OEM & Lieferant - Ausgabe 1/2021

88 New Products and Markets Polymer Positive Temperature Coefficient (PPTC) resettable fuse products are popular overcurrent protection solutions because un- der fault conditions, the device’s resistance will rise exponentially and remain in a tripped state, providing continuous overcurrent pro- tection until the fault is removed. Once the fault is removed and the power cycled through, the PTC fuse will return to its normal low re- sistance state. Higher Ambient Temperature Effects on PPTCs One reason a wider protection selection is needed is that higher inrush current in in- creased ambient temperature conditions can cause PPTC nuisance tripping. PPTCs are ther- mally sensitive devices, and in these environ- ments, less current is required to heat up or melt a PPTC’s polymer material. This means special consideration should be taken to select the right PPTC device. Helping to solve this issue is that Bourns’ high- temperature PPTCs are constructed using a proprietary blend of high-melting point poly- mer materials and carbon-based conductive fillers to achieve high-reliability overcurrent protection performance with a reduced risk of nuisance tripping particularly tailored for high temperature environments. The proprietary conductive polymer formulation also provides an elevated level of resistance to commonly found oils, lubricants and solvents that can cause adverse effects in some industrial and transportation applications. Traditionally, designers have used standard temperature PPTCs for these applications, but have had to specify a PPTC with a higher cur- rent rating in order to account for the higher ambient operating temperature (and there- fore the lower amount of current required to trip the PPTC device). Thermal derating tables and graphs on data sheets help design- ers with this important consideration. With Bourns’ high temperature-rated PPTCs, the thermal derating effect is minimized allow- ing designers to more accurately specify the most appropriate PPTC for their application. This gives engineers an enhanced overcurrent protection solution, rather than having to de- sign in a “standard temp” PPTC with a higher current rating to counter-balance the effect of the higher ambient temperature. Bourns Expanding Line of High-temperature Rated Multifuse ® Products Inworkingwith its customers, Bourns realized a growing need for broader line of enhanced overcurrent protection solutions for applica- tions that may requiremore reliable protection at higher temperatures. Over the last several years, Bourns has continually expanded its line of Multifuse ® high-temperature rated surface mount PPTC resettable fuse products. The dif- ferent series offer customers additional foot- print options to accommodate smaller or larger board layouts, as well as various size options that can support higher or lower current and voltage ratings. Bourns’ expanded offering of 125 °C rated Multifuse ® polymer PTC devices is specif i- cally designed to provide robust, cost-ef- fective overcurrent and overtemperature protection across a variety of harsh envi- ronments where high ambient operating temperatures are prevalent and long-life re- liability is crucial. The wide range of models within the portfolio provides hold currents up to 1.75 A with maximum currents of 40 A and maximum voltages up to 42 VDC. This allows designers to more precisely specify overcurrent protection into certain harsh environment designs where operating tem- peratures may exceed 85 °C. Bourns’ PPTC devices also feature enhanced thermal derating performance compared to traditional consumer grade models, allowing engineers to design around higher trip current ratings at elevated operating temperatures. And, their compact SMD design gives design- ers enhanced flexibility in space-constrained layouts compared to equivalent radial leaded devices. Robust PPTCs Provide Reliable Overcurrent Protection in High Ambient Temperature Designs By Lee Bourns, Product Line Manager Overcurrent Protection & PTC Heaters at Bourns, Inc. Designers of today’s automotive systems and other applications that must operate in severe environments un- derstand the need to add overcurrent and overtemperature protection to their designs to maximize reliability and therefore uptime. However, as electronic content in vehicles continues to climb, designers now require a wider selection of robust protection solutions that can withstand higher ambient temperature conditions. Graphik: © ServiceXpert GmbH S H A R E Bourns’ expanded offering of +125 °C rated Multifuse® PPTC devices are designed to provide robust, cost-effective overcurrent/ overtemperature protection for applications where high ambient operating temperatures are prevalent and long-life reliability is crucial.