Bourns Shunt Resistors Offer Accuracy, Stability for High-Power Apps

The ever-evolving power electronics landscape continually demands components that enhance efficiency and ensure reliability under varying operational conditions. For example, as the industry progresses, a significant trend is the rising demand for components that can handle high power while maintaining accuracy in current sensing. This is particularly important for applications like battery management systems and motor drives, which rely on accurate current sensing for proper operation.

 

The new shunt resistors from Bourns. Image used courtesy of Bourns

 

To this end, Bourns recently released four high-power shunt resistors for current sense applications. This article details the new products and explains how they benefit high-power applications.

 

Addressing High-Power Challenges

Current sense resistors are pivotal in power electronics, offering a simple yet effective way to measure current. Also known as shunt resistors, these devices are extremely low-resistance components that work by being placed in series with a load. A known resistance value and a measurable voltage drop across the component can determine the load’s current from a simple Ohm’s law calculation (V=I/R).

However, designing these resistors to handle high power in compact sizes without compromising accuracy poses significant challenges. Key factors include thermal management, resistance stability, and the temperature coefficient of resistance (TCR). TCR is a measure of how much a resistor changes value with temperature. In applications that require extremely accurate measurements, a low TCR is necessary.

 

Shunt resistors in series with a load. EEPower

 

Bourns Model CSI Series, including models CSI2H-2512, CSI2H-3920, CSI2H-5930, and CSI4J-4026, are designed to tackle these challenges. They feature ultra-low ohmic values, essential for high-power applications, and a low TCR, ensuring accuracy over a wide temperature range. Notably, they consist of electron beam welded resistive material coupled with a copper alloy construction, contributing to their long-term stability and low thermal electromotive force​.

Moreover, the varied footprints and the availability of two- and four-terminal models cater to different design needs. The four-terminal models, for instance, allow for precise four-wire Kelvin resistance measurements, which is crucial for accurate current sensing in sensitive applications.

 

Product Focus: CSI2H-2512

One of Bourn’s new offerings worth highlighting is the Model CSI2H-2512.

This series ranges in resistance range/power rating from <0.1 mΩ /100 A to 3.5 mΩ/4 W. While the power rating is specified at 70°C, the devices are rated to operate in a range from -55 to 170°C. The TCR, on the other hand, is rated to be between ±75 PPM/°C to ±150 PPM/°C, depending on the model. Other notable specifications include a resistance tolerance as low as ±1% and an inductance less than 2 nH, depending on the material type.

According to the company, the device’s environmental characteristics are rigorously tested to ensure reliability under various conditions. For example, it withstands thermal shock from -55 to +150°C for 1000 cycles, indicating its capability to operate reliably through extreme temperature changes. Additionally, the component's resilience to short-time overload (5 times rated power for 5 seconds) and resistance to soldering heat (+260°C for 10 seconds) are critical for maintaining integrity during unexpected power surges and manufacturing processes. 

 

Characteristics of model CSI2H-2512. Image used courtesy of Bourns

 

Overall, its ability to endure high-temperature exposure (+170 °C for 1000 hours) and low-temperature storage (-65 °C for 24 hours) indicates its durability and long-term reliability in various operating environments.

 

High-Power Resistor Takeaways

Bourns anticipates its new devices will be used in applications such as battery management systems, switched-mode power supplies, and motor drives. As power electronics continue to evolve, components like these will likely play a crucial role in driving innovations, ensuring reliability, and meeting the stringent requirements of various applications.