Differential Mode vs. Common Mode Chokes: Their Purpose, Structure, Applications, and How They Work

Electronic devices rely heavily on electromagnetic interference (EMI) shielding devices for proper functioning. Two common types of EMI are common mode noise and differential mode noise. Designers and engineers must be able to identify the differences between common mode vs. differential mode noise when developing components to mitigate them.

Read on to learn about the distinct characteristics of common mode and differential mode noise and the types of chokes required for each one.

Common Mode Noise vs. Differential Mode Noise

Common mode noise occurs when both lines have the same signal, traveling in the same phase and direction. When the same signal is applied to both inputs in operational amplifiers, it results in common mode voltage gain.

Differential mode noise, also called normal mode noise, happens when the signals on two lines flow in opposite directions.

Key Differences Between Differential Mode and Common Mode Chokes

Understanding the key differences between these types of chokes will help you select the right shielding product for your specific application.

Purpose & Functionality

• Differential Mode Chokes: Eliminate differential mode noise that occurs when the noise gets added to a single line and mixes with the carried signal. These chokes allow lower-frequency AC or DC to pass, effectively blocking high-frequency AC noise.
• Common Mode Chokes: Capable of suppressing common mode noise, where signals travel on both lines of a conductor in the same direction. Common mode chokes can block high-frequency noise on both lines to allow the desired signal to pass.

Structure

• Differential Mode Chokes: An inductor of wire wound into a coil around a core.
• Common Mode Chokes: At least two coils of insulated wire wound around a magnetic core, with each coil winding in series with a particular conductor.

Signal Direction

• Differential Mode Chokes: Noise occurs on a single line in series with the power supply line, with the noise flowing in the same direction as the power supply line.
• Common Mode Chokes: Both lines have noise currents flowing in the same phase and direction. The currents in the wires generate magnetic fields that combine to deliver high impedance to the noise signals.

Operation

• Differential Mode Chokes: Create high impedance to high-frequency noise by blocking or attenuating it. The desired low-frequency AC or DC can pass through the line with minimal resistance.
• Common Mode Chokes: Create high impedance to common mode noise, blocking or attenuating the currents. The desired differential mode currents, which flow in opposing directions and create opposing magnetic fields, cancel one another out to allow the desired signal to pass through with little resistance.

Applications

• Differential Mode Chokes: Frequently used to reduce high-frequency AC noise in power supplies. Often found in industrial equipment, telecommunications, and consumer electronics to minimize noise and maintain reliability and performance.
• Common Mode Chokes: Crucial for meeting regulatory standards set by the Federal Communications Commission (FCC) to ensure noise does not cause interference with electronic equipment. Common mode chokes are used in signal lines, power supply cables, electronic ballasts, LED lighting, transportation systems, and medical equipment.

Noise Suppression

• Differential Mode Chokes: Best suited for circuits carrying low-frequency AC or DC. The inductor size depends on the current it needs to handle and the inductance requirements.
• Common Mode Chokes: Can suppress common mode noise, particularly in telecommunication and industrial systems. They maintain low electrical resistance while providing high impedance to noise signals, resulting in minimal power loss.

How CoolBLUE^® Cores Protect Against Differential Mode and Common Mode Noise

CoolBLUE^® cores from MH&W are nanocrystalline toroids that significantly reduce the currents that can damage motor bearings in modern high-power inverter systems with high switching frequencies. Without protection from differential mode and common mode noise, motor bearings quickly corrugate, leading to lubrication breakdown and failure of the entire motor. 

Key benefits of CoolBLUE^® cores are:

• Minimize over-current peaks at motor terminals
• Suppress asymmetrical electromagnetic interference currents generated from the parasitic capacities of the motor and the motor cable
• Increase the service life of motor bearings
• Reduce standstill periods and maintenance costs

Differential and Common Mode Chokes from MH&W

Effectively managing electromagnetic interference (EMI) is vital for the reliability and proper functioning of electronic devices. MH&W’s CoolBLUE^® cores offer an innovative solution for differential mode and common mode noise concerns, significantly reducing over-current peaks and suppressing asymmetrical EMI currents.

MH&W is an industry-leading North American supplier of nanocrystalline components. Our capabilities, experience, foresight, and product knowledge have resulted in effective filter solutions for electric vehicle (EV), variable frequency drive (VFD), solar, wind, and many other applications.

Contact us today to learn more about our innovative noise-filtering products. Request a quote to get started on your unique solution.