How to correctly choose fuse (such as electronic [TERGY] tage brand now to illustrate the common fuse size 120608050603).
Chip fuse is mainly used in digital cameras, laptops, mobile phones and other electronic products.. From the traditional glass tube fuse, to a miniature fuse, fuse, because of the differences in product technology, their selection of the focus is slightly different.

The selection of the chip fuse relates to the following factors:
1, the normal operating current circuit. The working current of the fuse shall not exceed 75% of the rated current of the fuse.
2, pulse, impulse current, surge current, starting current and circuit transient value. 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 size of the circuit and the overload current is the shortest and the longest time. The use of oscilloscope test and theoretical calculation is usually required to determine the magnitude of the overload current. 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, the ambient temperature of the fuse. When applying for a portable device, a fuse is used to consider the temperature rise of the fuse, which is the reduction of the rated current of the fuse. The ambient temperature of the fuse should be within the specified operating temperature range, when the ambient temperature is above 25 degrees Celsius, the temperature reduction curve should be used as a reference.
6, applied voltage on the fuse. Commonly used in portable devices, the circuit operating voltage is not high, as long as the chip fuse rated voltage higher than the operating voltage of the circuit, you can rest assured that the use of.
7, product certification. For example, exports to North America, there must be a UL or CSA certification. Currently exported to Europe‘s products also need to comply with the EU‘s RoHS directive, which is commonly referred to as the SGS and other environmental certification. Here are some of the common parameters and terminology used in fuse selection. Normal operating current: operating at 25 C, the current rating of the fuse is typically reduced by 25% in order to avoid harmful fuse links. Most conventional fuses have a lower melting temperature for the materials used. Therefore, the fuse is sensitive to changes in ambient temperature. For example, at ambient temperature of 25 degrees Celsius, a fuse with a current rating of 1A is typically not normally working in a circuit with a steady-state current greater than 0.75A.
Voltage rating: the voltage rating of the fuse must be equal to or greater than the effective voltage of the circuit. The standard voltage rating series of general patch fuses are 24V, 32V, 48V, 63V, 125V.
Resistance: the resistance of the fuse is not very important in the whole circuit. But for a fuse with a number of less than 1, the resistance will have a zero point, so the problem should be considered when using a fuse in a low voltage circuit. Most of the fuse is made of a material with a positive temperature coefficient, so it is also divided between the cold resistance and the thermal resistance.
Ambient temperature: fuse is a temperature sensitive element. The current carrying capacity of the fuse, the experiment is carried out under the condition of 25. The higher the temperature of the environment, the higher the working temperature of the fuse, the current carrying capacity of the fuse is lower, the shorter the life is. On the contrary, it will extend the life of the fuse at relatively low temperatures.
Fuse Rated Capacity: also known as breaking capacity. Fuse rated capacity is the maximum allowable current that fuses can fuse at rated voltage. When a short circuit, the fuse will be through a large number of normal operating current large transient current overload. Safe operation requires the fuse to remain in full state (no burst or break).
Thermal energy: refers to the energy required to fuse the fuse links, using I2t, read as "ampere square seconds".
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 fuse time is less than 0.008 seconds. The purpose of this test is to ensure that the heat generated is not enough time to run away from the fuse component through the heat conduction, that is, all the heat energy used to fuse the fuse.

Thus, the fuse, taking into consideration the normal working current, fault current, I2t value, temperature, resistance and ratings reduction.


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