SMD fuses are mainly used in digital cameras, notebooks, mobile phones and other electronic products, from traditional glass tube fuses to small fuses and SMD fuses. Due to differences in product technology, the focus of their selection is slightly different. The selection of chip fuses involves the following factors:
1. Product certification. For example, export to North America, must have UL or CSA certification. Products currently exported to Europe also need to comply with the EU ’s RoHs directive, which is commonly referred to as SGS and other environmental certifications.
2. The normal working current of the circuit. The operating current through the fuse should not exceed 75% of the rated current of the fuse.
3. The applied voltage applied to the fuse. Generally, SMD fuses are used in portable equipment, and the circuit operating voltage is generally not high. As long as the rated voltage of the SMD fuse is higher than the circuit operating voltage, you can safely choose it.
4. The ambient temperature of the fuse. When SMD fuses are used in portable equipment, the temperature rise of the fuse should be properly considered, that is, the reduction of the fuse rated current. The ambient temperature when the fuse is working should be within the specified operating temperature range. When the ambient temperature around the fuse exceeds 25 ° C, the temperature reduction curve should be used to degrade it.
5. The magnitude of the overload current of the circuit and the shortest and the longest time that the overload current exists. It is usually necessary to use a combination of oscilloscope testing and theoretical calculation to determine the magnitude of overload current. The basic requirements for the fuse cannot be broken when it should not be broken (such as when an inrush current occurs), and it must be broken within an appropriate time. (For example, when there is an overload current that needs to be cut off).
6. Resistance. The resistance of the chip fuse has a certain effect on some circuits: if a fuse with an excessive internal resistance is installed in some circuits, it will affect the number of systems in the circuit, making the circuit not work properly.
7. Pulse, surge current, surge current, starting current and circuit transient value. SMD fuses pay particular attention to one point. Due to the process reasons brought by the small size, the impact resistance of SMD fuses is much smaller than that of glass tube fuses or other larger fuses with the same rated current.
The above are the application fields of SMD fuses and the precautions for selection.