The Wirewound and Film Technologies Division of IRC Inc. (Boone, NC), a subsidiary of TT electronics plc, developed a "tight pitch" version of its open-air, through-hole, metal element, current sense resistor with ratings as high as 3 W in a reduced PC board footprint. The new OAR-TP Series offers a high current, flame-proof alternative to conventional axial devices and flat chips for current-sense circuits where PC board 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, and providing for increased air circulation under it, which in turn provides increased heat dissipation and cooler operation.
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 percent for the OAR-1 and 60 percent for the OAR-3. The OAR-1TP measures 0.275 in x 0.300 in (7.0 mm x 7.8 mm) while the OAR-3TP is 0.275 in x 1.25 in (7.0 mm x 32.0 mm) and 0.197 in x 1.25 in (5.0 mm x 32.0 mm), depending on resistance value.
With identical specifications to IRC’s OAR Series devices, the OAR-TP Series resistors are rated for 1 W or 3 W at 85 ºC, with resistance values from 0.1 Ω to 0.005 Ω, and tolerances down to ±1 percent. The devices feature TCRs as low as ±20 ppm/ºC and inductance values in the single-digit nanoHenry range. The operating temperature range is from –40 ºC to +125 ºC.
The flameproof OAR-TP Series 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. Pricing for the OAR-TP Series resistors ranges from $0.18 to $0.20 in quantities of 25,000. Lead times are from stock to 10 weeks.
