In today's increasingly complex electronics landscape, protecting circuits from power surges, short circuits, and other electrical hazards is more important than ever. One of the simplest yet most effective ways to safeguard sensitive components is by using electronic fuses. But what exactly are electronic fuses, and how can you implement them effectively in your designs? This blog will explore the significance of electronic fuses, their working principle, and how to integrate them into circuits for optimal protection.
What Are Electronic Fuses?
Electronic fuses are protective devices designed to limit the flow of current in a circuit. When the current exceeds a preset threshold, the fuse will "blow," interrupting the power supply and preventing further damage to the circuit. Unlike traditional glass or ceramic fuses, electronic fuses offer more precise control over current levels, and in many cases, they can reset themselves once the fault condition is resolved. These fuses play a crucial role in protecting sensitive electronic components such as semiconductors, capacitors, and integrated circuits (ICs), which can be easily damaged by overcurrent or voltage spikes.
Why Use Electronic Fuses?
1. Prevent Damage to Sensitive Components
Modern electronics often involve delicate components that cannot tolerate high current levels. Integrated circuits (ICs) and microchips, for instance, are highly sensitive to fluctuations in power. Excessive current can cause overheating, circuit failure, or even permanent damage. Electronic fuses provide a reliable defense by cutting off excessive power before it can harm these components.
2. Overcurrent Protection
Overcurrent situations arise when too much electrical current flows through the circuit. This can occur due to a short circuit, a sudden surge in power, or component failure. In such scenarios, electronic fuses act as an automatic disconnect, preventing the current from causing more significant issues. The fuse can either blow or activate a switching mechanism that interrupts the circuit until the issue is addressed.
3. Increased Reliability and Longevity
By using electronic fuses, the overall reliability and lifespan of an electronic system are significantly improved. These fuses can handle high fault currents and protect against irregular power conditions that would otherwise shorten the life of sensitive parts, reducing the need for costly repairs or replacements.
4. Compact and Cost-Effective
Unlike traditional mechanical fuses that may require additional space or external protection mechanisms, electronic fuses are compact and integrate seamlessly into most designs. Their low cost and small size make them ideal for consumer electronics, automotive applications, and industrial machinery.
5. Resettable Options
One of the major advantages of electronic fuses over traditional ones is their resettable nature. After an overcurrent event, some electronic fuses can be automatically reset or manually reset after the issue is fixed. This feature reduces downtime and maintenance costs compared to traditional fuses, which need to be physically replaced once blown.
How Do Electronic Fuses Work?
The principle behind an electronic fuse is relatively simple. Electronic fuses typically use a combination of electronic switches and sensors to monitor the current flow through the circuit. When the current exceeds a preset value, the fuse activates an interrupt mechanism, either turning off a power switch or sending a signal to a control unit to shut down the circuit.
1. Current Monitoring
The fuse continuously measures the current in the circuit. When it detects an increase in current that surpasses the predetermined limit, the fuse triggers the protective mechanism.
2. Signal Processing
Some electronic fuses are equipped with microcontrollers or integrated circuits that handle signal processing. The signal is interpreted to determine whether the event is a transient or a sustained overcurrent situation. In cases of sustained overcurrent, the fuse acts to disconnect the circuit.
3. Interrupting the Circuit
The fuse then disconnects the power supply by either turning off a transistor, opening a relay, or triggering another switch that cuts off the excessive current from the circuit. In more advanced designs, the fuse can automatically reset after a certain amount of time or once the overload condition is cleared.
How to Choose the Right Electronic Fuse for Your Circuit?
When selecting an electronic fuse, it’s essential to consider several factors to ensure that it will provide adequate protection for your sensitive circuits.
1. Current Rating
The first consideration is the current rating of the fuse. Choose a fuse with a rating just above the normal operating current of your circuit to avoid nuisance tripping during minor current spikes, but low enough to protect your components from potentially damaging overcurrent conditions.
2. Response Time
The response time of a fuse is critical. Some circuits may experience rapid current surges that need to be addressed almost instantly, while other circuits may handle brief overcurrent conditions without damage. Select a fuse with a response time that matches your circuit’s tolerance to power spikes.
3. Voltage Rating
Ensure that the voltage rating of the fuse is higher than the maximum voltage your circuit will experience. If the voltage rating is too low, the fuse may not be able to handle the conditions in your application, leading to failure.
4. Resettable vs. Non-Resettable
Depending on your needs, you can choose between resettable fuses (such as PTC fuses) and non-resettable ones. Resettable fuses are more convenient for devices that are prone to occasional surges, while non-resettable fuses may be better for applications where a one-time fault condition is more likely.
5. Form Factor and Size
Ensure that the fuse you choose is compatible with the physical size and layout of your circuit. Electronic fuses come in various packages, from surface-mount devices (SMD) to through-hole versions.
How to Integrate Electronic Fuses into Your Circuit Design?
