SMD fuse how to choose?
1 SMD fuses mainly used in lithium batteries, digital camera, inverter, LED drive, notebook, backlight, LCD driver circuit, electric tools, electric toys and other electronic products. The fuse from the traditional glass tube, micro fuse, fuse, due to differences in product process, their selection of the focus is slightly different.
2 fuse selection involves the following factors: ED driver, notebook, backlight, LCD driver circuit, electric tools, electric toys and other electronic products. The fuse from the traditional glass tube, micro fuse, fuse, due to differences in product process, selection of their focus is slightly different, the impact of pulse. Current, inrush current, starting current and transient circuit. Fuse is particularly concerned about this, because the process of small size brings, the impact resistance of the fuse was far less than that of the rated current of the fuse in a glass tube fuse or other large volume.
3 the current of the circuit and the shortest and longest time of overload current. Usually need to use oscilloscope to test and theoretical calculation combined determine the overload current size. The basic requirements of the fuse is not the off time can not be broken (such as when the surge current), the off time must be in the appropriate time off (such as when the overload current need to cut off).
4 resistance. The resistance fuse has certain effects on some circuit: if the resistance is too large to install fuse in some circuits, it will affect the system parameters of the circuit, the circuit is not working properly.
5 fuse ambient temperature. The use of chip fuses for portable devices should be appropriate to consider the temperature rise of the fuse. The ambient temperature of the fuse shall be within the specified operating temperature range, and when the ambient temperature around the fuse is more than 25 DEG C, the temperature reduction curve should be used for degradation.
6 applied voltage on the fuse. SMD fuses are commonly used in portable devices, circuit operating voltage is generally not high, as long as the SMD fuse rated voltage higher than the circuit operating voltage, you can rest assured that the use of.
7 product certification. For example, exported to North America, there must be a UL or CSA certification. Currently exported to Europe products also need to comply with the EU‘s RoHS directive, which is commonly referred to as SGS and other environmental certification. If you have any other questions, you can contact Sutter to get the solution. Here are some of the common parameters and terminology in the selection of the fuse.
Normal operating current: operating at 25 C, the current rating of the fuse should be reduced by 25% to avoid harmful fuses. Most conventional fuses have low melting temperatures. Therefore, the fuse is more sensitive to changes in ambient temperature. For example, at a temperature of 25 DEG C, a fuse with a current rating of 1A is normally not able to work in a circuit with a steady-state current greater than 0.75A.
Voltage rating: fuse voltage rating must be equal to or greater than the effective circuit voltage. General SMD fuse standard voltage rating series 24V, 32V, 48V, 63V, 125V.
Resistance: the resistance of the fuse is not very important in the whole circuit. However, the resistance of the fuse with less than 1 amperes will have a few ohms, so the problem should be considered when using the fuse in the low voltage circuit. Most of the fuses are made of positive temperature coefficient materials, so there is also a difference between cold resistance and thermal resistance.
Ambient temperature: fuse is temperature sensitive element. The current carrying capacity of the fuse is carried out at a temperature of 25 DEG C. The higher the ambient temperature, the higher the operating temperature of the fuse, the lower the current carrying capacity of the fuse, the shorter the life. On the contrary, it will prolong the life of fuse at relatively low temperature.
Rated capacity of fuse: also known as breaking capacity. The rated capacity of the fuse is the maximum permissible current for the fuse to be able to fuse at rated voltage. When the short circuit, the fuse will pass through the overload current than the normal operating current. Safe operation requires the fuse to remain intact (no burst or break).
Nominal heat of fusion: refers to the energy required to fuse the fuse components, with I2t, read as "ampere second". In general, certification authority, to test: melting heat energy by applying a current increment and the measurement of melting occurred time to fuse, if the melting does not occur in about 0.008 seconds or longer, then increase the intensity of pulse current. Repeat the experiment until the fusing time is within 0.008 seconds. The purpose of this test is to ensure that the heat generated does not have enough time to run away from the heat transfer of the fuse component, that is to say, all the heat energy is used to fuse the fuse.
Therefore, the fuse, taking into consideration the normal working current, fault current, I2t value, temperature, resistance and ratings reduction.