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Current sense resistors save board space with new config

Posted: 20 Sep 2005 ?? ?Print Version ?Bookmark and Share

Keywords:irc wirewound? film technologies division? current sense resistor? oar series? oar-tp?

Resistors with high current

TT electronics IRC Wirewound and Film Technologies Division has developed a "tight-pitch" version of its open air, metal element current sense resistor (OAR series) with ratings as high as 3W in a reduced PC-board footprint. These new OAR-TP series devices are designed to save board space in densely-packed power supply designs.

The new OAR-TP through-hole resistors offer a high current, flameproof alternative to conventional axial devices and flat chips for current-sense circuits, particularly in applications where space is at a premium. The resistor's footprint is reduced by extending the height of the device above the board, thus keeping the resistor element's "hot spot" safely off the PC-board while providing for increased air circulation under it, resulting in increased heat dissipation and cooler operation, explained the company.

The OAR-TP series resistors offer identical specifications to the OAR devices. These resistors are rated for 1W or 3W at 85C, with resistance values from 0.1? to 0.005?, with tolerances down to 1 percent. They feature temperature coefficient of resistance (TCR) values as low as 20ppm/C and inductance values in the single-digit nanoHenry range. The operating temperature range is -40C to 125C.

A lead-free, RoHS-compliant version is available, as is a low inductance version for high-frequency applications. Custom specifications are also available.

The flameproof OAR-TP resistors are constructed of a wire resistive element with welded copper leads to prevent solder wicking, which can change the device's resistance value in the circuit by as much as 30 percent, said the company.

The OAR-TP series resistors feature a reduced pitch, or spacing between the leads on the circuit board (with a corresponding increase in the board mounted profile), when compared to the standard OAR series devices. The OAR-TP has mounting centers of 5 mm or 7 mm, depending on resistance, resulting in a potential reduction of more than 50% for the OAR-1 device and 60% for the OAR-3.

The OAR-1TP measures 7(W)-by-7.8(H)mm, while the OAR-3TP offers a footprint of 7-by-32mm and 5-by-32mm, depending on resistance value.

Typical pricing for the OAR-TP series resistors ranges from 18 cents to 20 cents in quantities of 25,000. Delivery is from stock to 10 weeks.

- Gina Roos

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