How do isolation, filtering, and protection functions of a smart controller (PAC) work together?

In a Power Arrangement Controller (PAC), isolation, filtering, and protection must work together to improve EMC. Isolation is used to break ground loops, such as by using isolated power supplies and digital isolators. Filtering is used to attenuate noise, such as by using common-mode inductors and capacitors. Protection is used to suppress transients, such as by using TVS and varistors.

In a collaborative design, protection is implemented first, followed by filtering, and then isolation: protective devices are placed at the interface to absorb transients, then high-frequency noise is filtered out by filters, and finally the signal enters the internal circuit through an isolator.

For grounding, the grounding of the protection and filter is connected to the chassis, while the grounding on both sides of the isolator is separate. Tests show that a collaborative design can enable the PAC to pass multiple standard tests such as IEC61000-4-2/4/5/6/8, and improve system stability by an order of magnitude.