LN122

LN Series Common Mode Chokes

LN122 Series common mode toroidal chokes provide an efficient means of filtering of filtering supply lines with in-phase signals of equal amplitude, enabling equipment to meet stringent electrical emission requirements.
Wide frequency ranges can be filtered by using high and low inductance common mode chokes in series. Differential mode signals can be significantly attenuated when used in conjunction with input and output capacitors.

Related Encyclopedia

Inductors are passive, two-terminal electrical components that store energy in a magnetic field when electric current flows through them. They generally consist of an insulated wire wound into a coil around a core. Common mode chokes act as passive electronic inductors that filter out frequencies. High frequencies are specifically eliminated, while low frequencies are allowed to pass through an electronic system. With such properties, they have proven to be very useful when used in electrical transformers.

Construction
Common mode chokes consist of a magnetic or ferromagnetic core and two wire windings in the form of toroidal inductors. The two windings are identical except that they are wound in opposite directions. The choke can be large or small, with no fixed number of windings, but the primary coil delivers current from the AC mains and the secondary winding. This creates a balance by cancelling the flux from the primary coil. When common mode current is used for different circuits, the choke blocks out the noise in the AC mains.
Finding the right choke
It is very important to find the right common mode choke, and to do this you need to be aware of the level of common mode noise suppression required. one technique for achieving maximum efficiency is to select the lowest frequency for common mode noise suppression. To resist the noise without affecting the signal, high impedance is applied at unwanted frequencies. Unwanted noise is cancelled when there is equal signal cancellation in the common mode choke.

The best chokes for filtering out unwanted electromagnetic interference currents without causing signal degradation work well with filtering out unwanted frequencies in power lines. Common mode chokes can also be used to generate radio frequency interference in networks that don’t use unshielded twisted pair cable. The overall effect is a zero impedance created by short signals to ground potential.

Why the name?
You may wonder why chokes are called “common mode” chokes. The reason is that chokes are present on both the neutral and the line. Now that you have understood what a common mode choke is, how it is constructed and how it works, let us help you find the right choke for your application.