Learn the inductance amount of common-mode inductance. Follow the inductance manufacturer (professionally supplied: axial inductor, radial inductor) to learn:
Differential mode current: A pair of signals of the same size and opposite direction on a pair of differential signal lines, usually used in a circuit
The current, for a signal line, is the current flowing between the signal line and the signal ground.
Common mode current: A pair of signals (or noises) of the same size and direction on a pair of differential signal lines.In the circuit,
Generally, ground noise is transmitted by common mode current, so it is also called common mode noise.
There are many ways to suppress common-mode noise. In addition to reducing common-mode noise at source, common mode inductance is usually used to filter common-mode noise, that is, to block common-mode noise out of the target circuit.That is, a common mode choke in series in a circuit.The objective is to increase the impedance of the common-mode circuit so that the common-mode current is consumed and blocked (reflected) by the choke, thereby suppressing common-mode noise in the circuit.
The principle of a common-mode choke or inductor
If a pair of coils are wound in the same direction on a magnetic ring of some magnetic material, magnetic flux is generated in the coil due to electromagnetic induction when an alternating current passes through the coil.For differential mode signals, the magnetic flux generated by the magnetic ring is the same in size and opposite in direction, and the two cancel each other out, so the differential mode impedance generated by the magnetic ring is very small.For common-mode signals, the magnetic flux generated is of the same magnitude and direction, and the two are superimposed on each other to generate a large common-mode impedance of the magnetic ring.This characteristic makes the common mode inductance have less influence on the differential mode signal and has better filtering performance to the common mode noise.
(1) When the differential mode current passes through the common-mode coil, the magnetic field line is in opposite direction and the induced magnetic field is weakened. It can be seen from the direction of the magnetic field line in the figure below that the solid line arrow represents the direction of the current and the dashed line represents the direction of the magnetic field
(2) The common-mode current passes through the common-mode coil, and the magnetic field is strengthened due to the same direction of the magnetic field line. It can be seen from the direction of the magnetic field line in the figure below that the solid line arrow represents the direction of the current and the dashed line represents the direction of the magnetic field
Common-mode inductance of coil or called self-induction coefficient, we know that the inductance is produces the ability of the magnetic field, the common mode or common-mode inductor coil, when the common-mode current flows through a coil, due to the magnetic field lines in the same direction, without taking into consideration under the condition of the leakage inductance, magnetic flux, its principle is mutual inductance, below coil coil magnetic field lines through the blue, red and blue coil magnetic field lines also through the red coil, induction each other.
From the point of view of inductance, inductance is multiplied, magnetic chain represents the total magnetic flux, the common-mode inductor, when magnetic flux is doubled, circle number has not changed, the current didn't also did not change, so mean increased inductance for 2 times, means that the equivalent permeability into 2 times.
How can equivalent permeability be doubled? From the following inductance formula, since the number of turns N does not change, the magnetic circuit and the cross-sectional area of the magnetic core are determined by the physical size of the magnetic core, so there is no change. The only reason is that the permeability U is doubled, so more magnetic flux can be generated
Common-mode inductor in common mode, therefore, when an electric current passes through, work under the mutual inductance model, under the effect of mutual inductance, the equivalent inductance is cost increase, therefore common mode impedance will be multiplied, and the common mode signal has good filtering effect, also is the common mode signal with large impedance block, don't let it pass the common-mode inductor, also is not to let this signal transmission to the next level of the circuit, the following is the inductive reactance ZL.
Know common-mode inductor under the mode of common mode inductance, is the main clue to know mutual inductance, magnetic components of all, no matter what name as long as mastering the form of the change of the magnetic field, magnetic field changes through the phenomenon to essence, also easy to understand, moreover we always grasp the magnetic field lines, it is our understanding the visual form of the magnetic field, consider whether the same side or different name or concept of the mutual inductance phenomenon or magnetic field, we are drawing the lines of magnetic force to realize their - master "magnet winding method" is explained before.
Post time: Dec-16-2020