Shunt Resistors Information

Last revised: December 05, 2024

Reviewed by: Scott Orlosky, consulting engineer

Shunt resistors are connected in parallel with an instrument or component to divert electrical current. They provide an alternate path for current in case of failure, and can be used to accomplish a reduction in input sensitivity from the input line to ground. Current shunt resistors are low resistance, passive electronic devices used to measure alternating current (AC) or direct current (DC) by the voltage drop those currents create across the resistance. Electrical specifications for shunt resistors include ohms, resistance tolerance, current rating, power rating, temperature coefficient of resistance, and power coefficient of resistance. Ohms measure a material’s opposition to the flow of electricity in a circuit. Temperature coefficient of resistance (TCR) refers to the change in resistance with change in temperature. Power coefficient of resistance (PCR) is the temperature rise caused by self-heating. For current-sensing shunts, resistances typically range from 100 µOhms to 500 milliOhms. Low TCR and PCR are important. For shunt resistors used in current conversion applications, high precision may be required.

Physical Specifications

Physical specifications for shunt resistors include mounting style, lead type, and resistor material. Shunt resistors can be bolted, chassis mounted, surface mounted, or through-hole mounted. Chassis-mounted resistors attach to a metal surface for maximum heat dissipation. Surface mount technology (SMT) and through-hole technology (THT) are other common mounting styles. Lead types include: axial leads, gull-wing leads, J-leads, radial leads, screw terminals and tab terminals. Shunt resistors without leads are also available. Choices for shunt resistor material include: carbon film, ceramic, metal alloy, metal film, metal oxide, thick film, thin film, and wire wound. Carbon shunt resistors are made of a mixture of finely-ground carbon and insulating material held together by a resin binder. Ceramic shunt resistors are made of solid, high-temperature, ceramic, resistive materials with bonded metal contacts. Metal alloy shunt resistors contain two or more metallic elements. Wire wound shunt resistors are made by winding thin wire onto a ceramic rod.

Packing Methods

Shunt resistors differ in term of packing method. Some passive electronic components are packed in tape reel assemblies that include a carrier tape with embossed cavities for storing individual components. Others are packed in trays (rails) and are made of carbon-powder or fiber materials and molded into rectangular outlines that contain matrices of uniformly spaced pockets. These containers protect components during shipping and provide proper component location and orientation for use with industry-standard, pick-and-place board assembly equipment. Shunt resistors that are packed in shipping tubes, stick magazines, or bulk packs are also available.

Shunt Resistors FAQs

How do different types of shunt resistors vary in terms of their features and applications?

Shunt resistors are essential components in electrical circuits, used primarily for current measurement by creating a voltage drop across the resistor. Different types of shunt resistors vary in their features and applications based on their construction, material, and specifications. Here's a breakdown of some of the key types and their characteristics:

Surface Mount Shunt Resistors: These resistors offer low milliOhm values (0.5 to 1.0 m?), small package size, and low inductance (less than 2 nH). They are AEC-Q200 qualified, indicating high reliability under temperature cycling, shock, vibration, and moisture resistance.

Applications: Suitable for high-current applications (up to 100 A) and can be mounted on direct bonded copper (DBC) or insulated metal substrate (IMS) power substrates.

Thick Film Shunt Resistors are known for supporting higher power levels, these resistors are often used in consumer and industrial applications.

Low-Value Shunt Resistors are available in very low resistance values (200 μΩ to 2 mΩ) with a power rating of 5 W. They can handle currents over 150 A and are designed for harsh environments.

They are used in automotive, industrial, and medical applications where large currents need to be sensed.

Metal Element and Shunt Resistors: These resistors provide high stability in very low resistance values and can handle high currents, sometimes up to 1,200 A. They are commonly used to measure current output in circuits.

What are the advantages of using thick film shunt resistors in industrial applications?

Thick film shunt resistors offer several advantages in industrial applications, primarily due to their ability to support higher power levels.

Thick film shunt resistors are designed to handle higher power levels, making them suitable for demanding industrial environments where robust performance is required.

