Top ten harsh environment resistors

Source: Electronic Products article

By Gina Roos, Electronic Products select 10 top resistors designed for harsh environments, including automotive and industrial applications.

Fixed resistor manufacturers face continued demand for extended operating temperature ranges and AEC-Q200 qualified parts for automotive and industrial applications that need high stability in harsh environments. At the same time, a continuing trend towards miniaturization poses an additional challenge as manufacturers try to pack more performance in smaller package sizes.

Also, over the past several years, there has been a greater need for anti-sulfur resistors. Sulfur contamination was primarily an issue for the automotive industry but it has become a more widespread challenge in other application areas. Sulfur contamination impacts the reliability of resistors in high-sulfur content environments, which can cause product failures.

Here are 10 resistor lines introduced this year that deliver high reliability, high stability, or high temperature performance for a range of applications that require more robust performance.

Bourns, Model CRxxxxA-AS anti-sulfur resistors

Bourns Inc. offers a family of thick-film resistors that are designed to operate in harsh environments with a higher level of sulfur contamination. The Model CRxxxxA-AS chip resistor series is manufactured using a thick-film element printed on a ceramic substrate and tested in accordance with ASTM B809-95 methods, which tests for the porosity of metallic coatings exposed to humid sulfur vapor.

Bourns said the sulfur-resistant resistors had approximately 20 times greater operating lifetime than the standard device.

Model CRxxxxA-AS devices can be used in a range of applications, from general purpose to industrial (industrial motor controls, pump controls, and welding equipment) and outdoor and on-road applications (lighting and traffic control).

The AEC-Q200 compliant resistors are available in eight different footprints from 0201 (0603 metric) to 2512 (6432 metric) case sizes with rated power from 0.05 W to 1 W. The resistance values range from 1 ohm to 20 Mohms. The expanded line of resistors are RoHS compliant and halogen free. The operating temperature range is -55°C to 125/155°C.

KOA Speer, SR73-RT series current sense resistors

As end products continue to shrink, requiring smaller and smaller components, KOA Speer Electronics has added a 0402 case size to its SR73-RT series of low-resistance, anti-sulfuration current sense resistors. The SR731E-RT is available in ±1%, ±2%, and ±5% tolerances with resistance values from 1 ohm up to 10 ohms, and a power rating of 1/8 watt (W). The operating temperature range is -55°C to 155°C.

The current sense resistors use a special high sulfuration-proof inner top electrode material, which makes it suited for harsh environments with a high level of sulfur contamination. Applications include mining, automotive, factory automation, agriculture, oil/gas, and wine making. The resistors are AEC-Q200 qualified for automotive applications.

KOA Speer, RN73R series metal film chip resistors

KOA Speer Electronics launched its high-reliability RN73R series metal film chip resistors to meet high heat and high moisture applications, such as those found in automotive electronics, industrial equipment, and medical devices. They also can be used as gain adjustment resistors for OP amp circuits, and dividers for power-supply voltage monitors.

The resistors deliver improved electrolytic corrosion resistance and high stability compared to KOA’s existing RN73 thin-film resistors. The RN73R offers excellent heat tolerance with an operating temperature range of -55°C to 155°C and a rated ambient temperature of 85°C, as well as improved moisture tolerance of 85% for 1,000 hours at 85°C.

The RN73R resistors are offer power ratings (per case size) of 0.063 W (0402), 0.1 W (0603), 0.125 W (0805), and 0.25 W (1206) with a resistance range of 10 to 1.5 Mohms, resistance tolerances ranging from ±0.05% to ±1% and temperature coefficient of resistance (TCR) values of ±5, ±10, ±25, ±50, and ±100 ppm/°C. The resistors are RoHS compliant.

Riedon, BR series wirewound resistors

Riedon Inc. expanded its line of high-power wirewound resistors with the new BR series of rugged metal-clad braking resistors that target industrial and commercial applications such as motor drives, power conversion systems, HVAC systems, and battery charging and monitoring applications.

The BR series, encased in aluminum, are available in three different mechanical constructions and offer a power rating range from 60 W to 500 W. These rugged resistors provide excellent heat transfer and reduce the need for heatsinking. “They are also significantly less sensitive to heatsink requirements than a comparable TO-packaged device of a similar power rating, many of which may require a cold plate to operate at the same rated power,” said Riedon.

The company attributes the resistors’ high level of performance to the use of ceramic cores instead of fiberglass. Ceramic offers higher efficiency by handling heat more effectively during overload and current surge events.

The resistors are available in flat (BR) or tall (BRT) series versions with quick-connect terminations. They offer a resistance range from 0.1 ohm to 1 kohm with tolerances of 1%, 5%, and 10%; a withstand voltage of 2,500 VAC, and good long-term stability with a TCR of less than ±260 ppm maximum. The operating temperature range is –55°C to +200°C.

An ultra-slim version, the BRS series, also is available. Offering a 12-mm profile, the series offers power ratings from 100 W to 500 W and a resistance range from 1 ohm to 5 kohms.

Stackpole Electronics, RTAN Series tantalum nitride chip resistors

Stackpole Electronics’ RTAN tantalum nitride chip resistors offer robust humidity withstanding for applications that need precision resistance with long-term stability and reliability, and environmental robustness. These precision resistors withstand biased humidity testing at 85°C, 85% relative humidity, and 10% rated power with very little resistance shift.

The RTAN series are designed with anti-sulfur materials and passes the ANSI/EIA-977 (method A) standard sulfur test. The series also is AEC-Q200 compliant. It’s available in popular resistance values with 0.1% tolerance and 25-ppm TCR in 0805 and 1206 packages from stock. See the datasheet for the full range of case sizes, resistance values, TCR, voltage, and power ratings.

