Introduction

Current sense resistors are critical components in electronic circuits, enabling precise current measurement for power management, battery monitoring, motor control, and overcurrent protection. These resistors, also called shunt resistors, provide a voltage drop proportional to the current flowing through them, allowing systems to monitor and regulate power efficiently.

In this blog, we’ll explore:

• • How current sense resistors work

  • Key parameters for selection

  • Common applications

  • Best practices for PCB layout

How Current Sense Resistors Work

A current sense resistor is placed in series with a load, and the voltage drop across it (per Ohm’s Law, V = I × R) is measured to determine the current. Since the resistance value is known, a small voltage measurement can accurately reflect the current flow.

For example, a 0.1Ω resistor with a 1A current will produce a 100mV drop, which can be amplified and read by an ADC or comparator.

Key Selection Parameters

1. Resistance Value

• Low resistance minimizes power loss (P = I²R) but requires precise voltage measurement.

• High resistance provides a larger voltage drop but increases heat dissipation.

2. Power Rating (Wattage)

• Must handle the maximum expected current without overheating.

• Example: A 1Ω resistor with 1A current dissipates 1W (I²R).

3. Tolerance & Accuracy

• Precision resistors (1%, 0.5%, or 0.1%) ensure reliable measurements.

• Tight tolerance is crucial for high-accuracy applications like battery management.

4. Temperature Coefficient of Resistance (TCR)

• Defines how resistance changes with temperature (ppm/°C).

• Low TCR (<50 ppm/°C) is essential for stable performance in varying environments.

5. Package Type & Mounting

• Surface-mount (SMD) resistors (e.g., 0603, 1206) are common for compact designs.

• Through-hole resistors may be used for higher power applications.

• Four-terminal (Kelvin) resistors minimize parasitic resistance for high-precision sensing.

Common Applications

1. Battery Management Systems (BMS) – Monitors charge/discharge currents.

2. Motor Control – Measures current in H-bridge drivers for overload protection.

3. Power Supplies – Provides feedback for current regulation.

4. Overcurrent Protection – Triggers shutdown if current exceeds safe limits.

5. LED Drivers – Ensures consistent brightness by regulating current.

PCB Layout Best Practices

• Place the resistor close to the load to minimize trace resistance errors.

• Use a Kelvin (4-wire) connection for high-precision measurements.

• Ensure adequate trace width to handle high currents without excessive heating.

• Avoid thermal stress by placing the resistor away from heat-generating components.

Conclusion

Current sense resistors are simple yet powerful components that enable efficient power monitoring and control. Selecting the right resistor—considering resistance value, power rating, tolerance, and TCR—ensures accurate and reliable performance in your application.

By following best practices in PCB layout and component selection, engineers can optimize their designs for precision current sensing in everything from portable electronics to industrial systems.

External Source:

A Guide to Current Sense Resistors – Ohmite

Have questions about choosing the right current sense resistor? Let us know in the comments!

تُعد مقاومات استشعار التيار (Current Sense Resistors) من المكونات الحيوية في الدوائر الإلكترونية، حيث تتيح قياس التيار بدقة لإدارة الطاقة، مراقبة البطاريات، تحكم المحركات، والحماية من التيار الزائد. تُعرف هذه المقاومات أيضًا باسم مقاومات شنت (Shunt Resistors)، وهي توفر انخفاضًا في الجهد يتناسب مع التيار المار عبرها، مما يسمح للنظم بمراقبة وتنظيم الطاقة بكفاءة.