Complete Guide To Smd Chip Fuses: Types, Working Principle, And Selection Tips
What is a chip fuse?（Chip Fuse / SMD Fuse）
A chip fuse is a small-sized overcurrent protection component suitable for surface mount technology (SMT). Its main function is to cut off the circuit by melting once when there is an overcurrent or short circuit in the circuit, thereby protecting sensitive components from overheating, burning, and even causing fires and other dangers.
It is called a surface mount fuse because it adopts a flat and small package that can be directly soldered onto the surface of a PCB board. It can be mass-produced in conjunction with an automated surface mount machine. This packaging not only saves space but also reduces assembly costs, and is highly suitable for high-density electronic products such as smart phones, laptops, automotive electronic control units, wearable devices, network communication equipment, etc.
Compared with other types of fuses, glass tube fuses are larger in size and are mostly used in traditional electrical appliances and industrial equipment; self-resetting fuses can automatically reset, but they are relatively larger in size and have higher impedance; surface mount fuses melt completely at once, are smaller in size, have higher precision, and are suitable for modern electronic devices with limited space.
Classification of Chip Fuses
Classified by the melting speed
Fast Break Type: It can quickly cut off the circuit within milliseconds, effectively protecting sensitive components such as IC chips, MOS transistors, and diodes from overcurrent damage. It is commonly used in USB interfaces, precision instruments, and signal processing circuits. Slow-blow type: Allows a short period of surge current or startup current to pass through, and only melts when there is a continuous overcurrent. This type can prevent false actions caused by the instantaneous large current when equipment such as motors and lamps start up. It is commonly used in motor drives, lighting equipment, and power modules.
Classified according to rated parameters
The rated current ranges from several milliamperes to several amperes, such as 0.125A, 0.5A, 1A, 2A, 5A, etc. It needs to be selected according to the load requirements.
The common rated voltages include 32V, 63V, 125V, 250V, etc. They should be matched with the working voltage of the circuit and leave a safety margin.
Classified by packaging size
| Package Code | Dimensions (mm) |
|---|---|
| 0402 | 1.00 × 0.50 × 0.40 |
| 0603 | 1.60 × 0.81 × 0.48 |
| 1206 | 3.20 × 1.60 × 0.75 |
| 1214 | 3.20 × 3.60 × 1.10 |
Classify by characteristics
Ultra-fast type: It can respond quickly to even extremely short current shocks. High breaking capacity type: Suitable for applications with high current and high energy faults, ensuring that no arcing or fragments are produced during the fuse blowout.
The working principle of the chip fuse
The core of a chip fuse is a specially designed metal fuse, usually made of copper, silver or an alloy, and is encapsulated externally with ceramic or high-temperature resistant materials.
Under normal conditions, the current is lower than the rated value, the fuse temperature is low, it remains in the conducting state, and the resistance is very small, almost not affecting the normal operation of the circuit.
In the overcurrent state, when the current exceeds the rated value, the fuse heats up due to the resistance, and the temperature rises rapidly. Once it reaches the melting point, it melts and forms an open circuit.
After melting, the circuit is permanently cut off. It is necessary to manually replace the fuse. This method can completely isolate the fault and prevent the components from overheating and being damaged.
The melting speed is affected by factors such as environmental temperature, pad heat dissipation conditions, and current magnitude.
What should be considered when purchasing a chip-type fuse?
- The rated current should match the maximum operating current of the circuit and should leave a safety margin of 25% to 50%. For example, if the maximum current of the circuit is 0.8A, a fuse with a rated current of 1A can be selected.
- The rated voltage must be higher than the operating voltage of the circuit; otherwise, it may not be able to safely interrupt the current.
- Fusing characteristics: Select fast-fusing type or slow-fusing type based on the load type and startup characteristics. Choose fast-fusing type for protecting electronic chips, and slow-fusing type for motors or power supplies.
- Packaging dimensions should be consistent with the PCB design, while also taking into account heat dissipation and breaking capacity.
- Breaking capacity refers to the maximum fault current that an fuse can safely interrupt when it melts. For high-energy circuits, a fuse with high breaking capacity must be selected.
- Working environment: High temperature, high humidity and vibration environments can affect the performance of the fuse. Therefore, it is necessary to choose a model with better environmental resistance.
- International certifications such as UL, CSA, and IEC can ensure safety and reliability.