Common Mode Choke


Gowanda designs and manufactures common mode chokes for noise cancellation and filtering applications. Designs include standard types of “core with bobbin” structures (E, EP, EFD, PQ, POT, U and others), toroids and some custom designs. Common Mode Chokes are used where many electrical devices are connected to the same power lines (or power supply lines) and therefore substantial electrical noise can exist on these lines.

What is a Common Mode Choke?

A common mode choke is an electrical filter that is utilized to block  or limit unwanted high frequency alternating current (AC) noise within an electrical system while allowing the desired lower frequency direct current (DC) to pass through. Common mode (CM) noise current is typically radiated from sources such as unwanted radio signals, unshielded electronics, inverters and motors. Left unfiltered, this noise presents interference problems in electronics and electrical circuits.

Selection Considerations for Common Mode Chokes

When selecting a common mode choke for a given application, it is important to consider the specific requirements and restrictions of the system for which it is being installed. Gowanda’s common mode chokes are manufactured in a wide range of sizes and designs to suit a variety of use cases. As a general rule, larger chokes are capable of filtering lower frequencies than smaller chokes, making them suitable for equipment that requires more accurate noise filtering, such as AC/DC outlets.

Key factors to consider when selecting a choke are:

  • Current Rating: to ensure the part does not overheat within the application
  • Impedance vs. Frequency: to ensure it is optimized to attenuate the desired frequencies.
  • Isolation Voltage: to ensure it meets board level requirements between the line and neutral phases.
  • Safety Isolation: to ensure it meets the safety requirements of the end application.
Common Mode Choke Design
  • It is typical for the inductance value of a common mode choke to be specified as a minimum requirement, thus insuring the crossover frequency is not shifted too high.
  • The frequency range of the interfering signal should be provided in order to allow proper calculation of the attenuation of unwanted signal noise in the design.
  • Proper wire sizing is accomplished by specifying the voltage and current levels across, and passing through, the common mode choke.

Common mode choke filter, line inductor, and differential choke designs vary widely in terms of power rating, inductance, voltage level (low to high), operating frequency, size, impedance, bandwidth (frequency response), packaging, winding capacitance, and other parameters.


Common mode chokes are commonly used to reduce or eliminate electromagnetic interference (EMI) in industrial applications that require a steady and reliable current without interruption. Typical electrical and electronic devices that may use common mode chokes include:

  • Audio/Visual (AV) signaling equipment
  • Conveyors and elevators
  • Electrical Ballasts
  • HVAC systems
  • Industrial Tool Drives
  • LED Lights
  • Medical Equipment
  • Oil & Gas Control Systems
  • Robotic Equipment
  • Switching Regulators
  • Switch Mode Power Supplies
  • Train Signaling Systems
  • Variable Frequency Drives (VFDs)

Radial Lead Transformer

Series L µH DCR Ohms Current Rating mA DC
CMF4H 100 – 10000 0.0025 – 0.390 1.20 – 15
CMF4HC 100 – 10000 0.004 – 0.390 1.20 – 12
CMF4VM 100 – 10000 0.0025 – 0.390 1.20 – 15
CMF5H 750 – 15000 0.009 – 0.250 2.0 – 12.50
CMF5VM 750 – 15000 0.009 – 0.250 2.20 – 11.80

Surface Mount Transformer

Series L µH DCR Ohms Current Rating mA DC
CMF1SM 100 – 1000 0.026 – 0.658 0.50 – 2.80
CMF2SM 100 – 1000 0.035 – 0.210 1.20 – 3.00
CMF3SM 25 – 2500 0.010 – 0.150 2.20 – 8.50
CMF61SM 25 – 2200 0.010 – 0.750 0.18 – 3.0
CMF63SM 33 – 4700 0.007 – 1.050 0.25 – 5.50
CMF64SM 100 – 10000 0.006 – 0.90 0.33 – 7.0
CMF65SM  100 – 15000 0.005 – 1.10 0.35 – 8.50
CMN3VSM 180 – 10000 0.0019 – 0.0347 3.80 – 16.40

Custom Products

Gowanda welcomes the opportunity to assist its customers with application-specific designs for a particular application where the requirements can not be met by off-the-shelf components.

Our capabilities in design, development, production and testing are extensive. If you are interested in custom products please contact us for assistance.