Top 10 circuit-protection devices
Manufacturers of circuit-protection devices have significantly improved the performance of their safety components to protect electronic devices and equipment from a range of failures caused by electrical surges and electrostatic discharge (ESD), as well as overvoltage, overcurrent, and overtemperature conditions.
At the same time, manufacturers of circuit-protection devices such as fuses, transient-voltage suppressor (TVS) diodes, and varistors have focused on providing more packaging options, particularly surface-mount variants in smaller sizes. These more compact designs help to improve assembly and reduce costs by enabling designers to switch from through-hole to surface-mount packaging.
Here is a selection of 10 circuit-protection devices, introduced over the past year, that not only deliver enhanced performance but also tackle the need to streamline assembly and reduce printed-circuit-board (PCB) space.
Fuses
Littelfuse Inc. launched its NANO2 415 SMD Series Fuse last year, targeting space-constrained applications. The fuse is designed to provide true buffering for 250-V applications with unpredictable voltage fluctuations.
The NANO2 is the company’s first surface-mount fuse with a 1,500-A interrupting rating at 277 V, safeguarding against unpredictable surges. (The device is a 2025 Electronic Products Award Winner.)
The SMD fuse allows designers to replace through-hole devices, which helps to reduce production costs and streamline assembly processes. It also enhances surge-withstand and pulse-withstand capabilities with higher I2t values than competitive solutions, according to the company.
The NANO2 415 SMD Series is an SMD alternative to the through-hole Littelfuse 215 Cartridge Series, offering a higher voltage rating (277 V, versus 250 V). These fuses can be used in a range of applications, including consumer electronics, appliances/white goods, home automation, industrial systems, and automotive.
For 12-V power rails in servers, data centers, and telecom infrastructure, Alpha and Omega Semiconductor Ltd. (AOS) offers the AOZ17517QI series 60-A eFuse, designed to integrate accurate analog current- and voltage-monitoring signals. This current-limiting-protection eFuse monitors and protects critical power rails in data centers and telecom infrastructure to protect the main power bus from interruption due to abnormal load under fault conditions.
The eFuse leverages AOS’s advanced co-packaging technology that combines a high-performance IC with protection features and the company’s latest high-safe-operating-area (SOA) Trench MOSFET. The AOZ17517QI series’ MOSFET offers low, 0.65-mΩ on-resistance that isolates the load from the input bus when the eFuse is off. Key specs include an operating voltage range of 4.5 V to 20 V and a 27-V absolute maximum rating.
Other features include programmable soft-start, startup SOA management, and other protection circuitry, including programmable overcurrent protection, short-circuit protection, undervoltage lockout, overvoltage clamp, and thermal shutdown protection.
Multiple eFuses can be used in parallel for higher-current applications. Multiple devices can operate concurrently and distribute the current during the startup phase. The series is available in two versions: the AOZ17517QI-01 (auto-restart) and AOZ17517QI-02 (latch-off), both housed in a 5 × 5-mm QFN-32L package.
If you’re looking for greater options in a fuse family, Bourns Inc. expanded its Multifuse MF-LSMF polymeric positive-temperature-coefficient (PPTC) resettable fuse line with nine new models. This series now offers a wider hold current and increased voltage. The new fuse models provide hold currents up to 7 A and voltage up to 72 V, with select models in SMD packaging.
The entire MF-LSMF fuse line leverages the company’s freeXpansion technology that boosts performance by incorporating higher hold currents, increasing voltages, and enhancing resistance stability in a compact footprint. These features enable the fuses to protect low-DC-voltage ports in USB, IEEE 1394, and powered Ethernet IEEE 802.3af ports.
These fuses shield against overcurrent and overtemperature events within the specified parameters. They are suited for low-voltage telecom equipment, industrial control, security systems, and portable electronics.
In addition, the MF-LSMF Series’ SMD terminals are manufactured with electroless nickel immersion gold plating for greater component reliability and longevity. This is in comparison with the nickel-tin plating commonly used for competitive fuse terminals, which are susceptible to issues such as whisker formation, oxidation, and corrosion and can cause fuse short-circuits, according to Bourns. The devices are RoHS-compliant and halogen-free.
Another fuse family designed to provide more options for designers is Vishay Intertechnology Inc.’s S2F and S3F series of thin-film chip fuses in three package sizes (0402, 0603, and 1206).
