From robotics to automotive systems, motor control is a fundamental aspect of many industrial applications. To help ensure optimal performance and protection of motor control systems, accurate and efficient monitoring of current is necessary. In this blog, we will explore the differences between two commonly used components for current sensing in motor control systems: current sense resistors and Hall Effect sensors. This information is further detailed in a Bourns application note titled “The Difference Between Current Sense Resistors and Hall Effect Sensors for Motor Control Applications”.

Motor Control and Current Sensing:

Before we dive into a few of the highlights from the app note, it is helpful to understand the significance of current sensing in motor control. Current sensing plays a vital role in monitoring the electrical current flowing through the motor windings, providing valuable information for controlling speed, torque and ensuring the safety and protection of the motor and its surrounding components.

Current Sense Resistors Basics:

Current sense resistors are passive components that enable accurate current measurement based on the voltage drop across their resistance. These resistors have a low resistance value and are placed in series with the motor windings. The voltage drop across the resistor is proportional to the current flowing through it, which can be measured and used for motor control.

In the application note, knowledgeable Bourns engineers present the following key notes for use of current sense resistors in motor control applications:

1. Accuracy and Linearity: Current sense resistors offer good accuracy and linearity in current measurement, enabling precise control and monitoring of motor currents. Their resistance values, typically in the milliohm range, minimize power dissipation while providing a measurable voltage drop.
2. Power Dissipation: Since current sense resistors have a small resistance value, they dissipate some power as heat due to the voltage drop across them. Care must be taken to select resistors with appropriate power ratings and thermal management techniques to prevent overheating.
3. Simplicity and Cost-Effectiveness: Current sense resistors offer a straightforward and cost-effective solution for current sensing in motor control applications. They are easy to integrate into existing circuit designs and require minimal additional circuitry.

Fundamentals of Hall Effect Sensors: 

Hall Effect sensors, on the other hand, provide a non-intrusive method for current sensing in motor control. These sensors use the Hall Effect, which states that when a current-carrying conductor is subjected to a magnetic field perpendicular to the current flow, a voltage is generated across the conductor. This voltage is proportional to the current being sensed.

The application note emphasizes the following key notes for the use of Hall Effect sensors in motor control applications:

1. Isolation and Non-Intrusiveness: As they are non-contact sensors, Hall Effect sensors do not require direct electrical connection to the current-carrying conductor. This isolation provides electrical safety, reduced interference, and aids in simplifying the circuitry design.
2. Wide Dynamic Range: Hall Effect sensors can handle a wide range of currents, from low to high, making them suitable for various motor control applications. They are able to provide accurate measurements even at high current levels, enabling precise control and protection of motors.
3. Complexity and Cost Considerations: A downside of Hall Effect sensors is that they require additional circuitry, including signal conditioning, amplification, and temperature compensation. These are needed to convert the sensor’s output into a usable voltage or current. These additional components add to the complexity and cost of the overall sensing system, which may not meet a motor design’s size and budget goals.

Conclusions:

The information covered in “The Difference Between Current Sense Resistors and Hall Effect Sensors for Motor Control Applications” provides valuable insights into the distinct characteristics and considerations to be made when selecting between current sense resistors and Hall Effect sensors for motor control applications.

Current sense resistors offer simplicity, cost-effectiveness and high accuracy measurement, making them ideal current monitoring solutions for many motor control designs.