecting the circuit. Fuse (fuse) is divided according to the melting speed: super slow fuse (usually represented by TT), slow fuse (usually represented by T), medium-speed fuse (usually represented by M), fast fuse (one ship is represented by F) ) And very fast fuses (usually represented by FF) and other five types. According to the maximum breaking current, it can be divided into low breaking type (L) and high breaking type (H). The marking method of fusing type chip fuses can generally be divided into two types: direct marking method and code marking method, and code marking method can be subdivided into letter (or number) marking method and graphic marking method.

1. Direct labeling

SMD fuses mark the main characteristic parameters directly on the front of the component, which is called direct labeling method, or direct labeling method for short. The direct labeling method is generally used for the slightly larger "square-head" porcelain tube insurance and rectangular parallelepiped plastic-encapsulated patch insurance.

2. Code notation

Code notation is generally applicable to small-volume SMD components. Due to the limitation of the surface area of the component, it is inconvenient to use the direct marking method. Only one or a few simple symbols (letters, numbers or geometric figures) can be printed on the front of the component. The code marking method is divided into letter (or number) marking method and Graphical notation. As there is no unified code formulation rule, sometimes the same code may indicate different rated currents due to different manufacturers. This undoubtedly increases the difficulty of the solution. As for the rated voltage and other parameters and characteristics, they cannot be directly obtained from the code. If it is a new product purchased, the supplier may be required to provide parameters or related information. If it is the fuse on the board to be repaired, the rated voltage can be roughly estimated based on the actual working voltage of the part of the circuit. Another method is to judge its manufacturer and its product series based on its shape, size, color, and code type and arrangement, so as to find detailed product information. However, the last method requires a better understanding of the manufacturers and product series of patch insurance. Beginners must practice repeatedly and accumulate summaries before they can master it.