How to isolate noise from the switching power supply of an HMI (Human Machine Interface)?

Isolating noise from HMI switching power supplies primarily involves three levels: spatial isolation, conducted isolation, and grounding isolation. Spatial isolation refers to placing the power supply modules, especially noise sources such as transformers, power inductors, and switching transistors, in areas far from sensitive analog and high-speed digital circuits on the PCB layout, potentially using ground lines or shielding for physical separation. Conducted isolation involves using isolation devices along the power supply path, such as using isolated DC-DC modules at the secondary output of the switching power supply, or using common-mode inductors like the CMZ3225A-101T, to confine noise locally.

For noise conducted through the ground plane, a segmented ground plane combined with single-point connections using ferrite beads can isolate the power supply ground from other circuit grounds. Using shielding layers on the input and output cables of the switching power supply, and grounding the shielding layer at a single point on the power supply side, effectively prevents noise radiation through the cables. Optimizing the EMC design of the switching power supply itself is also fundamental, such as reducing the dv/dt of the switching transistors, using soft-switching technology, and adding shielding layers to the primary and secondary sides of the transformer. By comprehensively utilizing layout, filtering, and grounding technologies, and selecting high-performance isolation and filtering devices from Audiotech, the noise of the switching power supply can be effectively limited to a minimum, preventing it from interfering with the normal operation of other functional modules of the HMI.