Integrating electronic fuses into your circuit design is relatively straightforward. Here are the steps to follow:
• Determine Fuse Placement
Place the fuse in series with the power supply line. It should be located as close to the power source as possible to ensure that it can effectively cut off the current in case of a fault.
• Select the Appropriate Fuse Type
Based on your circuit's characteristics (current, voltage, and fault conditions), choose the right fuse type (e.g., PTC or traditional electronic fuse) and rating.
• Incorporate Control Mechanisms
If you're using a resettable fuse, you may want to integrate a control system that monitors the health of the fuse and alerts the user when a fault has occurred. This is especially important in high-reliability systems like medical or automotive electronics.
• Test the Circuit
After incorporating the fuse, test the circuit under various fault conditions to ensure that the fuse activates as expected. It’s critical to ensure that the fuse does not interfere with normal operation, and that it reacts correctly to overcurrent situations.
Picking an eFuse: Functions and applications
When choosing an eFuse, there are some basic parameters to consider. The top-tier consideration is, not surprisingly, the current level at which the fuse acts. This typically can range from under 1 ampere (A) up to about 10 A, as well as the maximum voltage the fuse can withstand across its terminals. For some eFuses, this current level is fixed, while for others it can be user set via an external resistor. Other selection factors include response speed, quiescent current, size (footprint), and the number and type of external support components needed, if any. In addition, designers must consider any additional features and functions the different eFuse models may offer.
For example, PLCs are an application where eFuses are beneficial in different subcircuits that may be prone to sensor I/O and power misconnection. There are also current surges as wire connections are made or boards are hot swapped. An eFuse such as the Texas Instruments TPS26620 is often used in these 24 volt applications. It is shown set for a 500 mA limit in Figure 2. It operates from 4.5 volts to 60 volts at up to 80 mA, with a programmable current limit, overvoltage, undervoltage, and reverse polarity protections. The IC can also control inrush current and provide robust protection against reverse current and field miswiring conditions for both PLC I/O modules and sensor power supplies.
The timing diagrams in Figure 3 for Toshiba’s TCKE805, an 18 volt, 5 A eFuse, show how one vendor has implemented the auto-retry versus latched modes. In auto-retry mode (set by the EN/UVLO package pin), the overcurrent protection function prevents damage to the eFuse and its load by suppressing power consumption in the event of a fault situation.
If the output current, set by external resistor (RLIM), exceeds the limit current (ILIM) value due to a load error or short circuit, the output current and output voltage decrease, thereby limiting the power consumed by the IC and the load. When the output current reaches the preset limit value and overcurrent is detected, the output current is clamped so that no more current than ILIM flows. If the overcurrent situation is not resolved at this stage, this clamped condition is maintained and the eFuse temperature continues to rise.
When the eFuse temperature reaches the operating temperature of the thermal shutdown function, the eFuse MOSFET is switched off, stopping the flow of current entirely. The auto-retry operation attempts to restore the current flow by stopping the current, which lowers the temperature and releases the thermal shutdown. If the temperature rises again, the cycle repeats and stops the operation until the overcurrent situation is eliminated.
In contrast, latch mode clamps the output until the eFuse is reset via the Enable (EN/UVLO) pin of the IC (Figure 4).
Some eFuses can be configured to overcome issues associated with current sensing across a resistor, such as the associated IR drop which reduces the output-side rail voltage. For example, the 3.3 volt STEF033AJR from STMicroelectronics has nominal maximum current and FET on-resistance values of 3.6 A and 40 milliohms (mΩ), respectively, for the DFN package; and 2.5 A and 25 mΩ for the flip-chip package. In the conventional connection shown in Figure 5, at higher current values, even a modest IR drop of about 15 millivolts (mV) in the supply rail through the on-resistance may be significant and worrisome.
Modifying the conventional connection by putting the resistor between the positive-side limit connection and the output voltage connection (VOUT/Source), implements a Kelvin-sensing arrangement that compensates for the IR drop (Figure 6).
Note that although eFuses are semiconductors and can work down to single-digit voltages, they are not limited to that low region. For example, eFuses in the Texas Instruments TPS2662x family are rated for operation from 4.5 to 57 volts.
Conclusion
Electronic fuses are an essential tool in protecting sensitive circuits from overcurrent and other electrical hazards. Their ability to protect delicate components, reduce maintenance costs, and enhance the overall reliability of a circuit makes them indispensable for modern electronic design. By understanding the different types of electronic fuses and how they function, you can make informed decisions about their integration into your systems and ensure the longevity of your devices.
Whether you’re designing consumer electronics, industrial machinery, or automotive systems, including electronic fuses in your circuit design is a smart, cost-effective, and reliable way to protect your investment in sensitive electronic components.
Written by Icey Ye from AIChipLink.
AIChipLink, one of the fastest-growing global independent electronic component distributors in the world, offers millions of products from thousands of manufacturers. Whether you need assistance finding the right part or electronic components manufacturers for your design, you can contact us via phone, chat or e-mail. Our support team will answer your inquiries within 24 hours.
