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Our range of Common Mode Chokes includes both radial leaded and SMD types.

A common mode choke is an electrical filter that blocks high frequency noise common to two or more data or power lines while allowing the desired DC or low-frequency signal to pass. 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.

How do common mode chokes work?

In normal or differential (single choke) mode, current travels on one line in one direction from the source to the load, and in the opposite direction on the return line that completes the circuit. In common mode, the noise current travels on both lines in the same direction.

This means that the combined magnetic flux adds to create an opposing field to block the noise. In differential mode, the current travels in opposite directions and the flux subtracts or cancels out so that the field does not oppose the normal mode signal.

How to choose a Common Mode Choke?

The main criteria for selecting a common mode choke are:
  1. Required impedance: How much attenuation of noise is needed?
  2. Required frequency range: Over what frequency bandwidth is the noise?
  3. Required current handling: How much differential mode current must it handle?

Types of common mode chokes

  1. High-Speed and Super-Speed Data Line EMI Chokes
  2. Data Line Common Mode EMI Chokes
  3. Data/Power Line Common Mode EMI Chokes
  4. Surface Mount Power Line Common Mode EMI Chokes
  5. Through-Hole Power Line Common Mode EMI Chokes

Applications for common mode chokes

Common mode choke coils are suited for noise suppression on lines with large current flows, such as AC/DC power supply lines. The distortion of the waveform is reduced. Common mode choke coils are suited for noise suppression on lines where signal waveform distortion causes a problem, such as video signal lines.

Common mode choke application example

As the auto industry’s boom continues, the adoption of electronic devices in automobiles has grown rapidly. Thanks to this trend, vehicles can now be equipped with a variety of features, such as infotainment systems, ADAS (advanced driver-assistance systems), navigation systems, OBD (on-board diagnostics), and others.

CAN bus (Controlled Area Network) is one of the communication standards that allows all these features to function in unison. It uses two-wire differential signalling to send and receive data from the different devices in the network. While the nodes of the bus can be near other EMI sources in the vehicle, the design of a robust CAN bus that can withstand all incoming noise is integral to delivering a reliable and safe vehicle. In addition to other filtering techniques, common mode chokes are one of the devices that are used to combat noise in a CAN bus.