CAB-4.0-3.3

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A common mode choke (CAB 4.0 - 3.3) is a type of EMI filter that attenuates electromagnetic interference (EMI) transmitted along a conductor, usually over cables or wires. It has well-established applications in cable and wiring systems, and is frequently used in signal and power line applications. Common mode chokes can also be used in power line filter assemblies to reduce or eliminate conducted interference from a power system.

Common mode chokes are basically two inductors connected in parallel, each with a separate winding around a common core, usually ferrite. The inductive reactance created by these inductors effectively isolates the returned ground currents from the wideband high frequency interference signals that are common with data and communication systems. The two inductors together act as a signal filter, blocking out high frequencies while letting low frequencies pass. This is known as common mode reduction.

Common mode chokes are also capable of attenuating Synchronous Common Mode Currents (SCMCs), which are parasitic high-frequency switching currents that flow over the power lines and return to the power supply through the neutral line. These currents can cause interference to other connected devices and generate excess heat, and if left unattended can damage sensitive components.

The inductor’s radius plays an important role in common mode choking. As the radius increases, the choking effect increases, thereby lowering the loop inductance and reducing the high frequency interference. Additionally, if the inductor radius is too small, it may not be able to generate the required high chokes effect to attenuate the high frequency currents.

Common mode chokes can also be used for power quality monitoring. By monitoring the common mode currents in a power system, operators can detect short circuits and ground faults, as well as spikes and sags in the line voltage.

Common mode chokes are also used for power line immunization. By connecting a common mode choke between two points on a power line, the interference causing common mode currents are attenuated or blocked. This creates a higher immunity for the connected devices from electrical noise, thereby improving their performance.

Finally, common mode chokes are also used for filtering in mixed-signal circuits and combinational logic systems. In mixed-signal circuits, there are both analog and digital signals present, and the chokes can filter out the electrical noise created by the switching of the digital signal, thereby reducing interference. In combinational logic systems, the common mode chokes can be used to reduce the loop inductance and lower the impedance of the lines, allowing faster logic switching speeds.

In conclusion, common mode chokes are important components used to reduce Electro-Magnetic Interference on cables and in circuit boards. The reactancing effect of two inductors connected in parallel effectively blocks out high frequencies while allowing low frequencies to pass. Common mode chokes can be used for power quality monitoring, power line immunization and filtering in mixed-signal circuits.

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