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PCB fuses, also known as current fuses, are basic safety devices widely used in circuits for overcurrent protection. Their primary function is to protect power electronic equipment from damage caused by overcurrent or overheating. When a fuse is properly installed in a circuit, if the current abnormally increases, causing the fuse material to heat up to its melting point, it will safely blow and interrupt the current, thereby preventing unsafe phenomena such as combustion, arcing, or explosions, and ensuring the safe operation of the circuit.
What is the difference between PCB fuses and circuit breakers?
PCB fuses and circuit breakers have very similar functions—they both interrupt the circuit during sudden current surges or short circuits. However, there is a key difference. Circuit breakers are switches, and like all switches, they can be re-engaged once disconnected. Most PCB fuses, on the other hand, can only be used once. Once they blow, they must be replaced. This is a design weakness.
Fuses are inexpensive, can be quickly and easily replaced, and result in minimal downtime. It is important to install the correct rated current and fully compatible model for the equipment. This number indicates the current level the fuse can handle before it blows.
There are other relevant metrics. The speed rating indicates how quickly the fuse blows when the current exceeds the rated value; more sensitive fuses are a safer choice. Voltage drop refers to voltage loss caused by cable impedance—essentially, the voltage at the end of the cable is lower than at the starting point. If the loss is too significant, some low-power devices may not function properly. It is also important to check the energy released when the fuse blows. Excessive energy may damage the equipment or even pose a safety hazard.
PCB fuses Classification:
Based on different operating mechanisms and application scenarios, PCB fuses can be categorized into the following types:
1. Conventional fuses: When the current in the circuit exceeds its rated value, the fuse blows, thereby interrupting the circuit. This type of fuse is typically used to protect circuits from damage caused by overcurrent and overheating.
2. Fast-acting fuses: Compared to fuses, fast-acting fuses have faster response times and shorter melting times. These fuses are typically used in applications requiring rapid circuit disconnection, such as automotive circuits and industrial automation.
3. Magnetic core fuses: Magnetic core fuses use magnetic fields to control current levels, thereby protecting circuits. These fuses are commonly used in applications requiring precise current control, such as motor protection and transformer protection.
PCB fuses parameters:
Ambient temperature: This refers to the air temperature directly surrounding the fuse and should not be confused with room temperature. In many practical applications, the temperature of the fuse can be quite high, as it is often installed in enclosed spaces (e.g., mounted on a fixed bracket in a distribution panel) or near other heat-generating components such as resistors or transformers.
Current characteristics: The rated ampere rating is marked on the fuse. This value represents the current the fuse can carry, determined under a series of controlled test conditions.
Derating factor: At 25°C ambient temperature, we recommend that the operating current of the fuse should not exceed 75% of the rated current value, as this rated current value is determined under controlled test conditions. Fuses are temperature-sensitive components, and their parameters are determined at an ambient temperature of 25°C. The temperature of the fuse increases or decreases with changes in ambient temperature when current flows through it.
Fuse performance specifications: The performance of a fuse in terms of design refers to how quickly it responds to various current loads, typically categorized into three types: ultra-fast-acting, fast-acting, and slow-acting.
Fuse structure: The internal structure varies depending on the ampere rating.
Fusing rated capacity: Also known as the breaking capacity or short-circuit rated capacity. The fusing rated capacity is the maximum permissible current that the fuse can reliably interrupt at the rated voltage. During a short circuit, the fuse experiences multiple transient overcurrent surges exceeding its normal operating current. Safe operation requires the fuse to remain intact (without bursting or breaking) and to eliminate the short circuit.
Resistance: The resistance of the fuse is also very important in the overall resistance of the circuit. Since the resistance of fuses with an ampere rating less than 1 is only a few ohms, this factor should be considered when using fuses in low-voltage circuits. Most fuses are made of materials with a positive temperature coefficient (PTC), so we often refer to cold resistance and thermal resistance (voltage drop at rated current).
Welding precautions: Since most fuses have welded joints in their structure, extreme caution should be exercised when installing these fuses using welding methods. Excessive heat during welding can cause the solder inside the fuse to flow back, altering its rated value. Fuses are thermally sensitive components similar to semiconductors, so it is recommended that users use heat-absorbing devices when welding fuses.
Voltage rating: The voltage rating marked on the fuse indicates that the fuse can safely and reliably interrupt its rated short-circuit current in a circuit where the voltage is equal to or less than its rated voltage. For most small-sized fuses and miniature fuses, the standard voltage ratings are 32V, 125V, 250V, and 600V.
Fuse selection and application
When selecting a fuse, the following factors should be considered:
1. Rated current: Select a fuse with a rated current suitable for the circuit to ensure it functions properly and provides adequate protection.
2. Temperature rating: Choose a fuse with an appropriate temperature rating based on the circuit's operating temperature range to ensure it functions properly in high-temperature environments.
3. Installation method: Select a fuse with an appropriate installation method based on the circuit's specific requirements, including surface mount, through-hole, or soldered types.
In applications, fuses can be used in various circuits, including power supply circuits, motor drive circuits, lighting circuits, etc. By correctly selecting and using fuses, circuits can be effectively protected from damage caused by overcurrent and overheating, thereby extending the service life of the circuit.
Troubleshooting PCB fuses:
When a fuse malfunctions, it must be promptly addressed to ensure the safe operation of the circuit. The following are some common methods for troubleshooting fuse issues:
1. Check if the fuse is properly installed: If the fuse is not properly installed or has poor connections, it may fail to function normally. Therefore, before troubleshooting, it is necessary to inspect the installation of the fuse.
2. Check if the fuse has blown: If the fuse has blown, it must be replaced with a new one. When replacing the fuse, it is important to select a new fuse with the same rated current and temperature rating as the original fuse.
3. Check the circuit for overloading or short circuits: If there is overloading or a short circuit in the circuit, it may cause the fuse to blow or burn out. Therefore, before troubleshooting, it is necessary to check the circuit for overloading or short circuits.
4. Check other components in the circuit: If other elements in the circuit are faulty, it may also cause the fuse to blow or burn out. Therefore, before troubleshooting, it is essential to verify that all other components in the circuit are functioning properly.
Summary
PCB fuses are commonly used electronic components that protect circuits from damage caused by overcurrent and overheating. When selecting and using fuses, factors such as the circuit's rated current, temperature rating, and installation method must be considered. Additionally, it is important to understand PCB fuse troubleshooting methods to promptly address issues and ensure the safe operation of the circuit.