 Providing power electronics design engineers with the means to squeeze more current-sensing capability into crowded power supply designs, TT electronics IRC Wirewound and Film Technologies Division has developed a ‘tight pitch’ version of their open air metal element current sense resistor with ratings as high as 3W in a reduced PC board footprint.
Designated the OAR-TP Series, these open-air through-hole devices offer a high current, flameproof 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.
“We developed this tight-pitch version of our proven OAR current sense resistor in response to requests from power supply design engineers,” explained David Winkler, product manager at IRC’s Wirewound and Film Technologies Division. “Devices with increased height improve cooling efficiency, and because many power supply designs are already tightly-packed at the PC board level, the additional height does not create any profile issues.
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 or 7 mm, depending on resistance, resulting in a potential reduction of more than 50% for the OAR-1 and 60% for the OAR-3. The OAR-1TP is .275″ in width by .300″ in height (7.0mm x 7.8mm); while the OAR-3TP is .275″ x 1.25″ (7.0mm x 32.0mm) and .197″ x 1.25″ (5.0mm x 32.0mm), depending on resistance value.
With identical specifications to IRC’s proven OAR Series devices, the OAR-TP Series resistors are rated for 1W or 3W at 85șC, with resistance values from 0.1? to 0.005?, with tolerances down to ±1%. They feature TCRs as low as ±20ppm/șC and inductance values in the single-digit nanoHenry range. Operating temperature range is -40șC to +125șC.
IRC will also produce OAR-TP Series resistors to customer requirements outside these standard electrical and mechanical specifications. A lead-free RoHS-compliant version is available, as is a low inductance version for high frequency applications. 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%.
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