These resistors are known for their durability, which makes them suitable for industrial settings where equipment is often exposed to harsh conditions. Their construction allows them to maintain performance over time, even under stress.

Thick film technology allows for a wide range of resistance values and power ratings, providing flexibility in design and application. This versatility makes them applicable in various industrial scenarios.

Compared to some other types of resistors, thick film resistors can be more cost-effective, offering a balance between performance and price, which is advantageous for large-scale industrial applications.

The construction of thick film resistors aids in effective thermal management, which is essential in applications where heat dissipation is a concern.

These characteristics make thick film shunt resistors a popular choice in applications where high power, reliability, and cost-effectiveness are critical considerations.

What is the construction of thick film shunt resistors?

Thick film shunt resistors are a type of resistor known for their ability to handle higher power levels. Generally, thick film resistors are constructed by applying a resistive film onto a ceramic substrate, which allows for a wide range of resistance values and power ratings. This construction method contributes to their durability and reliability in harsh environments.

How do thick film shunt resistors compare to other types of resistors in terms of performance?

Thick Film Shunt Resistors are known for their ability to support higher power levels, making them suitable for demanding environments.

Metal element shunt resistors can handle very high currents, sometimes up to 1,200 amps, providing high stability in very low resistance values.

Surface mount shunt resistors, like the BVN 1216 series, are AEC-Q200 qualified, indicating high reliability under temperature cycling, shock, vibration, and moisture resistance.

Low-value shunt resistors, such as the LRMAP3920 series, are designed for harsh environments and can handle large currents, making them versatile for automotive, industrial, and medical applications.

Thick Film Shunt Resistors: Generally more cost-effective compared to some other types, offering a balance between performance and price

Overall, thick film shunt resistors are particularly useful in applications requiring high power handling, durability, and cost-effectiveness. However, other types of resistors, such as metal element and low-value shunt resistors, may offer superior performance in specific application areas like current precision and stability.

What are the differences between surface mount and through-hole shunt resistors?

Surface mount and through-hole shunt resistors differ in their mounting styles and associated characteristics. Here's a detailed comparison based on the information available:

Surface mount shunt resistors are designed to be mounted directly onto the surface of a printed circuit board (PCB). They do not require holes to be drilled into the PCB, which can save space and allow for more compact circuit designs.

Through-hole shunt resistors have leads that are inserted into holes drilled in the PCB and soldered on the opposite side. This method provides a strong mechanical bond, making them suitable for applications where the resistor might be subject to physical stress

Surface mount shunt resistors are typically smaller in size, allowing for more components to be placed on a PCB. This is advantageous in applications where space is limited, such as in compact electronic devices.

Through-hole shunt resistors are generally larger due to the need for leads and the space required for drilling holes. They are less space-efficient compared to surface mount resistors.

While they offer good electrical performance, surface mount shunt resistors may not be as mechanically robust as through-hole resistors, especially in environments with significant vibration or mechanical stress.

The design of surface mount resistors, such as the BVN 1216 series, aids in airflow around the resistive element, which helps in effective thermal management.

Through-hole shunt resistors often have different options for heat dissipation due to the larger size and the ability to attach to heat sinks or other cooling methods.

What is the thermal management of surface mount shunt resistors?

The design of surface mount shunt resistors, such as the BVN 1216 series, includes a metal heat sink that channels flow across the top of the resistor. This helps in dissipating heat more effectively, which is essential for maintaining the resistor's performance and reliability under high power conditions.

Surface mount shunt resistors can be mounted on direct bonded copper (DBC) or insulated metal substrate (IMS) power substrates. These substrates are known for their excellent thermal conductivity, which helps in spreading and dissipating heat away from the resistor, thereby enhancing thermal management.

The temperature coefficient of resistance (TCR) is an important factor in thermal management. For example, the BVN 1216 series has a TCR of less than 50 parts per million per degree Celsius, which indicates that the resistance value changes minimally with temperature fluctuations. This stability helps provide accurate current measurement and reliable performance over a wide range of conditions.