Product News: Electronic Components & Devices
Current Sense Resistors offer TCR of ±2 ppm/°C.
Press Release Summary:
July 18, 2014 - Providing power ratings from 1.5 W in free air to 80 W when mounted in heatsink, Powertron S Series offers resistance from 0.002–50 Ω and tolerances to ±0.1%. Devices feature max currents to 150 A, thermal EMF of <1 µV/°C, and temperature range of -40 to +130°C. Delivering load life stability of ±0.1% after rated power at 70°C for 2,000 hr, RoHS-compliant precision foil resistors are suitable for power supplies, digital multimeters, medical equipment, AC/DC converters, and battery chargers.
Original Press Release
VPG's New S Series Precision Foil Current Sense Resistors Combine Low TCR Down to ±2 ppm/°C with High Power Ratings to 80 W
Press release date: July 10, 2014
The resistors released today offer a wide range of power ratings — from 1.5 W in free air to 80 W when mounted on a heatsink — with low resistance values from 0.002 Ω to 50 Ω and tight tolerances to ±0.1%. The devices feature maximum currents to 150 A, with higher values available upon request; very low inductance; thermal EMF of <1 µV/°C ; and a temperature range of -40 °C to +130 °C.
Providing exceptional load-life stability of ±0.1% typical after rated power at 70°C for 2,000 hours, S Series resistors provide highly accurate and reliable current sensing in power supplies, digital multimeters, current control systems, medical equipment, solar and wind inverters, AC/DC converters, and battery chargers. The RoHS-compliant devices are available in a wide range of package sizes, including the standard TO-220 and surface-mount version.
"Several years ago Powertron decided to focus on developing resistive current sense devices with Kelvin connections that would allow quick and accurate current measurements," said Yuval Hernik, senior director of application engineering for VFR. "Current sensing circuits provide the data control that circuits need to operate properly, and foil resistors are among their fundamental building blocks. In the typical application, a controlling circuit monitors current flowing through a current sense resistor as a voltage drop across the resistor and directs parameter changes to ensure that optimum circuit performance is maintained."
Every current sense resistor must have an error budget assigned to it. If this budget is exceeded, equipment will fall out of its performance specification, or possibly fail. In addition to initial tolerance, the error budget includes allowable shifts through shelf life, assembly, TCR, shock, vibration, thermal shock, thermal EMF, and load-life drift. Designers then need to select a particular resistor technology with the least amount of change through all the stresses, add up all the expected Rs, and subtract these from the end-of-life tolerance limit to arrive at the purchase tolerance. This needs to be kept in mind when considering the overall long-term costs of a system, and the consequences of attempting to save on upfront assembly costs. Precision current sense resistors with the same resistance, tolerance, and TCR — but of different technologies — are not interchangeable, as the changes through their service life are not the same. Substitution on the basis of these alone could jeopardize performance and mission success.
"Today we see more and more attempts by certain electronic manufacturing services to replace precision current sense resistors with cheaper solutions that put system performance at risk," added Hernik. "Designers utilizing current sense resistors for critical applications should demand specific data from their suppliers to be certain that the resistors are exactly what are needed. The data should cover the resistance values required by the circuit as much as possible, and one should not assume that all resistors of a particular style, configuration, or technology have the same implied reliability."
Device Specification Table
|Type||Resistance range (Ω)||Power rating (W)||Max. current (A)|
|Free air 70 °C||With heatsink|
|SHR 4-2321||0.005 to 20||3||40||150|
|SHS 4-4618Q||0.005 to 50||3||50||150|
|SHR 4-3825||0.0005 to 60||3||50||150|
|SNR 4-T227||0.002 to 20||-||80||100|
|SPR 4-T220||0.005 to 10||1.5||15||50|
|SPR 4-T221||0.005 to 10||1.5||15||50|
|SPR 4-T227||0.002 to 20||-||60||100|
|SPR 4-3316||0.005 to 50||2||-||-|
Samples and production quantities of the S Series current sense resistors are available now, with lead times of seven to eight weeks. Pricing starts at $4.67 per piece in 100-piece quantities.
VPG is an internationally recognized designer, manufacturer and marketer of components based on its resistive foil technology; sensors; and sensor-based systems specializing in the growing markets of stress, force, weight, pressure, and current measurements. VPG is a market leader of Foil Technology Products, providing ongoing technology innovations in precision foil resistors and foil strain gages, which are the foundation of the company's Force Sensors Products and its Weighing and Control Systems. The product portfolio consists of a variety of well-established brand names recognized for precision and quality in the marketplace. To learn more, visit VPG at www.vpgsensors.com.
Powertron is a brand of VPG Foil Resistors, which produces the most precise and stable resistors available. Powertron develops, manufactures and markets high-precision foil, current sense, and thick film resistors for use in diverse applications and offers a full complement of resistors for accurate, precise, and high-power circuits, with customization capabilities supporting virtually any package type. Powertron focuses on delivering solutions with the best combination of power ratings, TCR, and resistance ranges with foil resistor products that include devices built on CuNiMn Bulk Metal® Foil for low-ohm, high-precision applications, and NiCr foil for even higher levels of stability. A thick film product line is also available in a wide range of packages. Further information is available at www.powertron.de.
Bulk Metal is a registered trademark of VPG.