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Rugged open air resistor handles high power dissipation

Posted: 30 Aug 2007 ?? ?Print Version ?Bookmark and Share

Keywords:rugged resistor? open air? high power dissipation?

OARS resistors

TT electronics Welwyn Components has developed the open air current senses (OARS) resistor series. The low-ohm resistors are designed to solve thermal issues common in automotive and industrial electronics.

The series features a resistive element with a unique open air 'flow through' design that keeps the resistor's 'hot spot' safely off the PCB and allows air to circulate around it, contributing to cooler operations through increased heat dissipation.

As a surface mount device, the OARS Series resistors have compliant terminations that allow them to expand and contract with the PCB's thermal cycling, enabling them to meet or exceed the 1,000-2,000 cycles required by most automotive manufacturers. This thermal cycling stresses the solder joints of conventional flat chip resistors, which can often cause failure. The lead form of the OARS resistors provides an inherent advantage in compliance to the mechanical stress caused by thermal cycling. The welded copper terminals in the OARS Series also provide a low-resistance terminal to enhance reliable performance for demanding applications.

The OARS Series resistors are rated for 1W at 85C (2W at 25C) with resistance values from 0.002 to 0.05 with tolerances down to 1 percent. They feature TCRs as low as 20ppm/C and inductance values in the single-digit nanohenry range. Operating range is -40C to 125C.

TT electronics Welwyn Components has also developed a wider version of its OARS resistor with a higher power rating than conventional metal element resistive devices. Designated the OARS-XP Series, the resistor features a wider metal alloy resistive element that offers exceptional TCR ratings and superior thermal compliance.

The resistors' form factor provides designers with several advantages. The wider resistive element enables higher current to pass through the device and the open air design provides a far cooler operation by allowing more air flow under the resistive element to keep heat from being transmitted to the PCB.

The distinctive form of the product also provides the inherent ability to flex slightly and provide stress relief during extreme temperature cycling on FR4 or metal substrates.

Resistance values for the OARS-XP Series range from 2m to 50m, with standard tolerances of 1 percent and 5 percent. Inductance values are less than 10nH, with operating temperature ranges from -40C to 125C. All OARS series parts are RoHS compliant and zero-ohm jumper versions are also available.

The OARS Series also features bimetallic construction with welded copper terminals that aid solderability and resistance measurement reliability. Applications include automotive motor control, power supply and process monitoring.

- Henri Arnold
EE Times Europe

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