SMD fuses are mainly used in digital cameras, notebooks, mobile phones and other electronic products, from traditional glass tube fuses to miniature fuses and SMD fuses. Due to differences in product technology, the focus of their selection is slightly different. The selection of chip fuses is also different
1. The normal operating current of the circuit. The operating current through the fuse should not exceed 75% of the rated current of the fuse.
2. Pulse, surge current, surge current, starting current and circuit transient value. SMD fuses pay particular attention to one point. Due to the technical 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.
3. The magnitude of the overload current of the circuit and the shortest and longest time for the overload current to exist. General requirements use oscilloscope testing and theoretical calculation to determine the magnitude of overload current. The basic requirements for the fuse can not be broken when the time should not be broken (for example, when the inrush current occurs), the broken time must be broken within the appropriate time (For example, the time when the overload current that needs to be blocked occurs).
4. Resistance. The resistance of the chip fuse has a certain effect on some circuits: if a fuse with an excessively large internal resistance is installed in some circuits, it will affect the number of circuits in the circuit, making the circuit unable to operate normally.
5. 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 operating 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.
6. 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, it can be selected with care.
Therefore, when selecting a chip fuse, it is necessary to consider the normal operating current, fault current, I2t value, ambient temperature, internal resistance and rated value reduction.