The Vishay Sfernice S2F and S3F devices ensure circuit continuity with minimal resistance and reliable interruption under overload conditions. They provide options for fast- or very fast-acting protection. Applications include secondary circuit protection across a broad range of electronic systems in which stability and precision are critical.
The fuses are UL 248-14–compliant and cover rated currents from 0.315 A to 7 A. Both series combine low resistance with body temperature rise below 75°C at 100% rated current.
The key distinction between the two series is their fusing speed at 200% overload. The fast-acting S2F series is designed to open in less than one minute, while the very fast-acting S3F series is designed to open in less than five seconds. The S2F series provides protection where brief overloads are tolerable without immediate interruption, while the S3F series is optimized for sensitive circuits that require the quickest possible response, Vishay said.
These options enable designers to tailor fuse performance to the specific protection needs of their applications. The devices are lead-free, halogen-free, and RoHS-compliant.
TVS devices
Semtech Corp. recently expanded its SurgeSwitch family with the TDS5311P protection device as an alternative to conventional TVS diodes. Described as the industry’s first circuit-protection device to deliver near-constant clamping voltage for USB Power Delivery (PD) Extended Power Range (EPR) applications at 48 V, the TDS5311P protects power buses operating at up to 53 V. It is purpose-built for USB PD EPR systems operating at 48 V across industrial equipment, rugged mobility devices, and high-performance portable systems.
Designers face a protection gap at 53 V, Semtech said: “Conventional TVS diodes clamp inconsistently, with clamping voltage shifting across current levels and temperature ranges.”
In comparison, the TDS5311P is reported to maintain a nearly constant clamping voltage from the first microsecond of a surge event through maximum rated current, across the full −40°C to 125°C industrial temperature range.
The TDS5311P, built on the SurgeSwitch’s surge-rated FET architecture, handles 1,512-W peak pulse power and 24-A peak pulse current. It meets the IEC 61000-4-5 industrial surge standard. The protection device is housed in a small, 2.0 × 2.0-mm DFN-6 package.
Also claiming improvements over traditional solutions, Littelfuse has introduced the 5.0SMDJ-FB series of TVS diodes to protect sensitive electronic equipment from voltage transients caused by lightning and other transient-voltage events. The series delivers up to 15% lower clamping voltage over traditional solutions and maintains breakdown voltage above the reverse standoff voltage. This ensures reliable protection for sensitive downstream components such as next-generation DC/DC converters.
The lower clamping voltage via Littelfuse’s foldback technology enhances circuit-protection performance in TVS components, including I/O interfaces, VCC bus, and other vulnerable circuits used in telecom, computer, industrial, and consumer electronic applications, specifically for power over Ethernet systems, AI and data center servers, ICT equipment power supplies, and industrial DC power distribution.
The 5,000-W surface-mount solution in a DO-214AB package provides protection in harsh environments. The operating junction temperature range is −65°C to 150°C. It is a drop-in replacement for the legacy 5.0SMDJ Series with the same compact DO-214AB (SMC) footprint. It meets IEC 61000-4-2 ESD 30 kV (Air) and 30 kV (Contact) and is recognized to UL 497B as an isolated loop circuit protector.
Microchip Technology Inc. recently introduced its JANPTX family of non-hermetic plastic TVS devices that meet the MIL-PRF-19500 qualification for high-reliability protection in aerospace and defense applications.
These surface-mount TVS devices are claimed as the first in the industry to achieve MIL-PRF-19500 qualification in a plastic package. This packaging offers a lightweight (0.25 grams), cost-efficient solution while meeting stringent military performance requirements.
The JANPTX product line is available in voltage ranges from 5 V to 175 V and offers several variants:
- JANPTX1N5555UJ
- JANPTX1N5558UG
- JANPTX1N5629AUJ
- JANPTX1N5665AUG
- JANPTX1N5907UG
- JANPTX1N5907UJ
The JANPTX family protects sensitive electronic components in demanding environments with a high peak pulse power rating of 1.5 kW and clamping response times measured at less than 100 picoseconds in internal tests. They are designed for surface-mounting and protect against voltage transients such as lightning strikes, ESD, and electrical surges.
The advanced design of these surface-mount, unidirectional TVS devices supports protection from switching transients, induced RF effects, electromagnetic pulse, and secondary lightning events and meets IEC61000-4-2, IEC61000-4-4, and IEC61000-4-5 standards. Applications include airborne avionics, electrical systems, and other mission-critical applications in which low voltage and high reliability are essential.
