The Role of Common Mode Chokes in EMI Suppression

The Role of Common Mode Chokes in EMI Suppression


Electromagnetic interference (EMI) is a common problem in electronic circuits, causing disruptions and malfunctions in devices. It is essential to mitigate EMI to ensure the proper functioning of electronic equipment. One effective solution for EMI suppression is the use of common mode chokes. Let us understand more!

Understanding EMI

To better understand the importance of common mode chokes in EMI suppression, let's dive deeper into the concept of electromagnetic interference. EMI can be broadly classified into two categories: conducted EMI and radiated EMI.

Conducted EMI refers to the unwanted noise signals that propagate through electrical conductors, such as power lines or data cables. These noise signals can be generated by various sources, including switching power supplies, digital circuitry, or high-frequency components. Conducted EMI can disrupt the normal operation of nearby electronic circuits and devices, leading to signal distortions or data corruption.

Radiated EMI, on the other hand, occurs when electromagnetic waves are emitted from a source and propagate through space. These waves can be picked up by nearby electronic circuits, causing interference and potential malfunctions. Radiated EMI sources include radio frequency (RF) transmitters, wireless devices, or electromagnetic radiation from power lines.

Both conducted and radiated EMI can have detrimental effects on electronic systems, resulting in reduced performance, increased error rates, or even complete system failure. Therefore, it is crucial to employ effective EMI suppression techniques, such as the use of common mode chokes.

About Common Mode Chokes

Common mode chokes are specifically designed to address conducted EMI by suppressing common mode noise signals. Common mode noise refers to noise signals that appear in phase on both conductors of a transmission line. These noise signals are often caused by imbalances in the circuit or external electromagnetic disturbances.

The construction of common mode chokes involves winding the inductor coil on a magnetic core. The windings are configured in such a way that they create two identical coils in parallel. When the noise signals flow through the choke, they induce equal and opposite voltages in parallel windings. As a result, the common mode noise signals effectively cancel each other out, while allowing the differential mode signals (the desired signals) to pass through unaffected.

In addition to common mode noise suppression, common mode chokes also provide differential mode filtering to a certain extent. Differential mode noise refers to noise signals that appear out-of-phase on the conductors of a transmission line. Although common mode chokes are not specifically designed for differential mode noise, they can still provide some level of attenuation due to their inherent inductive properties.

Function of Common Mode Chokes

Common mode chokes serve several important functions in electronic circuits, making them an essential component in EMI suppression strategies.

  1. Noise Suppression: The primary function of common mode chokes is to suppress unwanted noise signals, specifically common mode noise. By using the principle of electromagnetic induction, the chokes generate opposing voltages that cancel out the common mode noise signals, preventing them from interfering with the desired signals.

  1. Impedance Matching: Common mode chokes also provide impedance matching between the source and load. They present a high impedance to the common mode noise signals, effectively blocking their passage. At the same time, they offer low impedance to the differential mode signals, allowing them to pass through with minimal attenuation.

  1. Filtering High-Frequency Noise: Common mode chokes are particularly effective in filtering high-frequency noise signals, which are a common source of EMI. The inductive characteristics of the chokes enable them to attenuate high-frequency noise more effectively than other passive components, such as capacitors or resistors.

  1. DC Biasing: In some applications, common mode chokes can also function as a DC bias choke. They help isolate the DC biasing of circuits by blocking the DC current flow while allowing the AC signals to pass through. This feature is useful in applications where DC biasing needs to be separated from AC signals.

Advantages of Common Mode Chokes

  1. EMI Suppression: Common mode chokes excel at reducing unwanted noise signals, thereby enhancing the electromagnetic compatibility (EMC) of electronic circuits. This leads to improved device performance and reliability.

  1. Compact and Cost-Effective: Common mode chokes are available in various sizes and configurations, making them adaptable to different applications. They offer a cost-effective solution for EMI mitigation without requiring complex circuitry or active components.

  1. Easy Integration: Common mode chokes can be easily integrated into existing circuits or added during the design phase. Their compact form factor enables efficient space utilization, making them suitable for both small-scale and large-scale electronic systems.

Application of Common Mode Chokes

Common mode chokes find wide-ranging applications across various industries and electronic systems. Here are some key areas where their use is prevalent:

  1. Power Supplies: Common mode chokes are commonly employed in power supply circuits to suppress EMI generated by switching power converters, rectifiers, or transformers. They help ensure stable and clean power delivery, reducing the risk of interference and improving overall system performance.

  1. Data and Communication Lines: In data transmission lines, such as Ethernet cables, USB connections, or HDMI interfaces, common mode chokes play a vital role in minimizing electromagnetic interference between devices. They help maintain signal integrity and data accuracy, particularly in high-speed communication applications.

  1. Industrial and Automotive Electronics: The industrial and automotive sectors often deal with high levels of electrical noise and EMI sources. Common mode chokes are extensively used in these applications to suppress noise generated by motors, actuators, sensors, and other components. They help prevent disruptions in control systems, ensuring reliable operation in harsh environments.

  1. Audio and Video Equipment: Common mode chokes are crucial in audio and video equipment, such as amplifiers, mixers, and display devices. They help eliminate unwanted noise and interference, ensuring high-quality signal transmission and minimizing distortions in audio and video output.

  1. Medical Devices: Common mode chokes are also widely utilized in medical devices where electromagnetic compatibility is critical. They help minimize the risk of interference between medical equipment, ensuring accurate measurements, reliable operation, and patient safety.

  1. Renewable Energy Systems: In renewable energy systems, such as solar inverters and wind turbines, common mode chokes are used to mitigate EMI generated during power conversion and distribution. They assist in maintaining power quality, reducing harmonics, and ensuring compliance with grid interconnection standards.


Common mode chokes are indispensable components for EMI suppression in electronic circuits. Their ability to attenuate unwanted noise signals makes them a valuable tool for ensuring electromagnetic compatibility. Engineers can achieve improved system performance and reliability by incorporating common mode chokes into various applications, such as power supplies, data lines, industrial electronics, and audio/video equipment. Shah Electronics has acquired exceptional expertise in this field and is poised to provide valuable assistance. As a leading company with a specialization in manufacturing and supplying electronic solutions, including transformers, conductors, and other related products, we would be happy to help you!



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