How to balance the protection and EMC of an electrical power measurement switch (PMS)?

The protection circuits (overvoltage, overcurrent, overheat) of switching devices (such as MOSFETs and IGBTs) in a Power Management System (PMS) may introduce additional EMI problems. For example, rapid turn-off during protection operation can generate high dv/dt, and the protection detection circuit may pick up noise, leading to malfunctions. Careful design is required to balance protection and EMC. Overvoltage protection (e.g., using a TVS diode SMCJ33CA) should be mounted close to the switching transistor, and its grounding lead should be short and thick. For overcurrent detection, the sampling resistor should be a non-inductive resistor (e.g., a metal foil resistor), and its signal line should be a differential pair twisted together.

Before being sent to the comparator, it should be filtered by an RC low-pass filter (e.g., 1kΩ + 1nF) to suppress high-frequency noise. The thermistor (e.g., MF72-10D-7) for overheat protection should have shielded or twisted leads. The turn-off rate after protection triggering should be controllable; a small capacitor (e.g., 100pF) can be added to the turn-off pin of the driver IC to slow down the turn-off speed. Simultaneously, the power supply and ground of all protection circuits must be isolated from noisy power circuits. With this design, the switch protection function is reliable and effective, and it does not generate additional conducted or radiated interference. The system passes relevant EMC tests.