Taiwan Semiconductor Co. Ltd. expanded its automotive-grade 24-V Super Clamp TVS diode series with its first compact SMC/SMB surface-mount devices. Super Clamp TVS diodes provide ultra-low clamping voltage and high surge current in space-constrained automotive designs.
The Super Clamp snapback devices provide lower clamping voltages, higher peak pulse currents, and lower voltage ratings than conventional TVSes, according to the company. This allows circuit designers to use fewer, less costly components without impacting circuit reliability.
In addition, the new devices—SMC (LSMC24CAH) and SMB (LSMB24CAH)—offer package options that can help reduce PCB space. The complete TVS series is offered in three package types: the DO-214AB (SMC), DO-214AA (SMB), and DO-218AB.
When used in compact, surface-mount PCB layouts, Super Clamp TVSes can reduce part count and eliminate the need to overdesign to achieve automotive-level reliability. The TVS devices, with maximum pulse currents of up to 300 A, provide a margin of system protection much higher than alternative options, according to the company. They are also reported to provide higher protection than MOVs and GDTs, which are subject to failure after repetitive transients.
Varistors
Kyocera AVX recently released high-temperature, automotive-grade multilayer varistors (MLVs) for 48-V power supply systems. The new addition to the TransGuard VT Series, claiming the first in the industry to offer MLVs rated for 175°C operation, supports operating temperatures extending from −55°C to 175°C with zero derating across the entire range. They are qualified to AEC-Q200, IEC 61000-4-2, and ISO 10605.
The TransGuard VT Series MLVs are zinc oxide–based, ceramic semiconductor devices that offer reliable, bidirectional overvoltage protection and EMI/RFI attenuation capabilities in compact SMT packages that reduce the need for discrete MLCCs. They offer high current- and energy-handling capabilities, multi-strike capabilities, and low leakage.
The TransGuard TVS devices meet the highest human-body model ESD classification, at Class 6, which means they can reliably withstand over 25,000 V of ESD, Kyocera said. They also have the lowest moisture-sensitivity level, at MSL 1, providing an unlimited floor life under the specified conditions. It also means they don’t require any special dry packing or handling procedures and don’t need to be baked before reflow soldering.
The new 48-V System VT Series MLVs are designed for motor vehicles with 48-V power supplies, rated for operating temperatures up to 150°C, and additionally qualified to VDA-320. The devices are available in five EIA chip sizes (0805, 1206, 1210, 1812, and 2220) and rated for 56-VDC or 40-VAC working, 100- to 110-V clamping, 48-V jump start, 30 to 1,500 A, and 0.2- to 9-J transients. The capacitance ranges from 80 to 2,800 pF. Applications include electric vehicles, including e-bikes, e-scooters, golf carts, and passenger and commercial vehicles, as well as their charging stations.
Several TransGuard VT Series MLV part numbers, including a few of the 48-V System VT Series MLVs, are also available with the company’s FlexiTerm terminations, which can withstand severe vibrations, up to 5 mm of mechanical board flexure, and up to 3,000 temperature cycles extending to 150°C without any internal cracking, exceeding the AEC-Q200 testing requirement of 1,000 cycles at up to 125°C.
TDK Corp. has introduced the MT40 series of ThermoFuse varistors (B72240M) for surge protection of up to 50 kA. They target applications such as inverters, industrial power supplies, outdoor lighting, telecommunications systems, and surge-protection devices.
TDK calls the MT40 series a new generation of surge-protection components (SPCs), with a compact design and advanced safety features thanks to their patented overmolding technology and integrated thermal disconnecting system. These SPCs provide protection up to 50 kA in a compact package size of 38.0 × 15.2 × 40.9 mm.
Designed for extreme electrical conditions, the MT40 series offers a peak surge-current capability of up to 50 kA (8/20-μs pulse) and a short-circuit current rating of up to 200 kA. The series is recognized as a UL 1449 Type 1CA component assembly, which means they can be used in applications with AC voltages ranging from 150 V to 550 V and DC voltages from 200 V to 750 V.
Other features include a galvanically insulated, normally open micro-switch for remote monitoring and an optional visual indicator. The operating temperature range is −40°C to 85°C. They are RoHS-, REACH-, and PFAS-compliant.
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