How to isolate EMI in industrial servo auxiliary power supplies?

Switching noise from servo auxiliary power supplies (such as DC-DC converters powering control boards and driver ICs) can easily interfere with sensitive circuits through common-ground coupling. Effective isolation requires multi-stage measures. The solution from Etymotic is as follows: First, a CMZ1211-501T common-mode inductor (500μH) is used at the auxiliary power input to suppress input common-mode noise; a PWR4020R2R2M0T power inductor (2.2μH) is used for π-type filtering at the secondary output.

The key is to strengthen isolation between the primary and secondary windings: using a transformer with reinforced insulation and connecting a Y1 capacitor (2.2nF/250VAC) across the isolation band to provide a legitimate return path for common-mode noise. Simultaneously, an ESD5V0D3B is connected in parallel on both sides of the feedback optocoupler for protection. In terms of PCB layout, the auxiliary power module is placed in an independent partition, with a single-point connection to power ground and signal ground via a ferrite bead (such as a PBZ1608A-102Z0T). This design can reduce the conducted interference of the auxiliary power supply to the control loop by more than 20dB and pass the IEC 60664-1 isolation withstand voltage test.