A common mode choke works as a passive electronic inductor that filters out frequencies. It’s often used to specifically eliminate high frequencies while low frequencies are allowed in an electronic system.
This simple efficient component is designed with one magnetic or ferromagnetic core and a two wire winding in the shape of a toroidal inductor. These two windings are identical other than they are wound in opposite directions. The choke can be big or small and does not have a set number of windings.
The primary coil delivers current from the AC mains and the secondary winding. This structure creates a balance by canceling out the flux from the primary coil. When using common aka differential mode current for various circuits, the choke helps block out noise in the AC mains. The word common is used due to the presence of chokes on both the neutral and the mains.
Finding the Right Choke
In order to find the appropriate common mode choke, you must be aware of the suppression level needed for the common mode noise. One technique for achieving maximum efficiency is to choose the lowest frequency for common mode noise suppression. High impedance is applied at unwanted frequencies to resist the noise without affecting the signal. Unwanted noise is canceled when there is equal signal cancellation in the common choke mode.
The best chokes useful for filtering out unwanted electromagnetic interference (EMI) currents without causing signal degradation work well with filtering out undesirable frequencies in power lines. Common mode chokes also can be used to generate Radio Frequency Interference (RFI) in networks that don’t use an Unshielded Twisted Pair (UTP) cable. The overall effect of common mode chokes is zero impedance, as a result of short signals to ground potential.
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Categories: Electronic Components