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POWER & ENERGY EFFICIENCY

Fuses that blow safely New fuse technology designed specifically for electric vehicles helps meet stringent automotive reliability standards.

Electric

HANDBOOK

vehicles (EVs) and hybrid electric vehicles (HEVs) now use high-energy lithium battery systems. These power sources have spurred a need for a reliable means of protecting against catastrophic failures. Resettable devices are suitable for overcurrent conditions caused by transitory fault conditions, and the venerable “one-shot” fuse remains the best circuit option where fault currents can damage other circuits or systems. Moreover, the move toward small, distributed and embedded electronics has elevated the need for high-performance, miniature surfacemount fuses. Located under the vehicle’s dashboard in the fuse box, bladetype fuses are still a ubiquitous method for providing fault protection.

The monolithic structure of a SolidMatrix ceramic fuse (left) absorbs fault current and shows no external damage. There is visible damage on the conventional printed circuittype chip fuse (right).

However, automotive electronics, with its higher current ratings and shrinking space constraints, has driven the need for advanced surfacemount fuse technology. Now, newgeneration fuse technology has been designed to better meet automotive circuit protection needs. Solid body, or chip, fuses are used in a wide range of spaceconstrained applications with current ratings typically ranging from as low as 125 mA to several Amperes. These devices come in both slow-blow and fast-acting configurations. The two most common structures for solid body chip fuses are the multi-layer ceramic type and printed circuit style. The ceramic type offers distinct advantages over the more commonly used printed-circuit style fuse. Because of its monolithic structure, the ceramic fuse is capable of higher current ratings in a smaller package, has a wider operating temperature, and has stable operating qualities in extreme conditions. Additionally, its structure is less susceptible to

MONOLITHIC FUSE AFTER OVERCURRECT

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mechanical damage. The ceramic fuse has a co-fired monolithic structure with up to four layers of fusible material embedded within. In the printed circuit structure, the device is mainly comprised of an epoxy substrate and glass fiber (FR4). The fuse element is bonded to the surface of the pc board and coated with a protective polymer. A new advance in ceramic fuse technology is called the SolidMatrix ceramic fuse. This solid-body ceramic fuse’s patented, multi-layer construction provides excellent mechanical and thermal stability over a wide temperature range (-55 to +150°C). It is useful to compare how a SolidMatrix ceramic fuse and a conventional printed-circuit type fuse might behave when subjected to an over-current fault condition. The fuse element of the conventional printedcircuit board type fuse opens, but the high over-current fault condition can lead to surface melting, cracking and compromised mechanical integrity.

CONVENTIONAL FUSE AFTER OVERCURRENT

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11/3/17 4:38 PM

Power & Energy Efficiency Handbook November 2017  
Power & Energy Efficiency Handbook November 2017  

Power & Energy Efficiency Handbook November 2017 Efficient cooling for EV battery packs thanks to CFD Early warning for EMC problems