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PCB Fuse: An Indispensable Part of the Electronics

In today’s electronics, protecting your circuit board from damage is one of the most vital steps. A tiny yet most powerful component, the PCB fuse, protects any circuit board. It breaks the circuit when through too much current. Like regular fuses, they prevent potential damage and fire hazards by melting their metal wires during an overload.
 
With the rapid development of science and technology, all kinds of products are getting smaller and more integrated.  So, comparing the new fuses and traditional fuses are completely different. For example, smartphone fuses must meet the trend of fast charging. They not only have to withstand instantaneous high currents but also have to function as protection. So now the PCB fuse requirements are getting higher and higher.

Whether designing, repairing, or maintaining a PCB, you must understand how to choose and use these fuses. In this blog, we will understand the essentials of PCB fuses and their role in safeguarding your electronics.

How Does Fuses Work

Before we discuss PCB fuses, let’s understand how fuses work first. Here is a video from YouTube for you to comprehend the principle of fuses.

As the video shows, a fuse is an electrical appliance that breaks a circuit when the current exceeds a specified value by fusing the fuse with the heat it generates.

When current flows through it, it generates heat, and its heat generation increases with time. The amount of current and resistance determines the rate of heat generation, and the construction of the fuse and its installation determines the rate of heat dissipation. If the heat generation rate is less than the heat dissipation rate, the fuse will not blow. If the heat generation rate is equal to the heat dissipation rate, the fuse will not blow for a long time. Similarly, if the heat generation rate is greater than the heat dissipation rate, more and more heat will be generated. Since it has a certain specific heat and specific mass, the increase in heat manifests itself as an increase in temperature. When the temperature rises above the fuse’s melting point, the fuse melts, and that’s how it works.

What is a PCB Fuse?

As mentioned earlier, fuses are primarily designed to protect equipment from overvoltages and currents that can cause malfunction and damage to the entire circuit board. As the same, a PCB fuse is a safety device that protects a circuit board (including its components) from overcurrents and other malfunctions.

Like regular fuses, PCB fuses are designed to break a circuit when the current exceeds the limits in the circuit board. They consist of a metal wire that melts when the current is too high. The fuse then breaks the electrical connection and interrupts the flow of the circuit. In short, it serves to protect not only against possible damage to other components but also against the risk of fire. After troubleshooting and resolving the overcurrent issue, you can replace the PCB fuse to restore possible circuit protection.

Types of PCB Fuses

PCB Fuses are designed for use on printed circuit boards, and they come in many types to meet different circuit protection needs. Below are some common types of PCB fuses:

Radial Lead Fuses

If you want to protect your circuit board, radial lead is one type of PCB fuse. They are compact and cylindrical, with two leads that extend from the bottom of the fuse body. They are easy to install and come in various current ratings. This fuse’s ceramic body type helps provide excellent insulation with better heat resistance capacity. It can be used widely in power supplies, the automotive industry, consumer electronics, telecommunications, and more.
 
The advantages are as follows:
  • The small size of the radio fuse makes it the best choice for applications where space is limited and circuits are dense.
  • You can install this fuse by just soldering it on the circuit board.
  • It supports the wide current ratings, making it the best option for various applications.
  • It can handle higher fault currents and protects the board’s components and connected devices.

Axial Lead Fuse

The axial lead fuse has the lead that extends from both sides of the cylindrical fuse body. It makes them suitable for horizontal mounting in PCB. The configuration provides better mechanical stability. While selecting the axial lead fuse, you need to consider the various factors including normal operating current, and maximum voltage time-current characteristics, which should match the requirements of specific applications. They are available in a wide range of current ratings that fit different design requirements. These fuses are commonly found in electronic appliances, automotive circuits, and other applications where space and reliability are critical factors.
 
The advantages are as follows:
  • The small size of the axial lead fuse makes it easier to integrate into space-limited devices.
  • They provide consistent performance and ensure reliable circuit protection.
  • They provide a cost-effective solution for the overcurrent protection.

Surface Mount Device Fuse

Surface Mount Devices are designed for surface mounting directly on the PCB, making them ideal for high-density circuit designs. This fuse is small, lightweight, and can handle a wide range of current ratings. SMD fuses are essential in modern electronic devices like smartphones, laptops, and tablets, where space conservation is crucial.
 
The advantages are as follows:
  • It offers reliable overcurrent protection, various sizes, and ratings to meet different application needs.
  • The compact size and compatibility with the automated assembly process make them a popular choice in advanced electronics manufacturing.

Pico Fuses

Pico fuses, sub-miniature fuses designed for low-current applications, are available in both radial and axial configurations. These small, cylindrical fuses are used in compact electronic devices with limited space.
 
Despite their small size, pico fuses provide reliable overcurrent protection and are available in various current ratings. They are commonly used in applications including handheld electronics, communication devices, and precision instruments. Pico fuses are designed to meet the stringent requirements of modern electronics, offering high performance in a tiny package.

Chip Fuses

Chip fuses are a type of surface-mount device (SMD) fuse designed for use on PCBs. They are compact and designed to fit into tight and narrow spaces, making them ideal for modern electronic devices where space is at a premium. Chip fuses provide reliable overcurrent protection and have a wide range of current ratings. They are commonly used in mobile devices, wearable technology, and other compact electronics. They are small and compatible with automated assembly processes. This makes them a popular choice for high-volume production. Chip fuses ensure the safety and reliability of electronic circuits in space-constrained applications.

