Common mode inductors can play an anti-EMC role in daily use, and are very widely used in controllers in industrial production scenarios. They can be used in power supplies, and can also be used in anti-EMC aspects of communication circuits. The relevant information is sorted out below, hoping to be helpful for everyone's design.
1. Common mode inductance
(Common mode Choke), also called common mode choke coil, common mode inductor is a common mode interference suppression device with ferrite as the core. It consists of two coils with the same size and the same number of turns symmetrically wound around the On the same ferrite ring core, a four-terminal device is formed, which can suppress the large inductance of the common mode signal, but has little effect on the small leakage inductance of the differential mode signal. The principle is that the magnetic flux in the magnetic ring is superimposed on each other when the common mode current flows, so that it has a considerable inductance, which inhibits the common mode current, and when the two coils flow through the differential mode current, the magnetic flux in the magnetic ring Through canceling each other, there is almost no inductance, so the differential mode current can pass without attenuation. Therefore, common-mode inductors can effectively suppress common-mode interference signals in a balanced line, but have no effect on differential-mode signals normally transmitted by the line.
2. Performance characteristics
It has a very high initial magnetic permeability, has a large impedance and insertion loss under the geomagnetic field, has an excellent suppression effect on interference, and exhibits no resonance insertion loss characteristics in a wide frequency range. l High initial magnetic permeability: 5-20 times that of ferrite, so it has greater insertion loss, and the suppression effect on conduction interference is much greater than that of ferrite. l High saturation magnetic induction
: 2-3 times higher than ferrite. It is not easy to be magnetized to saturation in the occasion of strong current interference. l Excellent temperature stability: higher Curie temperature, in the case of large temperature fluctuations, the performance change rate of the alloy is significantly lower than that of ferrite, with excellent stability, and the performance change is close to linear. l Flexible frequency characteristics: It is more flexible to adjust the process to obtain the required frequency characteristics. Through different manufacturing processes and appropriate coil frying, different impedance characteristics can be obtained to meet the filtering requirements of different bands, making its impedance value much higher than that of ferrite.
3. Working principle of common mode inductor
According to the right-hand spiral theorem, when the differential-mode current flows through the common-mode inductance coil, two mutually canceling magnetic fields are generated; when the common-mode current flows through the common-mode coil, two mutually reinforcing magnetic fields are generated, making the entire coil impedance higher. Attenuates common-mode currents.
Common mode inductance can be measured, the measurement method is as follows:
4. Production of co-model files
4.1. Bifilar - high symmetry, relatively small differential mode impedance
4. Two sets of coils are wound separately (Sectional) - low symmetry, relatively large differential mode impedance
Applications:
Power grid common mode interference filtering
Anti-shock and interference design of electronic equipment and electronic instrument power supply
In addition to being used in power systems, common mode inductors can also be used in communication circuits, such as the following figure: the use in CAN bus and RS485 bus:
Schematic diagram of CAN bus
Schematic diagram of the use of RS485 bus