SMW / SMF Series Power Wirewound and Metal Film Chip Resistors

What are the SMW / SMF Series Power Wirewound and Metal Film Chip Resistors?

The SMW and SMF are surface-mount power chip resistors housed in a rectangular ceramic case that is non-flammable, resistant to melting even under severe overload conditions, and compatible with common cleaning solvents in accordance with MIL-STD-202 method 215 and IEC 60068-2-45. The shared ceramic enclosure gives both series their characteristic robustness against heat and humidity while maintaining excellent electrical insulation properties.

The two series differ in their resistive element technology. In the SMW, a resistive wire is wound in a single layer on a ceramic rod; metal caps are pressed over the rod and the wire ends are welded to the caps, producing a true wirewound element with the high surge and pulse-handling capability that construction implies. The SMF uses a metal film layer deposited over a high-grade ceramic rod, with leads welded to pressed metal caps in the same manner. This difference in element technology defines the resistance range each series can cover: the SMW spans 0.1Ω to 680Ω in 2W, 3W and 5W ratings, while the SMF extends from 10Ω to 2MΩ across the same power ratings, with maximum working voltages of 300V for the 2W variant and 500V for the 3W and 5W variants.

Both series are offered in tolerance grades of ±1% (F) and ±5% (J). The temperature coefficient of resistance is a maximum of ±200ppm/°C for the SMW and a tighter ±100ppm/°C for the SMF, reflecting the inherently more stable behaviour of the metal film element over temperature. The operating range extends from −55°C to +200°C for both series. Short-time overload performance is rated at five times the nominal power rating for five seconds, with resistance change limits of ±1.0% for the SMW and ±0.5% for the SMF. Long-term load life testing at 1,000 hours and moisture load life testing at 500 hours impose resistance change limits of ±2.0% and ±1.0% respectively.

The package design is optimised for seamless automatic surface mounting, featuring flexible tinned copper terminations and a fully welded internal construction that withstands the thermal stresses of reflow, vapour phase and infrared soldering processes. Components are supplied in tape and reel packaging for pick-and-place assembly, with reel quantities of 1,000 pieces for the 2W variant, 500 pieces for the 3W, and further configurations available for other power ratings. A thermal fuse variant for surge and inrush current protection is available upon request.

Model: SMW/SMF
Resistor type: Wire wound
Description: Power chip
Power Rating: 2W, 3W, 5W
Resistance (Ω): 0.1~680
Tolerance (%): ±1, ±2, ±3, ±5, ±10
TCR (ppm/C): 200

Model: RQA
Resistor type: Wire wound
Description: Ceramic encased
Power Rating: 5W~20W
Resistance (Ω): 0.1~100k
Tolerance (%): ±5, ±10
TCR (ppm/C): 260, 400

Model: FWR
Resistor type: Wire wound
Description: Fusible
Power Rating: 1W, 2W, 3W, 5W
Resistance (Ω): 0.1~200
Tolerance (%): ±5
TCR (ppm/C): 300

Model: RW
Resistor type: Wire wound
Description: Wire wound
Power Rating: 0.5W~10W
Resistance (Ω): 0.1~680
Tolerance (%): ±1, ±2, ±3, ±5, ±10
TCR (ppm/C): 260 max.

Model: PWR
Resistor type: Wire wound
Description: Precision wire wound
Power Rating: 0.5W~10W
Resistance (Ω): 0.1~100k
Tolerance (%): ±0.1, ±0.25, ±0.5, ±1, ±2
TCR (ppm/C): 20, 50, 90