1. Basic concepts and influencing factors of common mode rejection ratio (CMRR)
In practical applications, the degree of suppression of common mode interference by Common Mode Filter Inductor is usually measured by Common Mode Rejection Ratio (CMRR). Common Mode Rejection Ratio is an important indicator of the ability of Common Mode Filter Inductor to suppress common mode signals. It is defined as the ratio of common mode input signal to common mode output signal, usually in decibels (dB). The common mode rejection ratio of Common Mode Filter Inductor is affected by many factors. The first is the inductance. A larger inductance can generally provide better common mode interference suppression effect. This is because the blocking effect of inductance on common mode current increases with the increase of inductance. Secondly, the core material also plays a key role. For example, ferrite core has a higher magnetic permeability, which can enhance the ability of inductance to suppress common mode interference, thereby improving the common mode rejection ratio.
2. Typical suppression degree in different application scenarios
In different practical application scenarios, the degree of suppression of common mode interference by Common Mode Filter Inductor varies. In some common consumer electronic products, such as mobile phone chargers, Common Mode Filter Inductors can usually suppress common mode interference by about 20-40dB. This suppression level is sufficient to meet general electromagnetic compatibility (EMC) requirements and prevent the common mode interference generated by the charger from affecting other devices. In communication equipment with higher requirements for electromagnetic compatibility, such as base station equipment, Common Mode Filter Inductors may need to achieve a common mode rejection ratio of 60-80dB or even higher. This is because base station equipment needs to work in a complex electromagnetic environment and must strictly control common mode interference to ensure the quality and stability of communication signals.
3. Suppression effect under synergy with other components
Common Mode Filter Inductors often work in synergy with other components in actual circuits, and this synergy will affect the final degree of suppression of common mode interference. For example, when forming a filter circuit with a capacitor, the combination of inductors and capacitors can form a specific filter network. Capacitors can provide a low impedance path for high-frequency common mode interference, while inductors prevent the passage of common mode current. Under this synergy, the ability of the entire filter circuit to suppress common mode interference may be significantly enhanced. In some well-designed power filter circuits, by reasonably matching Common Mode Filter Inductors and capacitors, common mode interference can be suppressed to more than 80-100dB, thus meeting the requirements of high-precision electronic equipment for power purity.
4. Limitations and improvement directions in practical applications
However, in practical applications, the degree of suppression of common mode interference by Common Mode Filter Inductors is also limited. For example, with the increase of frequency, factors such as parasitic capacitance and core loss of the inductor will affect its filtering effect, resulting in a decrease in the common mode rejection ratio. In addition, in high current and high power application scenarios, Common Mode Filter Inductors may saturate, thereby reducing the ability to suppress common mode interference. In order to overcome these limitations, the current improvement directions include the use of new core materials to reduce core loss, optimizing the structural design of the inductor to reduce parasitic capacitance, and developing Common Mode Filter Inductors with higher saturation currents. These improvement measures help to improve the suppression of common mode interference by Common Mode Filter Inductors in a wider range of application scenarios.