Things to Consider While Choosing Right Fuse for PCB

You must consider various factors while selecting the right fuse for your PCB. So, let’s discuss some of the major factors to consider while choosing the right PCB fuse:
Ratings
Current Ratings
Try to select the fuse with a current rating slightly higher than the maximum operating current. This helps to protect against overcurrent.
Voltage Ratings
Ensure the fuse’s voltage rating meets the circuit’s maximum voltage. A fuse with lower voltage ratings will be useless.
Breaking Capacity
 
It is also known as the interrupting rating. It is the maximum current the fuse can safely interrupt without being destroyed. Thus, always choose a fuse with a breaking capacity higher than the potential fault current in your circuit.
Environmental Factors
 
Operational Temperature
Choose the ambient temperature in which the fuse will operate. The fuse can have various ratings at various temperatures and conditions. Thus, the fuse rating for high- and low-temperature environments must be checked.
Vibration and shock resistance
Regulatory and Safety Standards
 
Ensure the fuse complies with relevant regulatory standards such as UL (Underwriters Laboratories), IEC (International Electromechanical Commission), and other industry-specific standards. This ensures safety, reliability, and legal compliance.
Physical Size and Footprint
 
The fuse must physically fit within the PCB layout. Check the dimensions and mounting style, whether it’s surface mount or through-hole, to ensure compatibility with your board design.

Testing of PCB Fuses

There are various methods to test your PCB. Let’s check some of the common and simple methods to test PCB fuse below:

Visual Inspection

After installation, visually inspect the fuse and solder joints for defects and improper connections.

Continuity Test

Then, the multimeter can be used to test the continuity of the fuse. Place the multimeter probes on either end of the fuse. The multimeter will beep in case of fuse with no default and show a low resistance value. However, the multimeter will show an open circuit if the fuse is blown.

Current Test

Use an inline current meter or clamp meter to measure the current passing through the fuse. After connecting the circuit to its power supply, ensure the current falls within the predicted range. This might assist in confirming that the fuse is the right size and operates normally under typical operating circumstances.

Functional Test

If it’s safe and feasible, simulate an overcurrent situation to ensure the fuse blows as intended. This makes it easier to confirm if the fuse protects the circuit as needed.

The Difference Between PCB Fuses and Circuit Breakers

Fuses and Circuit Fuses are both used to provide overcurrent protection, but there are some key differences between them:
Item
PCB Fuse
Circuit Fuse
Mounting method
Designed for Surface Mount Technology (SMT), it can be soldered directly to the PCB and fit into compact spaces and the miniaturization needs of modern electronic devices.
It can be traditional glass tubes or ceramic fuses, usually used for mounting on circuit boards or in circuit boxes through holes, and are relatively large.
Physical form
PCB Fuse is usually smaller to fit into the compact layout of a PCB.
It may have larger physical dimensions, including different shapes and sizes to accommodate various circuit requirements.
Response time
PCB fuses may have faster response times because of their compact design, which is important for protecting sensitive electronic components.
Its response time may be slightly longer, but sufficient to handle higher power circuits.
Cost
PCB fuses may be less costly due to their small size and high level of integration.
It may cost more, especially for higher ratings or special fuses.
Application Scenarios
PCB Fuse is Commonly used in portable devices, consumer electronics, and high-density PCB designs.
It is used in industrial equipment, automotive circuits, and applications requiring higher current carrying capacity.

Conclusion

Knowing about PCB fuse is the most important step during PCB design, assembly, and repair. The fuse is small but still the most powerful device that protects your circuit board from overcurrent conditions. Thus, you must select the right PCB for your circuit, considering factors like voltage ratings, breaking capacity, regulatory standards, and more.
 
At FC PCBA, we specialize in providing high-quality PCBs, ensuring proper and reliable circuit board protection. Our experts have many years of experience selecting and integrating the right PCB for optimal performance and safety.
Contact us today to learn how we can help you design and manufacture a PCB based on your specific requirements. Let FC PCBA be your manufacturing partner and happily provide all PCB-related services.

FAQs

You can check the fuse to see if it’s blown out. Check the wire inside the glass. If it has a break or any dark and burnt appearance, then the fuse is definitely blown out.
The next method is to use the multimeter to check the continuity of the fuse. If there is no continuity, then it’s confirmed that the fuse is blown out.
PCB repair involves fixing damaged components or connections on the PCB. This can include:
 
  1. Component Replacement: Replacing faulty or damaged components like capacitors, resistors, or ICs.
  2. Trace Repair: Fixing broken or damaged conductive traces on the board.
  3. Soldering: Re-soldering loose or broken connections.
  4. Testing and Diagnostics: Using tools like multimeters and oscilloscopes to diagnose and ensure proper functionality of the PCB after repairs.
A fuse is a one-time protection device. It melts and breaks and can’t be used again, while circuit breaks can be rested and resided even after the tripping.
Usually, fuses have a faster response time as compared to circuit breakers. You can find fuses in small electrical devices and circuit breakers in industrial and home electrical systems.
Common issues in fuse include overloading, poor solder joints, aging, mechanical stress, and environmental factors.

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