Fuses protect electronic devices from electrical current and prevent serious damage caused by internal failures. Therefore, each fuse has a rating, and the fuse will blow when the current exceeds the rating. When a current is applied to a fuse that is between the conventional unfused current and the rated breaking capacity specified in the relevant standard, the fuse shall operate satisfactorily and without endangering the surrounding environment.
The expected fault current of the circuit where the fuse is installed must be less than the rated breaking capacity current specified in the standard. Otherwise, when the fault occurs, the fuse will continue to fly, ignite, burn the fuse, melt together with the contact, and the fuse mark cannot be recognized. Of course, the breaking capacity of the inferior fuse can not meet the requirements stipulated in the standard, and the use of the same harm will occur.
In addition to fusing resistors, there are also general fuses, thermal fuses and self-restoring fuses. The protective element is generally connected in series in the circuit, it in the circuit of over current, over voltage or overheating and other abnormal phenomenon, will immediately fuse and play a protective role, can prevent further expansion of the fault.
(1) Ordinary Fuses
Ordinary fuses, commonly known as fuses or fuses, belong to fuses that cannot be recovered, and can only be replaced with new fuses after fuses. It is indicated by “F” or “FU” in the circuit.
Structural Characteristics of Common Fuses
Common fuses usually consist of glass tubes, metal caps, and fuses. The two metal caps are placed at both ends of the glass tube. The fuse (made of low-melting metal material) is installed in the glass tube. The two ends are welded to the center holes of the two metal caps respectively. When in use, the fuse is loaded into the safety seat and can be connected in series with the circuit.
Most fuses of fuses are linear, only color TV, computer monitors used in delay fuses for spiral fuses.
Main Parameters of Common Fuses
The main parameters of ordinary fuse are rated current, rated voltage, ambient temperature and reaction speed. Rated current, also known as breaking capacity, refers to the current value that the fuse can break at rated voltage. The normal operating current of the fuse should be 30% lower than the rated current. The current rating of domestic fuses is usually marked directly on the metal cap, while the color ring of imported fuses is marked on the glass tube.
Rated voltage refers to the most regulated voltage of the fuse, which is 32V, 125V, 250V and 600V four specifications. The actual working voltage of the fuse should be lower than or equal to the rated voltage value. If the operating voltage of the fuse exceeds the rated voltage, it will be quickly blown out.
The current carrying capacity of the fuse is tested at 25℃. The service life of fuses is inversely proportional to the ambient temperature. The higher the ambient temperature, the higher the operating temperature of the fuse, the shorter its life.
Response speed refers to the speed with which the fuse responds to various electrical loads. According to the reaction speed and performance, fuses can be divided into normal response type, delay break type, fast action type and current limiting type.
(2) Thermal Fuses
Thermal fuse, also known as temperature fuse, is a kind of unrecoverable overheating insurance element, widely used in all kinds of electric cookware, motor, washing machine, electric fan, power transformer and other electronic products. Thermal fuses can be divided into low melting point alloy type thermal fuses, organic compound type thermal fuses and plastic-metal type thermal fuses according to the different temperature sensing body materials.
Low Melting Point Alloy Type Thermal Fuse
The temperature sensing body of low melting point alloy type hot fuse is machined from alloy material with fixed melting point. When the temperature reaches the melting point of the alloy, the temperature sensing body will be automatically fused, and the protected circuit will be disconnected. According to its different structure, low melting point alloy type hot low melting point alloy type hot fuse can be divided into gravity type, surface tension type and spring reaction type three.
Organic Compound Type Thermal Fuse
Organic compound thermal fuse is composed of temperature sensing body, movable electrode, spring and so on. Temperature sensing body is processed from organic compounds with high purity and low fusing temperature range. Normally, the movable electrode and the fixed end point contact, the circuit is connected by the fuse; When the temperature reaches the melting point, the temperature sensing body automatically fuses, and the movable electrode is disconnected from the fixed end point under the action of the spring, and the circuit is disconnected for protection.
Plastic – Metal Thermal Fuse
Plastic-metal thermal fuses adopt surface tension structure, and the resistance value of temperature sensing body is almost 0. When the working temperature reaches the set temperature, the resistance value of the temperature sensing body will suddenly increase, preventing the current from passing through.
(3) Self-Restoring Fuse
Self-restoring fuse is a new type of safety element with overcurrent and overheat protection function, which can be used repeatedly.
Structural Principle of Self – Restoring Fuses
Self-restoring fuse is a positive temperature coefficient PTC thermosensitive element, made of polymer and conductive materials, etc., it is in series in the circuit, can replace the traditional fuse.
When the circuit is working normally, the self – restoring fuse is on. When there is an overcurrent fault in the circuit, the temperature of the fuse itself will rise rapidly, and the polymeric material will quickly enter the high resistance state after being heated, and the conductor will become an insulator, cutting off the current in the circuit and making the circuit enter the protection state. When the fault disappears and the self-restoring fuse cools down, it takes on a low resistance conduction state and automatically connects the circuit.
The operating speed of the self-restoring fuse is related to the abnormal current and the ambient temperature. The larger the current is and the higher the temperature is, the faster the operating speed will be.
Common Self – Restoring Fuse
Self – restoring fuses have plug-in type, surface mounted type, chip type and other structural shapes. The commonly used plug-in fuses are RGE series, RXE series, RUE series, RUSR series, etc., which are used in computers and general electrical appliances.
Post time: Apr-20-2023