Applications include instrumentation, aerospace, test equipment, industrial controls, portable communications diagnostic equipment, and portable medical devices.

Stackpole Electronic, HVAM precision resistors

For applications that call for high precision, ultra-high stability, Stackpole Electronics offers the HVAM axial-leaded resistors. These high-voltage resistors are available in high resistance values of 10 Mohm, 100 Mohm, 500 Mohm, 1 Gohm, and 10 Gohm values with power ratings from 2 W to 10 W. The operating temperature range is -55°C to 225°C.

Parts include:

The HVAM20 with a 2-W power rating at up to 15 KV
The HVAM36 with a 3.6-W power rating at up to 15 KV
The HVAM50 with a 5-W power rating at up to 20 KV
The HVAM75 with a 7.5-W power rating at up to 30 KV
The HVAM100 with a 10-W power rating at up to 50 KV

A proprietary direct film deposition process enables the HVAM to achieve tolerances down to 0.1% and TCRs as low as ±50 ppm, while providing high-voltage ratings. These devices can be used in a variety of medical applications, circuit protection, voltage dividers, welding and plasma cutting equipment, and high-voltage power supplies.

TT Electronics, HDSC chip resistors

TT Electronics offers a unique chip resistor, a high-energy, double-sided (HDSC) resistor that is untrimmed for improved pulse performance. As part of its pulse withstanding resistor line, the HDSC chip resistors are designed for protection and discharge in industrial and medical applications. These include power supplies, circuit breakers, and medical monitor input protection applications where a 5% tolerance is suitable.

These anti-sulfur resistors provide better surge voltage and pulse power for enhanced surge protection in small, surface-mount designs. This also translates into enhanced reliability and reduces field failures in applications exposed to electrical surges like connected health and Industry 4.0 applications. They can withstand up to 6.5 kV peak for a 1.2/50 µs surge and up to 6 kW for a 0.1 ms pulse. The operating temperature range is -55°C to 155°C.

The HDSC resistors are available in four sizes from 0805 to 2512 and can be used to replace large chip or multiple chip solutions. The small footprint for given ratings saves printed-circuit-board (PCB) area for applications that call for a compact design.

TT Electronics, EBW8518 busbar-mounted shunt resistor

TT Electronics offers its E-Beam welded shunt resistors for industrial and automotive applications. The EBW8518 is an electron-beam welded resistance element that is sandwiched between large copper terminals with optional tin plating. Suited for precision applications, the resistors offer 1% tolerance, 100 ppm/°C TCR, 1 µV/°C thermal EMF, and separate ground pins to reduce errors.

The electron-beam welded technology and low thermal EMF make the shunt resistors particularly suited for hybrid electric vehicle (HEV) battery management, energy metering, and welding power supplies. They are AEC-Q200 qualified.

The EBW8518 provides resistance values from 50 microohms to 250 microohms. The low measurement error frees up the designer’s error budget and its low ohmic values reduces power loss, said TT Electronics. It also features low self-heating, which reduces equipment temperature and improves reliability for designers needing to manage temperature rise in compact power electronic assemblies, said the company.

Vishay, Power Metal Plate current sense resistors

The automotive-grade Power Metal Plate current sense resistors from Vishay Intertechnology, Inc. are designed for harsh environments, ranging from automotive and industrial to downhole instrumentation and HVAC systems. The WFM resistors eliminate the need to run multiple resistors in parallel, which can cause current measurement errors. By using a single high-power resistor, it improves power density that translates into space savings on the board.

The WFM resistors offer 2-W and 3-W power ratings in 2010 and 2512 case sizes. The resistors feature a solid metal manganese-copper or nickel-chromium alloy resistive element with a low TCR of < 20 ppm/°C, low inductance values of 0.5 nH to 5 nH, and low thermal EMF to < 3 µV/°C. The operating temperature range is -65°C to 170°C. The devices are RoHS-compliant, halogen-free, and Vishay Green.

The WFM devices incorporate an improved thermal management design using a copper heat spreader that allows the resistors to maintain its electrical characteristics of the Power Metal Plate construction. Vishay also uses a proprietary processing technique that enables a wide range of low resistance values from 5 mohms to 500 mohms, with tolerances down to ± 1.0%.

The devices are suited for a wide range of current sensing and pulse applications. These include automotive electronic controls, brushless DC motor controls, and battery management for electric and hybrid vehicles. They also can be used in high power inverter/converter controls and large motor drives for industrial applications; power supplies for downhole instrumentation; inverter control for consumer appliances and HVAC systems; and power management, conversion, and safety in servers and other computing applications.

Vishay, WSBS Power Metal Strip shunt resistors

Vishay also offers a shunt resistor for tough environmental conditions. The WSBS8518…34 and  WSBS8518…35 Power Metal Strip shunt resistors are manufactured with a solid metal nickel-chrome alloy resistive element with a calibration notch and “boot” design on their terminals. This improves TCR performance (down to ± 10 ppm/°C) for better accuracy over temperature extremes. Applications include battery management in gas, diesel, hybrid, and electric cars and trucks, as well as electric forklifts, large UPS systems, and other heavy industrial applications.

The Vishay Dale Power Metal Strip resistors, offered in an 8518 case size and an all-welded construction, offer very low resistance down to 100 microohms thanks to a proprietary technique and power ratings up to 36 W. The resistors feature a proprietary processing technique that produces their extremely low resistance values, which allow for high current capabilities.

The WSBS8518…34 and WSBS8518…35 offer low inductance values of <5 nH, low thermal EMF down to <1.25 μV/°C, and an operating temperature range of -65°C to +170°C. The resistors are RoHS-compliant, halogen-free, and Vishay Green.