Function, working principle and parameters of fuse — SUNMATE

（1） Function of fuse

Prevent long-term overload operation of the load

（2） Operating principle of fuse

During normal operation, it only serves as a connection in the circuit; Based on its extremely small resistance, part of the electrical energy is converted into thermal energy to detect the current. As long as the current through the fuse is less than the rated value, the converted thermal energy can be emitted by radiation or conduction. When the current exceeds the rated value of the fuse, the thermal energy cannot be fully emitted. After a certain time of accumulation, the fuse will be blown to protect the subsequent circuit.

（3） Parameters

3.1 Rated current

Firstly, calculate the maximum current Imax when the circuit is running at full load, and then derate it by 75% for use;

3.2 I2t

The thermal energy that the fuse can resist instantly is related to the capacity of the subsequent bus capacitance; The bus capacitance is large, which can cause a long charging time for the capacitor when it is first powered on, resulting in a large I2t;

Assuming an input voltage of 264VAC (220V+10%), the maximum value is 373V. Assuming a bus capacitance of 120uF, through the following circuit simulation, the charging time is 1.5ms, and the peak current is 373V/(1.5+2.65)=89.87A

Replacing the capacitor with 1000uF yields a charging time of 3.5ms and a constant peak current of 89.87A

3.3 Rated voltage

It refers to the maximum voltage that the fuse can withstand at the moment of fusing; When the fuse works normally, the voltage at both ends is very low. After the fuse is blown, one end is L live wire, and the other end may appear to be N zero wire. If the withstand voltage is not enough, it will cause air breakdown, causing danger; For AC input of 220VAC, the general rated voltage is 250VAC

3.4 Certification

The fuse is a key component and requires certification