How to choose fuses (technical section)

The selection of fuses requires comprehensive consideration of circuit parameters, usage environment, and safety requirements. The following are the key steps and precautions for selection:
1. Determine key parameters
(1) Rated Current
Normal operating current: The rated current of the selected fuse should be slightly higher than the maximum continuous operating current of the circuit.
Conventional experience: Rated current=1.25~1.5 times the working current (higher if there is surge current in the circuit).
Example: The maximum operating current of the circuit is 2A, and fuses ranging from 2.5A to 3A can be selected.
Surge current: If there is a startup surge in the circuit (such as a motor or switch power supply), a * * Time Delay * * fuse should be selected to avoid accidental melting.
(2) Rated Voltage
The rated voltage of the fuse must be ≥ the maximum operating voltage of the circuit.
Example: For a 24V system, at least select a fuse with a rated voltage of 24V or higher.
(3) Breaking Capacity
Breaking capacity refers to the maximum fault current (such as short-circuit current) that a fuse can safely cut off.
Low voltage low current circuit: Optional glass tube fuse with lower breaking capacity.
High voltage/high current circuits: ceramic tubes or high breaking surface mount fuses with high breaking capacity should be selected.
2. Choose the fuse characteristic
Fast Acting:
Suitable for protecting sensitive devices such as ICs and LEDs, with fast response speed.
Typical scenarios: data cables, low-power power supplies.
Time Delay:
Allow short-term surge current to pass through to avoid accidental triggering.
Typical scenarios: motors, switching power supplies, capacitive loads.
3. Environmental factors
Temperature impact:
The rated current should be reduced by 5% to 10% for every 10 ℃ increase above 25 ℃ in high-temperature environments.
Example: A fuse rated at 3A may need to be used at 2.5A in an environment of 50 ℃.
Vibration/Shock:
Anti vibration fuses (such as axial lead packaging) should be selected for high vibration environments.
4. Physical dimensions and packaging
Surface mount type: suitable for occasions with compact PCB space (such as 0603, 1206 packages).
Plug in type: used for power input terminals of automobiles and industrial equipment (such as ATO and ATC series).
Tubular type: suitable for high-power or high-voltage scenarios (such as 5 × 20mm glass tube fuses).
5. Certification and Standards
Select certified fuses according to the application field:
Consumer electronics: UL/CE certification.
Automotive Electronics: AEC-Q200 or ISO 8820.
Industrial equipment: IEC 60127。
Summary of Selection Steps
1. Determine circuit parameters: maximum operating current, voltage, surge current.
2. Choose the fuse characteristic: fast break or slow break.
3. Calculate the rated current: consider temperature derating and margin.
4. Matching breaking capacity: Select according to the fault current.
5. Choose packaging and certification: Combine installation methods and industry standards.

matters needing attention
Safety margin: Avoid the rated current approaching the circuit limit value.
Convenience of replacement: Choose an easily replaceable package (such as a pluggable fuse holder).
Prohibited from using beyond specifications: Low voltage fuses should not be used as a substitute for high voltage models, even if the current matches.

By following the above steps, it can be ensured that the fuse is reliably blown in case of overcurrent or short circuit, while avoiding misoperation or safety hazards.