How to match the parameters of the common-mode inductor in an electrical power measurement switch (PMS)?

Selecting a common-mode inductor for a PMS requires comprehensive matching parameters based on the interference frequency, impedance requirements, operating current, and installation space.

First, determine the target suppression frequency band: for 20-100kHz interference from switching power supplies, choose an inductor with a larger inductance value, such as CMZ1211-501T (500μH); for high-frequency noise above MHz, pay attention to the impedance curve at the target frequency and select CMZ2012A-900T (90μH, Z>800Ω at 100MHz).

Second, the rated current must be greater than the maximum operating current flowing through the inductor (including surge current), typically with a 50% margin. For example, for a main power line current of 10A, choose a model with a rated current of 15A or higher. DC superposition characteristics also need to be considered to avoid excessive inductance attenuation under high current. Structurally, prioritize models with symmetrical windings and small inter-turn capacitance to reduce differential-mode to common-mode conversion.

During installation, ensure the inductor maintains a distance of at least 5mm from adjacent components (especially Y capacitors) to prevent magnetic field coupling. A well-matched common-mode inductor, combined with a Y capacitor, can provide more than 40dB of common-mode attenuation in the 1-30MHz frequency band, enabling the PMS to successfully pass the EN 55032 conducted emission test.