Definition of Fuse & Circuit Breaker:
When the circuit breaks down or is abnormal, the current increases continuously, and the increased current may damage some important devices in the circuit, burn the circuit or even cause fire. If the fuse is correctly placed in the circuit, the fuse will fuse and cut off the current when the current abnormally rises to a certain height and heat, so as to protect the safe operation of the circuit.
Fuse introduction
Fuse shape:
1. Filamentous. Early primitive fuses were directly locked with screws and were used for old switches and sockets of various sizes.
2. Sheet (bare sheet). It is more convenient to use than the old silk.
3. Glass tube. There are several different sizes, which are common in electronic products.6.3 x 32 mm (diameter x length)5 x 20 mm
4. Ceramic tube. There are several different shapes and sizes to avoid glass bursting.
5. Plastic sheet with metal sheet pin: Automobile fuse.
6. Surface bonding element (SMD) type.
7. Cylindrical, plug-in type: directly welded to the circuit board, used inside the product.
Marking of fuse
Mark most fuses are marked on the body or end cap with marks to indicate their rating. However, the "chip type" fuse has little or no marking, which makes it very difficult to identify.
Fuses may have similar and significantly different characteristics, and their marking is determined. Fuse marking usually conveys the following information: ampere fuse rated voltage rating fuse time current characteristics, i.e. speed fuse approved by national and international standards bodies manufacturer / product number / series interruption capability
Function of fuse
The fuse invented by Edison more than 100 years ago is used to protect the expensive incandescent lamp at that time. With the development of the times, the fuse protects the electronic / power equipment from current / overheating injury and avoids serious injury caused by internal failure of electronic equipment.
Working principle of fuse
When the current flows through the conductor, the conductor will heat up because there is a certain resistance in the conductor. And the calorific value follows this formula: q = i2rt. Where q is the calorific value, 0.24 is a constant, I is the current flowing through the conductor, R is the resistance of the conductor, and t is the time when the current flows through the conductor; According to this formula, it is not difficult for us to see the simple working principle of the fuse. When the material and shape of the fuse are determined, its resistance R is relatively determined (if its resistance temperature coefficient is not considered). When the current flows through it, it will generate heat, and its calorific value is increasing with the increase of time. The current and resistance determine the speed of heat generation, and the structure and installation of the fuse determine the speed of heat dissipation. If the speed of heat generation is less than the speed of heat dissipation, the fuse will not blow. If the rate of heat generation is equal to the rate of heat dissipation, it will not fuse for a long time. If the rate of heat generation is greater than the rate of heat dissipation, more and more heat will be generated. Because it has a certain specific heat and mass, the increase of heat is reflected in the increase of temperature. When the temperature rises above the melting point of the fuse, the fuse will blow. This is how the fuse works. We should know from this principle that when designing and manufacturing fuses, you must carefully study the physical properties of your selected materials and ensure that they have consistent geometric dimensions. Because these factors play a vital role in the normal operation of the fuse. Similarly, when you use it, you must install it correctly.
Classification of fuses
According to the protection form, it can be divided into overcurrent protection and overheating protection. The fuse used for overcurrent protection is commonly known as the fuse (also known as current limiting fuse). The fuse used for overheating protection is generally referred to as "temperature fuse". Temperature fuse is divided into low melting point alloy shape, temperature sensing trigger shape, memory alloy shape and so on (the temperature fuse is used to prevent the temperature of heating appliances or easily heating appliances from being too high, such as hair dryer, electric iron, electric rice cooker, electric furnace, transformer, motor, etc.; it responds to the temperature rise of electric appliances and does not care about the working current of the circuit. Its working principle is different from the "current limiting fuse").
According to the scope of use, it can be divided into: power fuse, machine tool fuse, electrical instrument fuse (electronic fuse) and automobile fuse. Thermal Fuse
According to the volume integral, it can be divided into: large, medium, small and micro.
According to the rated voltage, it can be divided into: high voltage fuse, low voltage fuse and safety voltage fuse.
According to breaking capacity, it can be divided into high breaking capacity fuse and low breaking capacity fuse.
According to the shape, it can be divided into: flat head tubular fuse (which can also be divided into internal welding fuse and external welding fuse), pointed tubular fuse, guillotine fuse, spiral fuse, plug-in fuse, flat fuse, wrapped fuse and patch fuse.
According to the fusing speed, it can be divided into: extra slow fuse (generally represented by TT), slow fuse (generally represented by T), medium speed fuse (generally represented by M), fast fuse (generally represented by F) and extra fast fuse (generally represented by FF).
According to the standard, it can be divided into: European fuse, American fuse and Japanese fuse.
According to the type, it can be divided into: current fuse (patch fuse, micro fuse, plug-in fuse and tubular fuse), temperature fuse (RH [block type], RP [resistance type], ry [metal shell]) and self recovery fuse (plug-in, lamination and patch).
It can be divided into: patch type 0603080512061210181220162920; Non patch type Φ two point four × 7， Φ three × 7， Φ three point six × 10， Φ four point five × 15， Φ five × 20， Φ five point one six × 20， Φ six × 25， Φ six × 30， Φ six × 32， Φ eight point five × 8， Φ eight point five × eight × 4， Φ ten × 38， Φ fourteen × 51。
Resettable fuse
Low zero power resistance: the self resetting fuse has low impedance, small power loss and low surface temperature during normal operation.
Fast over-current protection speed: due to its own material characteristics, the response speed of over-current state of self resetting fuse is much faster than that of other over-current protection devices.
Self locking operation: the self resetting fuse is in the overcurrent protection state and locked in the high resistance state with very small current. The low resistance state will be restored only after the power supply is cut off or the overcurrent disappears.
Automatic reset: after the self resetting fuse plays the role of overcurrent protection (troubleshooting), it will reset automatically without disassembly and replacement. High current resistance: the self resetting fuse has excellent high current resistance, and some specifications can withstand 100A current impact.
Application: PPTC has a wide range of applications and can be used in various electronic products, communication products, power supplies, etc.
