Fuse Resistors serve a dual purpose, a resistor and a fuse. They are designed so that they will open with a large surge current. The fusing current is calculated based on the amount of energy required to melt the resistive material (the melt temperature plus the amount of energy required to vaporize the resistive material). These resistors will normally run hotter than a normal precision or power resistor so that a momentary surge will bring the resistive element up to fusing temperature. Some designs create a hot spot inside the resistor to assist in this fusing. Calculations are made and samples are produced to verify the calculations. The major unknown is the heat transfer of the materials, which can be quite significant for pulse of long duration, and is very difficult to calculate. Mounting of these devices is critical because it will effect the fusing current. These are quite often made to mount in fuse clips for more accurate fusing characteristics.
No comments:
Post a Comment