Vitreous-enamelled resistors toughen up modern electronic controls

In addition to protecting the resistor, thereby promoting stable performance, the impervious coating also allows the W20 series to operate at temperatures up to 375°C and so to deliver high power ratings in relation to body size. For example, the W24, which has a nominal power rating of 14W, has an 8.0mm-diameter axial-leaded body of length 53.5mm. The resistors can also withstand overloads up to 25 times rated power for 1 second.

Vitreous-enamelled resistors such as the W20 series meet the requirements of modern automotive subsystems such as cable harnesses, which must be impervious to contaminants, and ECUs exposed to high temperatures in the engine bay or close to the exhaust or transmission. The impervious coating also allows use in electronic systems deployed in harsh industrial environments, such as systems exposed to sulphur-bearing exhaust gases. When used in domestic heating-control units, superior pulse performance helps designers meet high market expectations for lifetime reliability.

In addition to these emerging applications, vitreous-enamelled resistors such as the W20 series continue to be the power resistor of choice in applications such as military and aerospace equipment needing CECC-approved parts, power supply inrush current limiting, active discharge of reservoir capacitors, and dummy load banks in test fixtures.

The W20 commercial series comprises five sizes with nominal power ratings of 3W, 5W, 7W, 10W and 14W, and with voltage ratings from 100V to 750V. Resistance values from 1 ohm to 100k ohms are available in E24 values, and typical TCR is ±75ppm/°C. Device families certified to CECC 40-201-002 are designated JB, HB, KB, LB, MB, and are rated from 2.9W to 14.0W.